=== seq 5 ===

Pamphlet T 462 CORNELL UNIVERSITY LIBRARY KOS CORNELL UNIVERSIT UNDED BY EZRA CORNELL Cornell University Library Pamphlet T 462 Modifications of the plan of the new Cro 3 1924 032 873 592 olin , str1 Modifications of the Plan of the New Croton Dam By WILLIAM R. HILL Read before the American Water Works Association at St. Louis , Mo. , June 8th , 1904 Pamphlet 462 21 13861282 ES MODIFICATIONS OF THE PLAN OF THE NEW CROTON DAM . BY WILLIAM R. HILL . The responsibility of the engineer in charge of con- structing dams and reservoirs , is but vaguely appreciated by the public . In view of the many disastrous failures that have occurred , due to faulty plans and poor con- struction , it is made imperative for the engineer to exercise his best powers to insure proper and substantial struc- tures . There is , perhaps , no other field of engineering that develops in the course of construction so many new conditions and unexpected obstacles , and when the en- gineer finds it necessary to make radical changes in the plans , even though involving heavy expenditures and sub- jecting himself to severe criticism , it is his bounden duty to make these changes . The writer had the honor of being Chief Engineer of the Aqueduct Commission of the City of New York , from January Ist , 1900 , to October 14th , 1903. During his incumbency the new Croton Dam was under construc- tion . The purpose of this paper is to explain , as briefly as possible , the original plan of this structure and the im- perative necessity of its modification , and to answer a general demand made upon the writer that would seem to indicate a very widespread interest in these rotable changes .

The writer had the honor of being Chief Engineer of the Aqueduct Commission of the City of New York , from January Ist , 1900 , to October 14th , 1903. During his incumbency the new Croton Dam was under construc- tion . The purpose of this paper is to explain , as briefly as possible , the original plan of this structure and the im- perative necessity of its modification , and to answer a general demand made upon the writer that would seem to indicate a very widespread interest in these rotable changes . Had the work continued under the original plan it might have resulted not only in the failure of the structure itself but have been the cause of immeasurable loss to this great city of its supply of water in addition to an appalling destruction of life and property . The boroughs of Manhattan and Bronx , of an estimated population of 2,200,000 are dependent almost entirely upon the Croton River for their supply of water ; in fact , they have no other supply , except the comparatively small quantity ( 20,000,000 gallons per day ) from the Bronx and Byram Rivers , small as compared with 290,000,000 gallons , the present daily consumption of these two boroughs . The natural flow of Croton River in dry seasons was judged insufficient to supply the city as early as 1843 , now more than 60 years ago , so Croton Lake of a capac- ity of two billion gallons , was then created by building the old Croton Dam . Since then , from time to time , six other reservoirs , having an aggregate capacity of 40,000,000 , - 000 gallons , have been built on the principal tributaries of the river , above the lake , for the purpose of collecting water in wet seasons , to be discharged into the lake as re- quired for use .

The natural flow of Croton River in dry seasons was judged insufficient to supply the city as early as 1843 , now more than 60 years ago , so Croton Lake of a capac- ity of two billion gallons , was then created by building the old Croton Dam . Since then , from time to time , six other reservoirs , having an aggregate capacity of 40,000,000 , - 000 gallons , have been built on the principal tributaries of the river , above the lake , for the purpose of collecting water in wet seasons , to be discharged into the lake as re- quired for use . The city has no auxiliary supply , and no lakes or rivers that could be used as such in case of an emergency , hence an accident to a reservoir might result in so great a loss of water as to cause a water famine , truly styled one of the world's greatest disasters . The new Croton dam is located about thirty - seven miles from the Central Park reservoirs , it is on the Cro- ton River , about two and one - half miles below the old Croton dam . Its purpose is to enlarge Croton Lake , in- creasing its capacity from two to thirty - two billion gallons and its length from five and one - half to nineteen and three- quarter miles . The old dam will be sumberged , as the flow line will be raised thirty - six feet . The clearing of this great basin for the reservoir , twen- ty miles in length , was in itself an extraordinary under- taking , embracing the clearing of all timber , the removal of three villages , numberless buildings , farm houses and cemeteries and the abandonment and reconstruction of railroad tracks , telegraph and telephone lines , highways and bridges .

The old dam will be sumberged , as the flow line will be raised thirty - six feet . The clearing of this great basin for the reservoir , twen- ty miles in length , was in itself an extraordinary under- taking , embracing the clearing of all timber , the removal of three villages , numberless buildings , farm houses and cemeteries and the abandonment and reconstruction of railroad tracks , telegraph and telephone lines , highways and bridges . The work of constructing the new Croton dam com- menced October 1st , 1892. It calls for a very large quantity of masonry ; in fact , there will be no less than 800,000 cubic yards . In this connection it may be of in- terest to note that it will be the largest block of masonry in the world , excepting the Egyptian pyramids . There are three distinct features of the dam , the spill- way at the north end ; the main stone dam crossing the valley and the embankment at the south end . The spill- way wall is built on the side of the valley , curving up stream from the stone dam ; it is 1,000 feet long , to feet ; high at the end and 150 feet high at its junction with the dam . It is rubble masonry , faced on the water side with cut stone in regular courses and the lower side is in steps of large blocks of stone . A channel for the overflow is excavated in the rock back of the wall leading down to the river below the dam . The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long .

A channel for the overflow is excavated in the rock back of the wall leading down to the river below the dam . The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long . The main stone dam is rubble masonry , faced on both sides , above the surface of the ground , with cut stone in regular courses . It is 297 feet high from the deepest point of the foundation , which is 131 feet below the bed of the river . Its greatest width at the base is 206 feet and the width at the top is 20 feet . At the junction with the core wall according to the original plan it had a height of 230 feet . For the purpose of reaching a point where the core wall would have a lesser height , the Aqueduct Commis- sioners on Sept. 16th , 1896 , on the recommendation of the former Chief Engineer , authorized him to extend the main stone dam 110 feet , in substitution of the embankment and core wall , but even at the point thus reached the core wall would have a height of 200 feet . This extension ma- terially increased the cost of the structure . The embankment was to be 30 feet wide at the top , with sides sloping in the ratio of two horiozntal to one vertical . The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone .

The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone . The core wall in the centre of the embankment was to be four feet higher than the crest of the spillway , six feet wide at the top and increasing to 18 feet at a depth of 136 feet , then same width to the base . The core wall was to be 200 feet high at the junction with the stone dam and 90 feet high at a gate house that is built in the embank- ment , 290 feet from the stone dam . The high end of the core wall had been built in a wide pit , that was a neces- sary excavation for the end of the stone dam , which was 164 feet wide at the base , while the core wall was but 18 feet at its base . The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure .

The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure . Although the contract drawings , upon which the contract was based , indicated " hard rock " at a depth of 75 feet below the bed of the river , yet it was found necessary to excavate the founda- tion pit to a depth of 131 feet before finding a firm foun- dation of hard rock . The character of the stone re- moved varied greatly ; in places it was compact , then di- versified by masses of stone broken up by open , eroded and mud - filled seams , and in places there were belts of disintegrated lime stone . During the progress of the excavation water flowed freely through the seams and several open caves were found in the rock . In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height .

In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height . In the spring of 1901 , this core wall cracked in five places within a length of 100 feet . This caused the writer to believe that some serious disturbance had taken place , as in his opinion the cracks were too close together to be caused by contraction . After close study of the condi- tions , there was no conclusion to be arrived at except that there was a fundamental weakness here , and , therefore , it would be unsafe to proceed with the work . This close study brought to view objectionable features of the plans of the embankment and core wall , the most conspicuous of which were three . First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall .

After close study of the condi- tions , there was no conclusion to be arrived at except that there was a fundamental weakness here , and , therefore , it would be unsafe to proceed with the work . This close study brought to view objectionable features of the plans of the embankment and core wall , the most conspicuous of which were three . First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall .

=== seq 6 ===

Cornell University Library Pamphlet T 462 Modifications of the plan of the new Cro 3 1924 032 873 592 olin , str1 Modifications of the Plan of the New Croton Dam By WILLIAM R. HILL Read before the American Water Works Association at St. Louis , Mo. , June 8th , 1904 Pamphlet 462 21 13861282 ES MODIFICATIONS OF THE PLAN OF THE NEW CROTON DAM . BY WILLIAM R. HILL . The responsibility of the engineer in charge of con- structing dams and reservoirs , is but vaguely appreciated by the public . In view of the many disastrous failures that have occurred , due to faulty plans and poor con- struction , it is made imperative for the engineer to exercise his best powers to insure proper and substantial struc- tures . There is , perhaps , no other field of engineering that develops in the course of construction so many new conditions and unexpected obstacles , and when the en- gineer finds it necessary to make radical changes in the plans , even though involving heavy expenditures and sub- jecting himself to severe criticism , it is his bounden duty to make these changes .

In view of the many disastrous failures that have occurred , due to faulty plans and poor con- struction , it is made imperative for the engineer to exercise his best powers to insure proper and substantial struc- tures . There is , perhaps , no other field of engineering that develops in the course of construction so many new conditions and unexpected obstacles , and when the en- gineer finds it necessary to make radical changes in the plans , even though involving heavy expenditures and sub- jecting himself to severe criticism , it is his bounden duty to make these changes . The writer had the honor of being Chief Engineer of the Aqueduct Commission of the City of New York , from January Ist , 1900 , to October 14th , 1903. During his incumbency the new Croton Dam was under construc- tion . The purpose of this paper is to explain , as briefly as possible , the original plan of this structure and the im- perative necessity of its modification , and to answer a general demand made upon the writer that would seem to indicate a very widespread interest in these rotable changes . Had the work continued under the original plan it might have resulted not only in the failure of the structure itself but have been the cause of immeasurable loss to this great city of its supply of water in addition to an appalling destruction of life and property . The boroughs of Manhattan and Bronx , of an estimated population of 2,200,000 are dependent almost entirely upon the Croton River for their supply of water ; in fact , they have no other supply , except the comparatively small quantity ( 20,000,000 gallons per day ) from the Bronx and Byram Rivers , small as compared with 290,000,000 gallons , the present daily consumption of these two boroughs .

Had the work continued under the original plan it might have resulted not only in the failure of the structure itself but have been the cause of immeasurable loss to this great city of its supply of water in addition to an appalling destruction of life and property . The boroughs of Manhattan and Bronx , of an estimated population of 2,200,000 are dependent almost entirely upon the Croton River for their supply of water ; in fact , they have no other supply , except the comparatively small quantity ( 20,000,000 gallons per day ) from the Bronx and Byram Rivers , small as compared with 290,000,000 gallons , the present daily consumption of these two boroughs . The natural flow of Croton River in dry seasons was judged insufficient to supply the city as early as 1843 , now more than 60 years ago , so Croton Lake of a capac- ity of two billion gallons , was then created by building the old Croton Dam . Since then , from time to time , six other reservoirs , having an aggregate capacity of 40,000,000 , - 000 gallons , have been built on the principal tributaries of the river , above the lake , for the purpose of collecting water in wet seasons , to be discharged into the lake as re- quired for use . The city has no auxiliary supply , and no lakes or rivers that could be used as such in case of an emergency , hence an accident to a reservoir might result in so great a loss of water as to cause a water famine , truly styled one of the world's greatest disasters . The new Croton dam is located about thirty - seven miles from the Central Park reservoirs , it is on the Cro- ton River , about two and one - half miles below the old Croton dam .

The city has no auxiliary supply , and no lakes or rivers that could be used as such in case of an emergency , hence an accident to a reservoir might result in so great a loss of water as to cause a water famine , truly styled one of the world's greatest disasters . The new Croton dam is located about thirty - seven miles from the Central Park reservoirs , it is on the Cro- ton River , about two and one - half miles below the old Croton dam . Its purpose is to enlarge Croton Lake , in- creasing its capacity from two to thirty - two billion gallons and its length from five and one - half to nineteen and three- quarter miles . The old dam will be sumberged , as the flow line will be raised thirty - six feet . The clearing of this great basin for the reservoir , twen- ty miles in length , was in itself an extraordinary under- taking , embracing the clearing of all timber , the removal of three villages , numberless buildings , farm houses and cemeteries and the abandonment and reconstruction of railroad tracks , telegraph and telephone lines , highways and bridges . The work of constructing the new Croton dam com- menced October 1st , 1892. It calls for a very large quantity of masonry ; in fact , there will be no less than 800,000 cubic yards . In this connection it may be of in- terest to note that it will be the largest block of masonry in the world , excepting the Egyptian pyramids . There are three distinct features of the dam , the spill- way at the north end ; the main stone dam crossing the valley and the embankment at the south end .

It calls for a very large quantity of masonry ; in fact , there will be no less than 800,000 cubic yards . In this connection it may be of in- terest to note that it will be the largest block of masonry in the world , excepting the Egyptian pyramids . There are three distinct features of the dam , the spill- way at the north end ; the main stone dam crossing the valley and the embankment at the south end . The spill- way wall is built on the side of the valley , curving up stream from the stone dam ; it is 1,000 feet long , to feet ; high at the end and 150 feet high at its junction with the dam . It is rubble masonry , faced on the water side with cut stone in regular courses and the lower side is in steps of large blocks of stone . A channel for the overflow is excavated in the rock back of the wall leading down to the river below the dam . The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long . The main stone dam is rubble masonry , faced on both sides , above the surface of the ground , with cut stone in regular courses . It is 297 feet high from the deepest point of the foundation , which is 131 feet below the bed of the river . Its greatest width at the base is 206 feet and the width at the top is 20 feet .

The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long . The main stone dam is rubble masonry , faced on both sides , above the surface of the ground , with cut stone in regular courses . It is 297 feet high from the deepest point of the foundation , which is 131 feet below the bed of the river . Its greatest width at the base is 206 feet and the width at the top is 20 feet . At the junction with the core wall according to the original plan it had a height of 230 feet . For the purpose of reaching a point where the core wall would have a lesser height , the Aqueduct Commis- sioners on Sept. 16th , 1896 , on the recommendation of the former Chief Engineer , authorized him to extend the main stone dam 110 feet , in substitution of the embankment and core wall , but even at the point thus reached the core wall would have a height of 200 feet . This extension ma- terially increased the cost of the structure . The embankment was to be 30 feet wide at the top , with sides sloping in the ratio of two horiozntal to one vertical . The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone .

The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone . The core wall in the centre of the embankment was to be four feet higher than the crest of the spillway , six feet wide at the top and increasing to 18 feet at a depth of 136 feet , then same width to the base . The core wall was to be 200 feet high at the junction with the stone dam and 90 feet high at a gate house that is built in the embank- ment , 290 feet from the stone dam . The high end of the core wall had been built in a wide pit , that was a neces- sary excavation for the end of the stone dam , which was 164 feet wide at the base , while the core wall was but 18 feet at its base . The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure .

The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure . Although the contract drawings , upon which the contract was based , indicated " hard rock " at a depth of 75 feet below the bed of the river , yet it was found necessary to excavate the founda- tion pit to a depth of 131 feet before finding a firm foun- dation of hard rock . The character of the stone re- moved varied greatly ; in places it was compact , then di- versified by masses of stone broken up by open , eroded and mud - filled seams , and in places there were belts of disintegrated lime stone . During the progress of the excavation water flowed freely through the seams and several open caves were found in the rock . In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height .

In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height . In the spring of 1901 , this core wall cracked in five places within a length of 100 feet . This caused the writer to believe that some serious disturbance had taken place , as in his opinion the cracks were too close together to be caused by contraction . After close study of the condi- tions , there was no conclusion to be arrived at except that there was a fundamental weakness here , and , therefore , it would be unsafe to proceed with the work . This close study brought to view objectionable features of the plans of the embankment and core wall , the most conspicuous of which were three . First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height .

First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height . As an example , the Amawalk dam , which forms one of the upper Croton reservoirs , while only about half the height , 85 feet , yet has a base even wider than that of this embankment of unprecedented height . And further , this embankment was hazardous because of the unsta- ble nature of its foundation . It was founded over a great refilled pit , which was 360 feet wide at the top , 170 feet at the base and 70 feet deep ; this pit was a necessary ex- cavation for the foundation of the end of the stone dam , which was 164 feet wide at the base as before stated . It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet .

It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet . Considering the height of the wall , and this in artificially placed earth , it could be but an experimental structure , inasmuch as it woud be about twice the height of any heretofore built . The third objection , the double means afforded the water to reach the core wall , this is another serious ob- jection , as the water by starting at the end of the em- bankment in the reservoir and following between the face of the stone dam and the embankment would inevitably reach the core wall . It would be impossible to puddle or other- wise compact the embankment against the dam to pre- vent this , as settlement would surely follow in any em- bankment of this great height . This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have

This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have

=== seq 7 ===

Pamphlet 462 21 13861282 ES MODIFICATIONS OF THE PLAN OF THE NEW CROTON DAM . BY WILLIAM R. HILL . The responsibility of the engineer in charge of con- structing dams and reservoirs , is but vaguely appreciated by the public . In view of the many disastrous failures that have occurred , due to faulty plans and poor con- struction , it is made imperative for the engineer to exercise his best powers to insure proper and substantial struc- tures . There is , perhaps , no other field of engineering that develops in the course of construction so many new conditions and unexpected obstacles , and when the en- gineer finds it necessary to make radical changes in the plans , even though involving heavy expenditures and sub- jecting himself to severe criticism , it is his bounden duty to make these changes . The writer had the honor of being Chief Engineer of the Aqueduct Commission of the City of New York , from January Ist , 1900 , to October 14th , 1903. During his incumbency the new Croton Dam was under construc- tion . The purpose of this paper is to explain , as briefly as possible , the original plan of this structure and the im- perative necessity of its modification , and to answer a general demand made upon the writer that would seem to indicate a very widespread interest in these rotable changes .

The writer had the honor of being Chief Engineer of the Aqueduct Commission of the City of New York , from January Ist , 1900 , to October 14th , 1903. During his incumbency the new Croton Dam was under construc- tion . The purpose of this paper is to explain , as briefly as possible , the original plan of this structure and the im- perative necessity of its modification , and to answer a general demand made upon the writer that would seem to indicate a very widespread interest in these rotable changes . Had the work continued under the original plan it might have resulted not only in the failure of the structure itself but have been the cause of immeasurable loss to this great city of its supply of water in addition to an appalling destruction of life and property . The boroughs of Manhattan and Bronx , of an estimated population of 2,200,000 are dependent almost entirely upon the Croton River for their supply of water ; in fact , they have no other supply , except the comparatively small quantity ( 20,000,000 gallons per day ) from the Bronx and Byram Rivers , small as compared with 290,000,000 gallons , the present daily consumption of these two boroughs . The natural flow of Croton River in dry seasons was judged insufficient to supply the city as early as 1843 , now more than 60 years ago , so Croton Lake of a capac- ity of two billion gallons , was then created by building the old Croton Dam . Since then , from time to time , six other reservoirs , having an aggregate capacity of 40,000,000 , - 000 gallons , have been built on the principal tributaries of the river , above the lake , for the purpose of collecting water in wet seasons , to be discharged into the lake as re- quired for use .

The natural flow of Croton River in dry seasons was judged insufficient to supply the city as early as 1843 , now more than 60 years ago , so Croton Lake of a capac- ity of two billion gallons , was then created by building the old Croton Dam . Since then , from time to time , six other reservoirs , having an aggregate capacity of 40,000,000 , - 000 gallons , have been built on the principal tributaries of the river , above the lake , for the purpose of collecting water in wet seasons , to be discharged into the lake as re- quired for use . The city has no auxiliary supply , and no lakes or rivers that could be used as such in case of an emergency , hence an accident to a reservoir might result in so great a loss of water as to cause a water famine , truly styled one of the world's greatest disasters . The new Croton dam is located about thirty - seven miles from the Central Park reservoirs , it is on the Cro- ton River , about two and one - half miles below the old Croton dam . Its purpose is to enlarge Croton Lake , in- creasing its capacity from two to thirty - two billion gallons and its length from five and one - half to nineteen and three- quarter miles . The old dam will be sumberged , as the flow line will be raised thirty - six feet . The clearing of this great basin for the reservoir , twen- ty miles in length , was in itself an extraordinary under- taking , embracing the clearing of all timber , the removal of three villages , numberless buildings , farm houses and cemeteries and the abandonment and reconstruction of railroad tracks , telegraph and telephone lines , highways and bridges .

The old dam will be sumberged , as the flow line will be raised thirty - six feet . The clearing of this great basin for the reservoir , twen- ty miles in length , was in itself an extraordinary under- taking , embracing the clearing of all timber , the removal of three villages , numberless buildings , farm houses and cemeteries and the abandonment and reconstruction of railroad tracks , telegraph and telephone lines , highways and bridges . The work of constructing the new Croton dam com- menced October 1st , 1892. It calls for a very large quantity of masonry ; in fact , there will be no less than 800,000 cubic yards . In this connection it may be of in- terest to note that it will be the largest block of masonry in the world , excepting the Egyptian pyramids . There are three distinct features of the dam , the spill- way at the north end ; the main stone dam crossing the valley and the embankment at the south end . The spill- way wall is built on the side of the valley , curving up stream from the stone dam ; it is 1,000 feet long , to feet ; high at the end and 150 feet high at its junction with the dam . It is rubble masonry , faced on the water side with cut stone in regular courses and the lower side is in steps of large blocks of stone . A channel for the overflow is excavated in the rock back of the wall leading down to the river below the dam . The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long .

A channel for the overflow is excavated in the rock back of the wall leading down to the river below the dam . The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long . The main stone dam is rubble masonry , faced on both sides , above the surface of the ground , with cut stone in regular courses . It is 297 feet high from the deepest point of the foundation , which is 131 feet below the bed of the river . Its greatest width at the base is 206 feet and the width at the top is 20 feet . At the junction with the core wall according to the original plan it had a height of 230 feet . For the purpose of reaching a point where the core wall would have a lesser height , the Aqueduct Commis- sioners on Sept. 16th , 1896 , on the recommendation of the former Chief Engineer , authorized him to extend the main stone dam 110 feet , in substitution of the embankment and core wall , but even at the point thus reached the core wall would have a height of 200 feet . This extension ma- terially increased the cost of the structure . The embankment was to be 30 feet wide at the top , with sides sloping in the ratio of two horiozntal to one vertical . The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone .

The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone . The core wall in the centre of the embankment was to be four feet higher than the crest of the spillway , six feet wide at the top and increasing to 18 feet at a depth of 136 feet , then same width to the base . The core wall was to be 200 feet high at the junction with the stone dam and 90 feet high at a gate house that is built in the embank- ment , 290 feet from the stone dam . The high end of the core wall had been built in a wide pit , that was a neces- sary excavation for the end of the stone dam , which was 164 feet wide at the base , while the core wall was but 18 feet at its base . The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure .

The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure . Although the contract drawings , upon which the contract was based , indicated " hard rock " at a depth of 75 feet below the bed of the river , yet it was found necessary to excavate the founda- tion pit to a depth of 131 feet before finding a firm foun- dation of hard rock . The character of the stone re- moved varied greatly ; in places it was compact , then di- versified by masses of stone broken up by open , eroded and mud - filled seams , and in places there were belts of disintegrated lime stone . During the progress of the excavation water flowed freely through the seams and several open caves were found in the rock . In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height .

In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height . In the spring of 1901 , this core wall cracked in five places within a length of 100 feet . This caused the writer to believe that some serious disturbance had taken place , as in his opinion the cracks were too close together to be caused by contraction . After close study of the condi- tions , there was no conclusion to be arrived at except that there was a fundamental weakness here , and , therefore , it would be unsafe to proceed with the work . This close study brought to view objectionable features of the plans of the embankment and core wall , the most conspicuous of which were three . First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height .

First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height . As an example , the Amawalk dam , which forms one of the upper Croton reservoirs , while only about half the height , 85 feet , yet has a base even wider than that of this embankment of unprecedented height . And further , this embankment was hazardous because of the unsta- ble nature of its foundation . It was founded over a great refilled pit , which was 360 feet wide at the top , 170 feet at the base and 70 feet deep ; this pit was a necessary ex- cavation for the foundation of the end of the stone dam , which was 164 feet wide at the base as before stated . It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet .

It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet . Considering the height of the wall , and this in artificially placed earth , it could be but an experimental structure , inasmuch as it woud be about twice the height of any heretofore built . The third objection , the double means afforded the water to reach the core wall , this is another serious ob- jection , as the water by starting at the end of the em- bankment in the reservoir and following between the face of the stone dam and the embankment would inevitably reach the core wall . It would be impossible to puddle or other- wise compact the embankment against the dam to pre- vent this , as settlement would surely follow in any em- bankment of this great height . This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have STONE DAM البلد TOP OF 290 - FEET_ .

This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have STONE DAM البلد TOP OF 290 - FEET_ . CORE WALL MARCH 1ST 1901 EMOVED DISINTEGRATED FLIMESTONE SHATTERED LIME STONE THE NEW CROTON DAM LONGITUDINAL SECTION ON AXIS OF DAM , SHOWING CORE WALL REMOVED AND ITS DEFECTIVE LIME STONE FOUNDATION , WHICH HAS BEEN EXCAVATED FOR THE EXTENSION OF THE DAM . AK GATE HOUSE . CHAMBERS TO BE REMODELED AND REINFORCED

=== seq 8 ===

MODIFICATIONS OF THE PLAN OF THE NEW CROTON DAM . BY WILLIAM R. HILL . The responsibility of the engineer in charge of con- structing dams and reservoirs , is but vaguely appreciated by the public . In view of the many disastrous failures that have occurred , due to faulty plans and poor con- struction , it is made imperative for the engineer to exercise his best powers to insure proper and substantial struc- tures . There is , perhaps , no other field of engineering that develops in the course of construction so many new conditions and unexpected obstacles , and when the en- gineer finds it necessary to make radical changes in the plans , even though involving heavy expenditures and sub- jecting himself to severe criticism , it is his bounden duty to make these changes . The writer had the honor of being Chief Engineer of the Aqueduct Commission of the City of New York , from January Ist , 1900 , to October 14th , 1903.

There is , perhaps , no other field of engineering that develops in the course of construction so many new conditions and unexpected obstacles , and when the en- gineer finds it necessary to make radical changes in the plans , even though involving heavy expenditures and sub- jecting himself to severe criticism , it is his bounden duty to make these changes . The writer had the honor of being Chief Engineer of the Aqueduct Commission of the City of New York , from January Ist , 1900 , to October 14th , 1903. During his incumbency the new Croton Dam was under construc- tion . The purpose of this paper is to explain , as briefly as possible , the original plan of this structure and the im- perative necessity of its modification , and to answer a general demand made upon the writer that would seem to indicate a very widespread interest in these rotable changes . Had the work continued under the original plan it might have resulted not only in the failure of the structure itself but have been the cause of immeasurable loss to this great city of its supply of water in addition to an appalling destruction of life and property . The boroughs of Manhattan and Bronx , of an estimated population of 2,200,000 are dependent almost entirely upon the Croton River for their supply of water ; in fact , they have no other supply , except the comparatively small quantity ( 20,000,000 gallons per day ) from the Bronx and Byram Rivers , small as compared with 290,000,000 gallons , the present daily consumption of these two boroughs . The natural flow of Croton River in dry seasons was judged insufficient to supply the city as early as 1843 , now more than 60 years ago , so Croton Lake of a capac- ity of two billion gallons , was then created by building the old Croton Dam .

The boroughs of Manhattan and Bronx , of an estimated population of 2,200,000 are dependent almost entirely upon the Croton River for their supply of water ; in fact , they have no other supply , except the comparatively small quantity ( 20,000,000 gallons per day ) from the Bronx and Byram Rivers , small as compared with 290,000,000 gallons , the present daily consumption of these two boroughs . The natural flow of Croton River in dry seasons was judged insufficient to supply the city as early as 1843 , now more than 60 years ago , so Croton Lake of a capac- ity of two billion gallons , was then created by building the old Croton Dam . Since then , from time to time , six other reservoirs , having an aggregate capacity of 40,000,000 , - 000 gallons , have been built on the principal tributaries of the river , above the lake , for the purpose of collecting water in wet seasons , to be discharged into the lake as re- quired for use . The city has no auxiliary supply , and no lakes or rivers that could be used as such in case of an emergency , hence an accident to a reservoir might result in so great a loss of water as to cause a water famine , truly styled one of the world's greatest disasters . The new Croton dam is located about thirty - seven miles from the Central Park reservoirs , it is on the Cro- ton River , about two and one - half miles below the old Croton dam . Its purpose is to enlarge Croton Lake , in- creasing its capacity from two to thirty - two billion gallons and its length from five and one - half to nineteen and three- quarter miles .

The city has no auxiliary supply , and no lakes or rivers that could be used as such in case of an emergency , hence an accident to a reservoir might result in so great a loss of water as to cause a water famine , truly styled one of the world's greatest disasters . The new Croton dam is located about thirty - seven miles from the Central Park reservoirs , it is on the Cro- ton River , about two and one - half miles below the old Croton dam . Its purpose is to enlarge Croton Lake , in- creasing its capacity from two to thirty - two billion gallons and its length from five and one - half to nineteen and three- quarter miles . The old dam will be sumberged , as the flow line will be raised thirty - six feet . The clearing of this great basin for the reservoir , twen- ty miles in length , was in itself an extraordinary under- taking , embracing the clearing of all timber , the removal of three villages , numberless buildings , farm houses and cemeteries and the abandonment and reconstruction of railroad tracks , telegraph and telephone lines , highways and bridges . The work of constructing the new Croton dam com- menced October 1st , 1892. It calls for a very large quantity of masonry ; in fact , there will be no less than 800,000 cubic yards . In this connection it may be of in- terest to note that it will be the largest block of masonry in the world , excepting the Egyptian pyramids . There are three distinct features of the dam , the spill- way at the north end ; the main stone dam crossing the valley and the embankment at the south end .

It calls for a very large quantity of masonry ; in fact , there will be no less than 800,000 cubic yards . In this connection it may be of in- terest to note that it will be the largest block of masonry in the world , excepting the Egyptian pyramids . There are three distinct features of the dam , the spill- way at the north end ; the main stone dam crossing the valley and the embankment at the south end . The spill- way wall is built on the side of the valley , curving up stream from the stone dam ; it is 1,000 feet long , to feet ; high at the end and 150 feet high at its junction with the dam . It is rubble masonry , faced on the water side with cut stone in regular courses and the lower side is in steps of large blocks of stone . A channel for the overflow is excavated in the rock back of the wall leading down to the river below the dam . The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long . The main stone dam is rubble masonry , faced on both sides , above the surface of the ground , with cut stone in regular courses . It is 297 feet high from the deepest point of the foundation , which is 131 feet below the bed of the river . Its greatest width at the base is 206 feet and the width at the top is 20 feet .

The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long . The main stone dam is rubble masonry , faced on both sides , above the surface of the ground , with cut stone in regular courses . It is 297 feet high from the deepest point of the foundation , which is 131 feet below the bed of the river . Its greatest width at the base is 206 feet and the width at the top is 20 feet . At the junction with the core wall according to the original plan it had a height of 230 feet . For the purpose of reaching a point where the core wall would have a lesser height , the Aqueduct Commis- sioners on Sept. 16th , 1896 , on the recommendation of the former Chief Engineer , authorized him to extend the main stone dam 110 feet , in substitution of the embankment and core wall , but even at the point thus reached the core wall would have a height of 200 feet . This extension ma- terially increased the cost of the structure . The embankment was to be 30 feet wide at the top , with sides sloping in the ratio of two horiozntal to one vertical . The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone .

The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone . The core wall in the centre of the embankment was to be four feet higher than the crest of the spillway , six feet wide at the top and increasing to 18 feet at a depth of 136 feet , then same width to the base . The core wall was to be 200 feet high at the junction with the stone dam and 90 feet high at a gate house that is built in the embank- ment , 290 feet from the stone dam . The high end of the core wall had been built in a wide pit , that was a neces- sary excavation for the end of the stone dam , which was 164 feet wide at the base , while the core wall was but 18 feet at its base . The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure .

The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure . Although the contract drawings , upon which the contract was based , indicated " hard rock " at a depth of 75 feet below the bed of the river , yet it was found necessary to excavate the founda- tion pit to a depth of 131 feet before finding a firm foun- dation of hard rock . The character of the stone re- moved varied greatly ; in places it was compact , then di- versified by masses of stone broken up by open , eroded and mud - filled seams , and in places there were belts of disintegrated lime stone . During the progress of the excavation water flowed freely through the seams and several open caves were found in the rock . In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height .

In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height . In the spring of 1901 , this core wall cracked in five places within a length of 100 feet . This caused the writer to believe that some serious disturbance had taken place , as in his opinion the cracks were too close together to be caused by contraction . After close study of the condi- tions , there was no conclusion to be arrived at except that there was a fundamental weakness here , and , therefore , it would be unsafe to proceed with the work . This close study brought to view objectionable features of the plans of the embankment and core wall , the most conspicuous of which were three . First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height .

First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height . As an example , the Amawalk dam , which forms one of the upper Croton reservoirs , while only about half the height , 85 feet , yet has a base even wider than that of this embankment of unprecedented height . And further , this embankment was hazardous because of the unsta- ble nature of its foundation . It was founded over a great refilled pit , which was 360 feet wide at the top , 170 feet at the base and 70 feet deep ; this pit was a necessary ex- cavation for the foundation of the end of the stone dam , which was 164 feet wide at the base as before stated . It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet .

It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet . Considering the height of the wall , and this in artificially placed earth , it could be but an experimental structure , inasmuch as it woud be about twice the height of any heretofore built . The third objection , the double means afforded the water to reach the core wall , this is another serious ob- jection , as the water by starting at the end of the em- bankment in the reservoir and following between the face of the stone dam and the embankment would inevitably reach the core wall . It would be impossible to puddle or other- wise compact the embankment against the dam to pre- vent this , as settlement would surely follow in any em- bankment of this great height . This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have STONE DAM البلد TOP OF 290 - FEET_ .

This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have STONE DAM البلد TOP OF 290 - FEET_ . CORE WALL MARCH 1ST 1901 EMOVED DISINTEGRATED FLIMESTONE SHATTERED LIME STONE THE NEW CROTON DAM LONGITUDINAL SECTION ON AXIS OF DAM , SHOWING CORE WALL REMOVED AND ITS DEFECTIVE LIME STONE FOUNDATION , WHICH HAS BEEN EXCAVATED FOR THE EXTENSION OF THE DAM . AK GATE HOUSE . CHAMBERS TO BE REMODELED AND REINFORCED in ordinary cases , where the wall below the original sur- face of the ground is in a narrow trench and protected by original soil . It would be useless to consider any proposi- tion to increase the width of the embankment , because the means afforded the water to reach the core wall along the face of the dam would always remain ; this is a most dan- gerous feature , as the core wall would not have sufficient weight or strength to resist the pressure of the water that would come against it . A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure . Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall .

A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure . Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall . Such a structure can not be regarded as anything but an experiment . It is abnormal and unprecedented in all its dangerous features . The engineer might apply in vain to science for aid in computing the efficiency of such a structures ; he could get no light , for he could find not even the slightest guaranty of safety in a structure so built . The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish . Thus , the writer , was thoroughly convinced that a change in the plan of the structure at this point was nec- essary . Thereupon he recommended to the Aqueduct Commissioners that this entire section of the embank- ment and core wall to the gatehouse be removed and the stone dam extended in its place .

The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish . Thus , the writer , was thoroughly convinced that a change in the plan of the structure at this point was nec- essary . Thereupon he recommended to the Aqueduct Commissioners that this entire section of the embank- ment and core wall to the gatehouse be removed and the stone dam extended in its place . But while maintaining that the conditions allowed of no other conclusion , he

=== seq 9 ===

and Byram Rivers , small as compared with 290,000,000 gallons , the present daily consumption of these two boroughs . The natural flow of Croton River in dry seasons was judged insufficient to supply the city as early as 1843 , now more than 60 years ago , so Croton Lake of a capac- ity of two billion gallons , was then created by building the old Croton Dam . Since then , from time to time , six other reservoirs , having an aggregate capacity of 40,000,000 , - 000 gallons , have been built on the principal tributaries of the river , above the lake , for the purpose of collecting water in wet seasons , to be discharged into the lake as re- quired for use . The city has no auxiliary supply , and no lakes or rivers that could be used as such in case of an emergency , hence an accident to a reservoir might result in so great a loss of water as to cause a water famine , truly styled one of the world's greatest disasters .

Since then , from time to time , six other reservoirs , having an aggregate capacity of 40,000,000 , - 000 gallons , have been built on the principal tributaries of the river , above the lake , for the purpose of collecting water in wet seasons , to be discharged into the lake as re- quired for use . The city has no auxiliary supply , and no lakes or rivers that could be used as such in case of an emergency , hence an accident to a reservoir might result in so great a loss of water as to cause a water famine , truly styled one of the world's greatest disasters . The new Croton dam is located about thirty - seven miles from the Central Park reservoirs , it is on the Cro- ton River , about two and one - half miles below the old Croton dam . Its purpose is to enlarge Croton Lake , in- creasing its capacity from two to thirty - two billion gallons and its length from five and one - half to nineteen and three- quarter miles . The old dam will be sumberged , as the flow line will be raised thirty - six feet . The clearing of this great basin for the reservoir , twen- ty miles in length , was in itself an extraordinary under- taking , embracing the clearing of all timber , the removal of three villages , numberless buildings , farm houses and cemeteries and the abandonment and reconstruction of railroad tracks , telegraph and telephone lines , highways and bridges . The work of constructing the new Croton dam com- menced October 1st , 1892. It calls for a very large quantity of masonry ; in fact , there will be no less than 800,000 cubic yards .

The clearing of this great basin for the reservoir , twen- ty miles in length , was in itself an extraordinary under- taking , embracing the clearing of all timber , the removal of three villages , numberless buildings , farm houses and cemeteries and the abandonment and reconstruction of railroad tracks , telegraph and telephone lines , highways and bridges . The work of constructing the new Croton dam com- menced October 1st , 1892. It calls for a very large quantity of masonry ; in fact , there will be no less than 800,000 cubic yards . In this connection it may be of in- terest to note that it will be the largest block of masonry in the world , excepting the Egyptian pyramids . There are three distinct features of the dam , the spill- way at the north end ; the main stone dam crossing the valley and the embankment at the south end . The spill- way wall is built on the side of the valley , curving up stream from the stone dam ; it is 1,000 feet long , to feet ; high at the end and 150 feet high at its junction with the dam . It is rubble masonry , faced on the water side with cut stone in regular courses and the lower side is in steps of large blocks of stone . A channel for the overflow is excavated in the rock back of the wall leading down to the river below the dam . The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long .

A channel for the overflow is excavated in the rock back of the wall leading down to the river below the dam . The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long . The main stone dam is rubble masonry , faced on both sides , above the surface of the ground , with cut stone in regular courses . It is 297 feet high from the deepest point of the foundation , which is 131 feet below the bed of the river . Its greatest width at the base is 206 feet and the width at the top is 20 feet . At the junction with the core wall according to the original plan it had a height of 230 feet . For the purpose of reaching a point where the core wall would have a lesser height , the Aqueduct Commis- sioners on Sept. 16th , 1896 , on the recommendation of the former Chief Engineer , authorized him to extend the main stone dam 110 feet , in substitution of the embankment and core wall , but even at the point thus reached the core wall would have a height of 200 feet . This extension ma- terially increased the cost of the structure . The embankment was to be 30 feet wide at the top , with sides sloping in the ratio of two horiozntal to one vertical . The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone .

The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone . The core wall in the centre of the embankment was to be four feet higher than the crest of the spillway , six feet wide at the top and increasing to 18 feet at a depth of 136 feet , then same width to the base . The core wall was to be 200 feet high at the junction with the stone dam and 90 feet high at a gate house that is built in the embank- ment , 290 feet from the stone dam . The high end of the core wall had been built in a wide pit , that was a neces- sary excavation for the end of the stone dam , which was 164 feet wide at the base , while the core wall was but 18 feet at its base . The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure .

The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure . Although the contract drawings , upon which the contract was based , indicated " hard rock " at a depth of 75 feet below the bed of the river , yet it was found necessary to excavate the founda- tion pit to a depth of 131 feet before finding a firm foun- dation of hard rock . The character of the stone re- moved varied greatly ; in places it was compact , then di- versified by masses of stone broken up by open , eroded and mud - filled seams , and in places there were belts of disintegrated lime stone . During the progress of the excavation water flowed freely through the seams and several open caves were found in the rock . In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height .

In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height . In the spring of 1901 , this core wall cracked in five places within a length of 100 feet . This caused the writer to believe that some serious disturbance had taken place , as in his opinion the cracks were too close together to be caused by contraction . After close study of the condi- tions , there was no conclusion to be arrived at except that there was a fundamental weakness here , and , therefore , it would be unsafe to proceed with the work . This close study brought to view objectionable features of the plans of the embankment and core wall , the most conspicuous of which were three . First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height .

First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height . As an example , the Amawalk dam , which forms one of the upper Croton reservoirs , while only about half the height , 85 feet , yet has a base even wider than that of this embankment of unprecedented height . And further , this embankment was hazardous because of the unsta- ble nature of its foundation . It was founded over a great refilled pit , which was 360 feet wide at the top , 170 feet at the base and 70 feet deep ; this pit was a necessary ex- cavation for the foundation of the end of the stone dam , which was 164 feet wide at the base as before stated . It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet .

It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet . Considering the height of the wall , and this in artificially placed earth , it could be but an experimental structure , inasmuch as it woud be about twice the height of any heretofore built . The third objection , the double means afforded the water to reach the core wall , this is another serious ob- jection , as the water by starting at the end of the em- bankment in the reservoir and following between the face of the stone dam and the embankment would inevitably reach the core wall . It would be impossible to puddle or other- wise compact the embankment against the dam to pre- vent this , as settlement would surely follow in any em- bankment of this great height . This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have STONE DAM البلد TOP OF 290 - FEET_ .

This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have STONE DAM البلد TOP OF 290 - FEET_ . CORE WALL MARCH 1ST 1901 EMOVED DISINTEGRATED FLIMESTONE SHATTERED LIME STONE THE NEW CROTON DAM LONGITUDINAL SECTION ON AXIS OF DAM , SHOWING CORE WALL REMOVED AND ITS DEFECTIVE LIME STONE FOUNDATION , WHICH HAS BEEN EXCAVATED FOR THE EXTENSION OF THE DAM . AK GATE HOUSE . CHAMBERS TO BE REMODELED AND REINFORCED in ordinary cases , where the wall below the original sur- face of the ground is in a narrow trench and protected by original soil . It would be useless to consider any proposi- tion to increase the width of the embankment , because the means afforded the water to reach the core wall along the face of the dam would always remain ; this is a most dan- gerous feature , as the core wall would not have sufficient weight or strength to resist the pressure of the water that would come against it . A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure . Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall .

A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure . Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall . Such a structure can not be regarded as anything but an experiment . It is abnormal and unprecedented in all its dangerous features . The engineer might apply in vain to science for aid in computing the efficiency of such a structures ; he could get no light , for he could find not even the slightest guaranty of safety in a structure so built . The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish . Thus , the writer , was thoroughly convinced that a change in the plan of the structure at this point was nec- essary . Thereupon he recommended to the Aqueduct Commissioners that this entire section of the embank- ment and core wall to the gatehouse be removed and the stone dam extended in its place .

The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish . Thus , the writer , was thoroughly convinced that a change in the plan of the structure at this point was nec- essary . Thereupon he recommended to the Aqueduct Commissioners that this entire section of the embank- ment and core wall to the gatehouse be removed and the stone dam extended in its place . But while maintaining that the conditions allowed of no other conclusion , he recommended that a committee of three engineers be ap- pointed to pass upon a question of so vital and wide- spread importance . The Commissioners after personal investigation agreed in this and appointed a committee of expert engineers consisting of Messrs . J. J. R. Croes , Past President of the American Society of Civil Engineers ; Edwin F. Smith , Chief Engineer of the Schuvlkill Navigation Company and Elnathan Sweet , former Engineer of the State of New York . The committee after making an investiga- tion reported unanimously recommending this extension of the stone dam to the gatehouse . The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon .

The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon . On April 16 , 1902 , the Aqueduct Commissioners resolved to remove the em- bankment and core wall and to continue the main stone dam to the gatehouse . The estimated cost to complete the embankment and core wall under the original plan was $ 145,233.00 , while the preliminary estimate of the cost to remove the em- bankment and core wall and extend the main stone dam is $ 635,700 . The difference $ 490,467 being due to this modification , yet there will be a further increase because of the condition of the natural foundation of the core wall , as hereinafter described . In considering this esti- mate one should not loose sight of the fact that there has been a loss sustained of about $ 80,000 , the cost of that part of the core wall that had to be thus abandoned . In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge .

In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge .

=== seq 10 ===

dam . It is rubble masonry , faced on the water side with cut stone in regular courses and the lower side is in steps of large blocks of stone . A channel for the overflow is excavated in the rock back of the wall leading down to the river below the dam . The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long . The main stone dam is rubble masonry , faced on both sides , above the surface of the ground , with cut stone in regular courses . It is 297 feet high from the deepest point of the foundation , which is 131 feet below the bed of the river . Its greatest width at the base is 206 feet and the width at the top is 20 feet . At the junction with the core wall according to the original plan it had a height of 230 feet .

The main stone dam is rubble masonry , faced on both sides , above the surface of the ground , with cut stone in regular courses . It is 297 feet high from the deepest point of the foundation , which is 131 feet below the bed of the river . Its greatest width at the base is 206 feet and the width at the top is 20 feet . At the junction with the core wall according to the original plan it had a height of 230 feet . For the purpose of reaching a point where the core wall would have a lesser height , the Aqueduct Commis- sioners on Sept. 16th , 1896 , on the recommendation of the former Chief Engineer , authorized him to extend the main stone dam 110 feet , in substitution of the embankment and core wall , but even at the point thus reached the core wall would have a height of 200 feet . This extension ma- terially increased the cost of the structure . The embankment was to be 30 feet wide at the top , with sides sloping in the ratio of two horiozntal to one vertical . The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone . The core wall in the centre of the embankment was to be four feet higher than the crest of the spillway , six feet wide at the top and increasing to 18 feet at a depth of 136 feet , then same width to the base .

The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone . The core wall in the centre of the embankment was to be four feet higher than the crest of the spillway , six feet wide at the top and increasing to 18 feet at a depth of 136 feet , then same width to the base . The core wall was to be 200 feet high at the junction with the stone dam and 90 feet high at a gate house that is built in the embank- ment , 290 feet from the stone dam . The high end of the core wall had been built in a wide pit , that was a neces- sary excavation for the end of the stone dam , which was 164 feet wide at the base , while the core wall was but 18 feet at its base . The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure .

The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure . Although the contract drawings , upon which the contract was based , indicated " hard rock " at a depth of 75 feet below the bed of the river , yet it was found necessary to excavate the founda- tion pit to a depth of 131 feet before finding a firm foun- dation of hard rock . The character of the stone re- moved varied greatly ; in places it was compact , then di- versified by masses of stone broken up by open , eroded and mud - filled seams , and in places there were belts of disintegrated lime stone . During the progress of the excavation water flowed freely through the seams and several open caves were found in the rock . In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height .

In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height . In the spring of 1901 , this core wall cracked in five places within a length of 100 feet . This caused the writer to believe that some serious disturbance had taken place , as in his opinion the cracks were too close together to be caused by contraction . After close study of the condi- tions , there was no conclusion to be arrived at except that there was a fundamental weakness here , and , therefore , it would be unsafe to proceed with the work . This close study brought to view objectionable features of the plans of the embankment and core wall , the most conspicuous of which were three . First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height .

First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height . As an example , the Amawalk dam , which forms one of the upper Croton reservoirs , while only about half the height , 85 feet , yet has a base even wider than that of this embankment of unprecedented height . And further , this embankment was hazardous because of the unsta- ble nature of its foundation . It was founded over a great refilled pit , which was 360 feet wide at the top , 170 feet at the base and 70 feet deep ; this pit was a necessary ex- cavation for the foundation of the end of the stone dam , which was 164 feet wide at the base as before stated . It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet .

It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet . Considering the height of the wall , and this in artificially placed earth , it could be but an experimental structure , inasmuch as it woud be about twice the height of any heretofore built . The third objection , the double means afforded the water to reach the core wall , this is another serious ob- jection , as the water by starting at the end of the em- bankment in the reservoir and following between the face of the stone dam and the embankment would inevitably reach the core wall . It would be impossible to puddle or other- wise compact the embankment against the dam to pre- vent this , as settlement would surely follow in any em- bankment of this great height . This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have STONE DAM البلد TOP OF 290 - FEET_ .

This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have STONE DAM البلد TOP OF 290 - FEET_ . CORE WALL MARCH 1ST 1901 EMOVED DISINTEGRATED FLIMESTONE SHATTERED LIME STONE THE NEW CROTON DAM LONGITUDINAL SECTION ON AXIS OF DAM , SHOWING CORE WALL REMOVED AND ITS DEFECTIVE LIME STONE FOUNDATION , WHICH HAS BEEN EXCAVATED FOR THE EXTENSION OF THE DAM . AK GATE HOUSE . CHAMBERS TO BE REMODELED AND REINFORCED in ordinary cases , where the wall below the original sur- face of the ground is in a narrow trench and protected by original soil . It would be useless to consider any proposi- tion to increase the width of the embankment , because the means afforded the water to reach the core wall along the face of the dam would always remain ; this is a most dan- gerous feature , as the core wall would not have sufficient weight or strength to resist the pressure of the water that would come against it . A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure . Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall .

A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure . Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall . Such a structure can not be regarded as anything but an experiment . It is abnormal and unprecedented in all its dangerous features . The engineer might apply in vain to science for aid in computing the efficiency of such a structures ; he could get no light , for he could find not even the slightest guaranty of safety in a structure so built . The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish . Thus , the writer , was thoroughly convinced that a change in the plan of the structure at this point was nec- essary . Thereupon he recommended to the Aqueduct Commissioners that this entire section of the embank- ment and core wall to the gatehouse be removed and the stone dam extended in its place .

The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish . Thus , the writer , was thoroughly convinced that a change in the plan of the structure at this point was nec- essary . Thereupon he recommended to the Aqueduct Commissioners that this entire section of the embank- ment and core wall to the gatehouse be removed and the stone dam extended in its place . But while maintaining that the conditions allowed of no other conclusion , he recommended that a committee of three engineers be ap- pointed to pass upon a question of so vital and wide- spread importance . The Commissioners after personal investigation agreed in this and appointed a committee of expert engineers consisting of Messrs . J. J. R. Croes , Past President of the American Society of Civil Engineers ; Edwin F. Smith , Chief Engineer of the Schuvlkill Navigation Company and Elnathan Sweet , former Engineer of the State of New York . The committee after making an investiga- tion reported unanimously recommending this extension of the stone dam to the gatehouse . The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon .

The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon . On April 16 , 1902 , the Aqueduct Commissioners resolved to remove the em- bankment and core wall and to continue the main stone dam to the gatehouse . The estimated cost to complete the embankment and core wall under the original plan was $ 145,233.00 , while the preliminary estimate of the cost to remove the em- bankment and core wall and extend the main stone dam is $ 635,700 . The difference $ 490,467 being due to this modification , yet there will be a further increase because of the condition of the natural foundation of the core wall , as hereinafter described . In considering this esti- mate one should not loose sight of the fact that there has been a loss sustained of about $ 80,000 , the cost of that part of the core wall that had to be thus abandoned . In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge .

In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge . The hardest of this stone was full of eroded , open and mud - filled seams , the existence of mud being evidence that these seams had acted as passageways for water . Under date of April 1 , 1903 , Prof. Burr , who had con- curred in the condemnation of the wall , reported to Mayor Low as to the foundation as follows : " It is most fortunate that the core wall has been removed so as to dis- close the actual situation and thus remove what would have been a source of gravest danger to the completed embankment structure as originally planned . " Prof. J. E. Kemp , of Columbia University and Prof. J. J. Stevenson , of New York University , both geologists , were retained to investigate the locality affected . They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found .

They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found . The removal of this soft rock and the replacing it with masonry has again materially in- creased the cost of the structure . The work of building this masonry is now in progress . Another important change of plan is that of the gate- house , above referred to . This gatehouse is located in the embankment outside of the core wall . It is well up on the slope of the valley , its base being about 100 feet higher than the bed of the river . The substructure of this gatehouse is described as follows : It has four water chambers , 74 feet deep and about 12 feet square . Two on the southerly side of the structure are to control the flow of the water in the old Croton aqueduct which passes through this gatehouse . The other two on the northerly side , are to control the flow of water direct from the res- ervoir to the old aqueduct below the dam . These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base .

These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base . These walls which had been built to a height of fifty

=== seq 11 ===

along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases . The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly be- yond the end of the structure . Although the contract drawings , upon which the contract was based , indicated " hard rock " at a depth of 75 feet below the bed of the river , yet it was found necessary to excavate the founda- tion pit to a depth of 131 feet before finding a firm foun- dation of hard rock . The character of the stone re- moved varied greatly ; in places it was compact , then di- versified by masses of stone broken up by open , eroded and mud - filled seams , and in places there were belts of disintegrated lime stone . During the progress of the excavation water flowed freely through the seams and several open caves were found in the rock .

Although the contract drawings , upon which the contract was based , indicated " hard rock " at a depth of 75 feet below the bed of the river , yet it was found necessary to excavate the founda- tion pit to a depth of 131 feet before finding a firm foun- dation of hard rock . The character of the stone re- moved varied greatly ; in places it was compact , then di- versified by masses of stone broken up by open , eroded and mud - filled seams , and in places there were belts of disintegrated lime stone . During the progress of the excavation water flowed freely through the seams and several open caves were found in the rock . In conse- quence of this great additional depth , it was also neces- sary to greatly increase the width of the base of the dam . Thus again the cost was materially increased because of the additional quantity of excavation and masonry . Before the writer assumed the responsibility of this work , the foundation of the stone dam had been com- pleted to the surface of the ground and the core wall had been completed , excepting the stretch between the stone dam and the gate house , which lacked about 60 feet of its height . In the spring of 1901 , this core wall cracked in five places within a length of 100 feet . This caused the writer to believe that some serious disturbance had taken place , as in his opinion the cracks were too close together to be caused by contraction . After close study of the condi- tions , there was no conclusion to be arrived at except that there was a fundamental weakness here , and , therefore , it would be unsafe to proceed with the work .

In the spring of 1901 , this core wall cracked in five places within a length of 100 feet . This caused the writer to believe that some serious disturbance had taken place , as in his opinion the cracks were too close together to be caused by contraction . After close study of the condi- tions , there was no conclusion to be arrived at except that there was a fundamental weakness here , and , therefore , it would be unsafe to proceed with the work . This close study brought to view objectionable features of the plans of the embankment and core wall , the most conspicuous of which were three . First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height . As an example , the Amawalk dam , which forms one of the upper Croton reservoirs , while only about half the height , 85 feet , yet has a base even wider than that of this embankment of unprecedented height . And further , this embankment was hazardous because of the unsta- ble nature of its foundation . It was founded over a great refilled pit , which was 360 feet wide at the top , 170 feet at the base and 70 feet deep ; this pit was a necessary ex- cavation for the foundation of the end of the stone dam , which was 164 feet wide at the base as before stated .

And further , this embankment was hazardous because of the unsta- ble nature of its foundation . It was founded over a great refilled pit , which was 360 feet wide at the top , 170 feet at the base and 70 feet deep ; this pit was a necessary ex- cavation for the foundation of the end of the stone dam , which was 164 feet wide at the base as before stated . It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet . Considering the height of the wall , and this in artificially placed earth , it could be but an experimental structure , inasmuch as it woud be about twice the height of any heretofore built . The third objection , the double means afforded the water to reach the core wall , this is another serious ob- jection , as the water by starting at the end of the em- bankment in the reservoir and following between the face of the stone dam and the embankment would inevitably reach the core wall . It would be impossible to puddle or other- wise compact the embankment against the dam to pre- vent this , as settlement would surely follow in any em- bankment of this great height . This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall .

It would be impossible to puddle or other- wise compact the embankment against the dam to pre- vent this , as settlement would surely follow in any em- bankment of this great height . This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have STONE DAM البلد TOP OF 290 - FEET_ . CORE WALL MARCH 1ST 1901 EMOVED DISINTEGRATED FLIMESTONE SHATTERED LIME STONE THE NEW CROTON DAM LONGITUDINAL SECTION ON AXIS OF DAM , SHOWING CORE WALL REMOVED AND ITS DEFECTIVE LIME STONE FOUNDATION , WHICH HAS BEEN EXCAVATED FOR THE EXTENSION OF THE DAM . AK GATE HOUSE . CHAMBERS TO BE REMODELED AND REINFORCED in ordinary cases , where the wall below the original sur- face of the ground is in a narrow trench and protected by original soil . It would be useless to consider any proposi- tion to increase the width of the embankment , because the means afforded the water to reach the core wall along the face of the dam would always remain ; this is a most dan- gerous feature , as the core wall would not have sufficient weight or strength to resist the pressure of the water that would come against it . A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure .

It would be useless to consider any proposi- tion to increase the width of the embankment , because the means afforded the water to reach the core wall along the face of the dam would always remain ; this is a most dan- gerous feature , as the core wall would not have sufficient weight or strength to resist the pressure of the water that would come against it . A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure . Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall . Such a structure can not be regarded as anything but an experiment . It is abnormal and unprecedented in all its dangerous features . The engineer might apply in vain to science for aid in computing the efficiency of such a structures ; he could get no light , for he could find not even the slightest guaranty of safety in a structure so built . The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish .

The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish . Thus , the writer , was thoroughly convinced that a change in the plan of the structure at this point was nec- essary . Thereupon he recommended to the Aqueduct Commissioners that this entire section of the embank- ment and core wall to the gatehouse be removed and the stone dam extended in its place . But while maintaining that the conditions allowed of no other conclusion , he recommended that a committee of three engineers be ap- pointed to pass upon a question of so vital and wide- spread importance . The Commissioners after personal investigation agreed in this and appointed a committee of expert engineers consisting of Messrs . J. J. R. Croes , Past President of the American Society of Civil Engineers ; Edwin F. Smith , Chief Engineer of the Schuvlkill Navigation Company and Elnathan Sweet , former Engineer of the State of New York . The committee after making an investiga- tion reported unanimously recommending this extension of the stone dam to the gatehouse . The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon .

The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon . On April 16 , 1902 , the Aqueduct Commissioners resolved to remove the em- bankment and core wall and to continue the main stone dam to the gatehouse . The estimated cost to complete the embankment and core wall under the original plan was $ 145,233.00 , while the preliminary estimate of the cost to remove the em- bankment and core wall and extend the main stone dam is $ 635,700 . The difference $ 490,467 being due to this modification , yet there will be a further increase because of the condition of the natural foundation of the core wall , as hereinafter described . In considering this esti- mate one should not loose sight of the fact that there has been a loss sustained of about $ 80,000 , the cost of that part of the core wall that had to be thus abandoned . In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge .

In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge . The hardest of this stone was full of eroded , open and mud - filled seams , the existence of mud being evidence that these seams had acted as passageways for water . Under date of April 1 , 1903 , Prof. Burr , who had con- curred in the condemnation of the wall , reported to Mayor Low as to the foundation as follows : " It is most fortunate that the core wall has been removed so as to dis- close the actual situation and thus remove what would have been a source of gravest danger to the completed embankment structure as originally planned . " Prof. J. E. Kemp , of Columbia University and Prof. J. J. Stevenson , of New York University , both geologists , were retained to investigate the locality affected . They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found .

They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found . The removal of this soft rock and the replacing it with masonry has again materially in- creased the cost of the structure . The work of building this masonry is now in progress . Another important change of plan is that of the gate- house , above referred to . This gatehouse is located in the embankment outside of the core wall . It is well up on the slope of the valley , its base being about 100 feet higher than the bed of the river . The substructure of this gatehouse is described as follows : It has four water chambers , 74 feet deep and about 12 feet square . Two on the southerly side of the structure are to control the flow of the water in the old Croton aqueduct which passes through this gatehouse . The other two on the northerly side , are to control the flow of water direct from the res- ervoir to the old aqueduct below the dam . These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base .

These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base . These walls which had been built to a height of fifty feet , would not have sufficient strength to resist the water pressure that would come against them , and their de- struction might result in a great losss of water from the reservoir and the demolition of the embankment , by the rush of water in falling a height of 150 feet to reach the valley below . On Dec. 18 , 1902 , on the writer's recom- mendation the Aqueduct Commissioners approved a plan providing for the reinforcement of these walls . The preliminary estimate of the cost to construct the dam under the original plan was $ 4,150,573 . This will be increased to about $ 6,400,000 . The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards .

The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards . The value of the work done to March 1 , 1904 is $ 5,363,000 . This most important of all structures to this great city , upon which its welfare would be almost wholly depend- ent , had to be mantled with all possible safeguards against its destruction . Thus the writer being brought face to face with the one paramount necessity that of the safety of this structure , was left no alternative but to modify the plan .

=== seq 12 ===

To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height . As an example , the Amawalk dam , which forms one of the upper Croton reservoirs , while only about half the height , 85 feet , yet has a base even wider than that of this embankment of unprecedented height .

This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height . As an example , the Amawalk dam , which forms one of the upper Croton reservoirs , while only about half the height , 85 feet , yet has a base even wider than that of this embankment of unprecedented height . And further , this embankment was hazardous because of the unsta- ble nature of its foundation . It was founded over a great refilled pit , which was 360 feet wide at the top , 170 feet at the base and 70 feet deep ; this pit was a necessary ex- cavation for the foundation of the end of the stone dam , which was 164 feet wide at the base as before stated . It would be impossible to refill this pit as compactly as orig- inal ground , hence the safety of the reservoir was de- pendent not only on an embankment of a problematic section , but this problematic section , rested upon an un- staple foundation . The second of the objections , the core wall of this embankment was 200 feet high and with no lateral pro- tection or support from original ground whatsoever , as the artificially placed earth on each side of the wall had the height of the wall itself , 200 feet . Considering the height of the wall , and this in artificially placed earth , it could be but an experimental structure , inasmuch as it woud be about twice the height of any heretofore built . The third objection , the double means afforded the water to reach the core wall , this is another serious ob- jection , as the water by starting at the end of the em- bankment in the reservoir and following between the face of the stone dam and the embankment would inevitably reach the core wall .

Considering the height of the wall , and this in artificially placed earth , it could be but an experimental structure , inasmuch as it woud be about twice the height of any heretofore built . The third objection , the double means afforded the water to reach the core wall , this is another serious ob- jection , as the water by starting at the end of the em- bankment in the reservoir and following between the face of the stone dam and the embankment would inevitably reach the core wall . It would be impossible to puddle or other- wise compact the embankment against the dam to pre- vent this , as settlement would surely follow in any em- bankment of this great height . This objectionable feature here exists because of the combination of a stone dam and an embankment , while it could not exist in either a continuous stone dam or , on the other hand , a continu- ous embankment and core wall . As to the second chan- nel by which the water could reach the wall there is also little doubt , for it would be afforded freer access through the refilled material of the great pit , than it would have STONE DAM البلد TOP OF 290 - FEET_ . CORE WALL MARCH 1ST 1901 EMOVED DISINTEGRATED FLIMESTONE SHATTERED LIME STONE THE NEW CROTON DAM LONGITUDINAL SECTION ON AXIS OF DAM , SHOWING CORE WALL REMOVED AND ITS DEFECTIVE LIME STONE FOUNDATION , WHICH HAS BEEN EXCAVATED FOR THE EXTENSION OF THE DAM . AK GATE HOUSE . CHAMBERS TO BE REMODELED AND REINFORCED in ordinary cases , where the wall below the original sur- face of the ground is in a narrow trench and protected by original soil . It would be useless to consider any proposi- tion to increase the width of the embankment , because the means afforded the water to reach the core wall along the face of the dam would always remain ; this is a most dan- gerous feature , as the core wall would not have sufficient weight or strength to resist the pressure of the water that would come against it .

CHAMBERS TO BE REMODELED AND REINFORCED in ordinary cases , where the wall below the original sur- face of the ground is in a narrow trench and protected by original soil . It would be useless to consider any proposi- tion to increase the width of the embankment , because the means afforded the water to reach the core wall along the face of the dam would always remain ; this is a most dan- gerous feature , as the core wall would not have sufficient weight or strength to resist the pressure of the water that would come against it . A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure . Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall . Such a structure can not be regarded as anything but an experiment . It is abnormal and unprecedented in all its dangerous features . The engineer might apply in vain to science for aid in computing the efficiency of such a structures ; he could get no light , for he could find not even the slightest guaranty of safety in a structure so built . The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish .

The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish . Thus , the writer , was thoroughly convinced that a change in the plan of the structure at this point was nec- essary . Thereupon he recommended to the Aqueduct Commissioners that this entire section of the embank- ment and core wall to the gatehouse be removed and the stone dam extended in its place . But while maintaining that the conditions allowed of no other conclusion , he recommended that a committee of three engineers be ap- pointed to pass upon a question of so vital and wide- spread importance . The Commissioners after personal investigation agreed in this and appointed a committee of expert engineers consisting of Messrs . J. J. R. Croes , Past President of the American Society of Civil Engineers ; Edwin F. Smith , Chief Engineer of the Schuvlkill Navigation Company and Elnathan Sweet , former Engineer of the State of New York . The committee after making an investiga- tion reported unanimously recommending this extension of the stone dam to the gatehouse . The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon .

The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon . On April 16 , 1902 , the Aqueduct Commissioners resolved to remove the em- bankment and core wall and to continue the main stone dam to the gatehouse . The estimated cost to complete the embankment and core wall under the original plan was $ 145,233.00 , while the preliminary estimate of the cost to remove the em- bankment and core wall and extend the main stone dam is $ 635,700 . The difference $ 490,467 being due to this modification , yet there will be a further increase because of the condition of the natural foundation of the core wall , as hereinafter described . In considering this esti- mate one should not loose sight of the fact that there has been a loss sustained of about $ 80,000 , the cost of that part of the core wall that had to be thus abandoned . In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge .

In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge . The hardest of this stone was full of eroded , open and mud - filled seams , the existence of mud being evidence that these seams had acted as passageways for water . Under date of April 1 , 1903 , Prof. Burr , who had con- curred in the condemnation of the wall , reported to Mayor Low as to the foundation as follows : " It is most fortunate that the core wall has been removed so as to dis- close the actual situation and thus remove what would have been a source of gravest danger to the completed embankment structure as originally planned . " Prof. J. E. Kemp , of Columbia University and Prof. J. J. Stevenson , of New York University , both geologists , were retained to investigate the locality affected . They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found .

They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found . The removal of this soft rock and the replacing it with masonry has again materially in- creased the cost of the structure . The work of building this masonry is now in progress . Another important change of plan is that of the gate- house , above referred to . This gatehouse is located in the embankment outside of the core wall . It is well up on the slope of the valley , its base being about 100 feet higher than the bed of the river . The substructure of this gatehouse is described as follows : It has four water chambers , 74 feet deep and about 12 feet square . Two on the southerly side of the structure are to control the flow of the water in the old Croton aqueduct which passes through this gatehouse . The other two on the northerly side , are to control the flow of water direct from the res- ervoir to the old aqueduct below the dam . These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base .

These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base . These walls which had been built to a height of fifty feet , would not have sufficient strength to resist the water pressure that would come against them , and their de- struction might result in a great losss of water from the reservoir and the demolition of the embankment , by the rush of water in falling a height of 150 feet to reach the valley below . On Dec. 18 , 1902 , on the writer's recom- mendation the Aqueduct Commissioners approved a plan providing for the reinforcement of these walls . The preliminary estimate of the cost to construct the dam under the original plan was $ 4,150,573 . This will be increased to about $ 6,400,000 . The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards .

The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards . The value of the work done to March 1 , 1904 is $ 5,363,000 . This most important of all structures to this great city , upon which its welfare would be almost wholly depend- ent , had to be mantled with all possible safeguards against its destruction . Thus the writer being brought face to face with the one paramount necessity that of the safety of this structure , was left no alternative but to modify the plan .

=== seq 13 ===

STONE DAM البلد TOP OF 290 - FEET_ . CORE WALL MARCH 1ST 1901 EMOVED DISINTEGRATED FLIMESTONE SHATTERED LIME STONE THE NEW CROTON DAM LONGITUDINAL SECTION ON AXIS OF DAM , SHOWING CORE WALL REMOVED AND ITS DEFECTIVE LIME STONE FOUNDATION , WHICH HAS BEEN EXCAVATED FOR THE EXTENSION OF THE DAM . AK GATE HOUSE . CHAMBERS TO BE REMODELED AND REINFORCED in ordinary cases , where the wall below the original sur- face of the ground is in a narrow trench and protected by original soil .

CORE WALL MARCH 1ST 1901 EMOVED DISINTEGRATED FLIMESTONE SHATTERED LIME STONE THE NEW CROTON DAM LONGITUDINAL SECTION ON AXIS OF DAM , SHOWING CORE WALL REMOVED AND ITS DEFECTIVE LIME STONE FOUNDATION , WHICH HAS BEEN EXCAVATED FOR THE EXTENSION OF THE DAM . AK GATE HOUSE . CHAMBERS TO BE REMODELED AND REINFORCED in ordinary cases , where the wall below the original sur- face of the ground is in a narrow trench and protected by original soil . It would be useless to consider any proposi- tion to increase the width of the embankment , because the means afforded the water to reach the core wall along the face of the dam would always remain ; this is a most dan- gerous feature , as the core wall would not have sufficient weight or strength to resist the pressure of the water that would come against it . A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure . Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall . Such a structure can not be regarded as anything but an experiment . It is abnormal and unprecedented in all its dangerous features . The engineer might apply in vain to science for aid in computing the efficiency of such a structures ; he could get no light , for he could find not even the slightest guaranty of safety in a structure so built .

Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall . Such a structure can not be regarded as anything but an experiment . It is abnormal and unprecedented in all its dangerous features . The engineer might apply in vain to science for aid in computing the efficiency of such a structures ; he could get no light , for he could find not even the slightest guaranty of safety in a structure so built . The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish . Thus , the writer , was thoroughly convinced that a change in the plan of the structure at this point was nec- essary . Thereupon he recommended to the Aqueduct Commissioners that this entire section of the embank- ment and core wall to the gatehouse be removed and the stone dam extended in its place . But while maintaining that the conditions allowed of no other conclusion , he recommended that a committee of three engineers be ap- pointed to pass upon a question of so vital and wide- spread importance .

Thus , the writer , was thoroughly convinced that a change in the plan of the structure at this point was nec- essary . Thereupon he recommended to the Aqueduct Commissioners that this entire section of the embank- ment and core wall to the gatehouse be removed and the stone dam extended in its place . But while maintaining that the conditions allowed of no other conclusion , he recommended that a committee of three engineers be ap- pointed to pass upon a question of so vital and wide- spread importance . The Commissioners after personal investigation agreed in this and appointed a committee of expert engineers consisting of Messrs . J. J. R. Croes , Past President of the American Society of Civil Engineers ; Edwin F. Smith , Chief Engineer of the Schuvlkill Navigation Company and Elnathan Sweet , former Engineer of the State of New York . The committee after making an investiga- tion reported unanimously recommending this extension of the stone dam to the gatehouse . The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon . On April 16 , 1902 , the Aqueduct Commissioners resolved to remove the em- bankment and core wall and to continue the main stone dam to the gatehouse . The estimated cost to complete the embankment and core wall under the original plan was $ 145,233.00 , while the preliminary estimate of the cost to remove the em- bankment and core wall and extend the main stone dam is $ 635,700 .

Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon . On April 16 , 1902 , the Aqueduct Commissioners resolved to remove the em- bankment and core wall and to continue the main stone dam to the gatehouse . The estimated cost to complete the embankment and core wall under the original plan was $ 145,233.00 , while the preliminary estimate of the cost to remove the em- bankment and core wall and extend the main stone dam is $ 635,700 . The difference $ 490,467 being due to this modification , yet there will be a further increase because of the condition of the natural foundation of the core wall , as hereinafter described . In considering this esti- mate one should not loose sight of the fact that there has been a loss sustained of about $ 80,000 , the cost of that part of the core wall that had to be thus abandoned . In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge . The hardest of this stone was full of eroded , open and mud - filled seams , the existence of mud being evidence that these seams had acted as passageways for water .

The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge . The hardest of this stone was full of eroded , open and mud - filled seams , the existence of mud being evidence that these seams had acted as passageways for water . Under date of April 1 , 1903 , Prof. Burr , who had con- curred in the condemnation of the wall , reported to Mayor Low as to the foundation as follows : " It is most fortunate that the core wall has been removed so as to dis- close the actual situation and thus remove what would have been a source of gravest danger to the completed embankment structure as originally planned . " Prof. J. E. Kemp , of Columbia University and Prof. J. J. Stevenson , of New York University , both geologists , were retained to investigate the locality affected . They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found . The removal of this soft rock and the replacing it with masonry has again materially in- creased the cost of the structure .

They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found . The removal of this soft rock and the replacing it with masonry has again materially in- creased the cost of the structure . The work of building this masonry is now in progress . Another important change of plan is that of the gate- house , above referred to . This gatehouse is located in the embankment outside of the core wall . It is well up on the slope of the valley , its base being about 100 feet higher than the bed of the river . The substructure of this gatehouse is described as follows : It has four water chambers , 74 feet deep and about 12 feet square . Two on the southerly side of the structure are to control the flow of the water in the old Croton aqueduct which passes through this gatehouse . The other two on the northerly side , are to control the flow of water direct from the res- ervoir to the old aqueduct below the dam . These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base .

These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base . These walls which had been built to a height of fifty feet , would not have sufficient strength to resist the water pressure that would come against them , and their de- struction might result in a great losss of water from the reservoir and the demolition of the embankment , by the rush of water in falling a height of 150 feet to reach the valley below . On Dec. 18 , 1902 , on the writer's recom- mendation the Aqueduct Commissioners approved a plan providing for the reinforcement of these walls . The preliminary estimate of the cost to construct the dam under the original plan was $ 4,150,573 . This will be increased to about $ 6,400,000 . The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards .

The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards . The value of the work done to March 1 , 1904 is $ 5,363,000 . This most important of all structures to this great city , upon which its welfare would be almost wholly depend- ent , had to be mantled with all possible safeguards against its destruction . Thus the writer being brought face to face with the one paramount necessity that of the safety of this structure , was left no alternative but to modify the plan .

=== seq 14 ===

in ordinary cases , where the wall below the original sur- face of the ground is in a narrow trench and protected by original soil . It would be useless to consider any proposi- tion to increase the width of the embankment , because the means afforded the water to reach the core wall along the face of the dam would always remain ; this is a most dan- gerous feature , as the core wall would not have sufficient weight or strength to resist the pressure of the water that would come against it .

in ordinary cases , where the wall below the original sur- face of the ground is in a narrow trench and protected by original soil . It would be useless to consider any proposi- tion to increase the width of the embankment , because the means afforded the water to reach the core wall along the face of the dam would always remain ; this is a most dan- gerous feature , as the core wall would not have sufficient weight or strength to resist the pressure of the water that would come against it . A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure . Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall . Such a structure can not be regarded as anything but an experiment . It is abnormal and unprecedented in all its dangerous features . The engineer might apply in vain to science for aid in computing the efficiency of such a structures ; he could get no light , for he could find not even the slightest guaranty of safety in a structure so built . The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish .

The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish . Thus , the writer , was thoroughly convinced that a change in the plan of the structure at this point was nec- essary . Thereupon he recommended to the Aqueduct Commissioners that this entire section of the embank- ment and core wall to the gatehouse be removed and the stone dam extended in its place . But while maintaining that the conditions allowed of no other conclusion , he recommended that a committee of three engineers be ap- pointed to pass upon a question of so vital and wide- spread importance . The Commissioners after personal investigation agreed in this and appointed a committee of expert engineers consisting of Messrs . J. J. R. Croes , Past President of the American Society of Civil Engineers ; Edwin F. Smith , Chief Engineer of the Schuvlkill Navigation Company and Elnathan Sweet , former Engineer of the State of New York . The committee after making an investiga- tion reported unanimously recommending this extension of the stone dam to the gatehouse . The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon .

The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon . On April 16 , 1902 , the Aqueduct Commissioners resolved to remove the em- bankment and core wall and to continue the main stone dam to the gatehouse . The estimated cost to complete the embankment and core wall under the original plan was $ 145,233.00 , while the preliminary estimate of the cost to remove the em- bankment and core wall and extend the main stone dam is $ 635,700 . The difference $ 490,467 being due to this modification , yet there will be a further increase because of the condition of the natural foundation of the core wall , as hereinafter described . In considering this esti- mate one should not loose sight of the fact that there has been a loss sustained of about $ 80,000 , the cost of that part of the core wall that had to be thus abandoned . In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge .

In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge . The hardest of this stone was full of eroded , open and mud - filled seams , the existence of mud being evidence that these seams had acted as passageways for water . Under date of April 1 , 1903 , Prof. Burr , who had con- curred in the condemnation of the wall , reported to Mayor Low as to the foundation as follows : " It is most fortunate that the core wall has been removed so as to dis- close the actual situation and thus remove what would have been a source of gravest danger to the completed embankment structure as originally planned . " Prof. J. E. Kemp , of Columbia University and Prof. J. J. Stevenson , of New York University , both geologists , were retained to investigate the locality affected . They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found .

They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found . The removal of this soft rock and the replacing it with masonry has again materially in- creased the cost of the structure . The work of building this masonry is now in progress . Another important change of plan is that of the gate- house , above referred to . This gatehouse is located in the embankment outside of the core wall . It is well up on the slope of the valley , its base being about 100 feet higher than the bed of the river . The substructure of this gatehouse is described as follows : It has four water chambers , 74 feet deep and about 12 feet square . Two on the southerly side of the structure are to control the flow of the water in the old Croton aqueduct which passes through this gatehouse . The other two on the northerly side , are to control the flow of water direct from the res- ervoir to the old aqueduct below the dam . These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base .

These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base . These walls which had been built to a height of fifty feet , would not have sufficient strength to resist the water pressure that would come against them , and their de- struction might result in a great losss of water from the reservoir and the demolition of the embankment , by the rush of water in falling a height of 150 feet to reach the valley below . On Dec. 18 , 1902 , on the writer's recom- mendation the Aqueduct Commissioners approved a plan providing for the reinforcement of these walls . The preliminary estimate of the cost to construct the dam under the original plan was $ 4,150,573 . This will be increased to about $ 6,400,000 . The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards .

The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards . The value of the work done to March 1 , 1904 is $ 5,363,000 . This most important of all structures to this great city , upon which its welfare would be almost wholly depend- ent , had to be mantled with all possible safeguards against its destruction . Thus the writer being brought face to face with the one paramount necessity that of the safety of this structure , was left no alternative but to modify the plan .

=== seq 15 ===

recommended that a committee of three engineers be ap- pointed to pass upon a question of so vital and wide- spread importance . The Commissioners after personal investigation agreed in this and appointed a committee of expert engineers consisting of Messrs . J. J. R. Croes , Past President of the American Society of Civil Engineers ; Edwin F. Smith , Chief Engineer of the Schuvlkill Navigation Company and Elnathan Sweet , former Engineer of the State of New York . The committee after making an investiga- tion reported unanimously recommending this extension of the stone dam to the gatehouse .

The Commissioners after personal investigation agreed in this and appointed a committee of expert engineers consisting of Messrs . J. J. R. Croes , Past President of the American Society of Civil Engineers ; Edwin F. Smith , Chief Engineer of the Schuvlkill Navigation Company and Elnathan Sweet , former Engineer of the State of New York . The committee after making an investiga- tion reported unanimously recommending this extension of the stone dam to the gatehouse . The general public will no doubt feel that great weight has been added to these conclusions by the concurrence of the eminent Engineers Prof. William H. Burr , occu- pying the Chair of Engineering of Columbia University , and Mr. Nelson P. Lewis , Chief Engineer of the Board of Estimate and Apportionment of the City of New York ; both of whom had been asked by Mayor Low to investigate and report thereon . On April 16 , 1902 , the Aqueduct Commissioners resolved to remove the em- bankment and core wall and to continue the main stone dam to the gatehouse . The estimated cost to complete the embankment and core wall under the original plan was $ 145,233.00 , while the preliminary estimate of the cost to remove the em- bankment and core wall and extend the main stone dam is $ 635,700 . The difference $ 490,467 being due to this modification , yet there will be a further increase because of the condition of the natural foundation of the core wall , as hereinafter described . In considering this esti- mate one should not loose sight of the fact that there has been a loss sustained of about $ 80,000 , the cost of that part of the core wall that had to be thus abandoned .

The difference $ 490,467 being due to this modification , yet there will be a further increase because of the condition of the natural foundation of the core wall , as hereinafter described . In considering this esti- mate one should not loose sight of the fact that there has been a loss sustained of about $ 80,000 , the cost of that part of the core wall that had to be thus abandoned . In March , 1903 , the core wall having been removed , it became apparent that the embankment and core wall would have been undermined and destroyed if completed under the original plan . The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge . The hardest of this stone was full of eroded , open and mud - filled seams , the existence of mud being evidence that these seams had acted as passageways for water . Under date of April 1 , 1903 , Prof. Burr , who had con- curred in the condemnation of the wall , reported to Mayor Low as to the foundation as follows : " It is most fortunate that the core wall has been removed so as to dis- close the actual situation and thus remove what would have been a source of gravest danger to the completed embankment structure as originally planned . " Prof. J. E. Kemp , of Columbia University and Prof.

Burr , who had con- curred in the condemnation of the wall , reported to Mayor Low as to the foundation as follows : " It is most fortunate that the core wall has been removed so as to dis- close the actual situation and thus remove what would have been a source of gravest danger to the completed embankment structure as originally planned . " Prof. J. E. Kemp , of Columbia University and Prof. J. J. Stevenson , of New York University , both geologists , were retained to investigate the locality affected . They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found . The removal of this soft rock and the replacing it with masonry has again materially in- creased the cost of the structure . The work of building this masonry is now in progress . Another important change of plan is that of the gate- house , above referred to . This gatehouse is located in the embankment outside of the core wall . It is well up on the slope of the valley , its base being about 100 feet higher than the bed of the river . The substructure of this gatehouse is described as follows : It has four water chambers , 74 feet deep and about 12 feet square . Two on the southerly side of the structure are to control the flow of the water in the old Croton aqueduct which passes through this gatehouse .

It is well up on the slope of the valley , its base being about 100 feet higher than the bed of the river . The substructure of this gatehouse is described as follows : It has four water chambers , 74 feet deep and about 12 feet square . Two on the southerly side of the structure are to control the flow of the water in the old Croton aqueduct which passes through this gatehouse . The other two on the northerly side , are to control the flow of water direct from the res- ervoir to the old aqueduct below the dam . These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base . These walls which had been built to a height of fifty feet , would not have sufficient strength to resist the water pressure that would come against them , and their de- struction might result in a great losss of water from the reservoir and the demolition of the embankment , by the rush of water in falling a height of 150 feet to reach the valley below . On Dec. 18 , 1902 , on the writer's recom- mendation the Aqueduct Commissioners approved a plan providing for the reinforcement of these walls . The preliminary estimate of the cost to construct the dam under the original plan was $ 4,150,573 . This will be increased to about $ 6,400,000 .

These walls which had been built to a height of fifty feet , would not have sufficient strength to resist the water pressure that would come against them , and their de- struction might result in a great losss of water from the reservoir and the demolition of the embankment , by the rush of water in falling a height of 150 feet to reach the valley below . On Dec. 18 , 1902 , on the writer's recom- mendation the Aqueduct Commissioners approved a plan providing for the reinforcement of these walls . The preliminary estimate of the cost to construct the dam under the original plan was $ 4,150,573 . This will be increased to about $ 6,400,000 . The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards . The value of the work done to March 1 , 1904 is $ 5,363,000 . This most important of all structures to this great city , upon which its welfare would be almost wholly depend- ent , had to be mantled with all possible safeguards against its destruction . Thus the writer being brought face to face with the one paramount necessity that of the safety of this structure , was left no alternative but to modify the plan .

The value of the work done to March 1 , 1904 is $ 5,363,000 . This most important of all structures to this great city , upon which its welfare would be almost wholly depend- ent , had to be mantled with all possible safeguards against its destruction . Thus the writer being brought face to face with the one paramount necessity that of the safety of this structure , was left no alternative but to modify the plan .

=== seq 16 ===

The hardest of this stone was full of eroded , open and mud - filled seams , the existence of mud being evidence that these seams had acted as passageways for water . Under date of April 1 , 1903 , Prof. Burr , who had con- curred in the condemnation of the wall , reported to Mayor Low as to the foundation as follows : " It is most fortunate that the core wall has been removed so as to dis- close the actual situation and thus remove what would have been a source of gravest danger to the completed embankment structure as originally planned . " Prof. J. E. Kemp , of Columbia University and Prof. J. J. Stevenson , of New York University , both geologists , were retained to investigate the locality affected . They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found .

They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found . The removal of this soft rock and the replacing it with masonry has again materially in- creased the cost of the structure . The work of building this masonry is now in progress . Another important change of plan is that of the gate- house , above referred to . This gatehouse is located in the embankment outside of the core wall . It is well up on the slope of the valley , its base being about 100 feet higher than the bed of the river . The substructure of this gatehouse is described as follows : It has four water chambers , 74 feet deep and about 12 feet square . Two on the southerly side of the structure are to control the flow of the water in the old Croton aqueduct which passes through this gatehouse . The other two on the northerly side , are to control the flow of water direct from the res- ervoir to the old aqueduct below the dam . These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base .

These two chambers are connected with the reservoir by three brick inlets , 10 feet in diameter . And thy are to hold water to a depth of 54 feet , yet the outer walls ( which are en- closed in an artificial embankment ) have a uniform thick- ness , from the base to top of but eight feet , while safe construction demands that they should be about four times that thickness at the base . These walls which had been built to a height of fifty feet , would not have sufficient strength to resist the water pressure that would come against them , and their de- struction might result in a great losss of water from the reservoir and the demolition of the embankment , by the rush of water in falling a height of 150 feet to reach the valley below . On Dec. 18 , 1902 , on the writer's recom- mendation the Aqueduct Commissioners approved a plan providing for the reinforcement of these walls . The preliminary estimate of the cost to construct the dam under the original plan was $ 4,150,573 . This will be increased to about $ 6,400,000 . The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards .

The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards . The value of the work done to March 1 , 1904 is $ 5,363,000 . This most important of all structures to this great city , upon which its welfare would be almost wholly depend- ent , had to be mantled with all possible safeguards against its destruction . Thus the writer being brought face to face with the one paramount necessity that of the safety of this structure , was left no alternative but to modify the plan . Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif .

=== seq 17 ===

feet , would not have sufficient strength to resist the water pressure that would come against them , and their de- struction might result in a great losss of water from the reservoir and the demolition of the embankment , by the rush of water in falling a height of 150 feet to reach the valley below . On Dec. 18 , 1902 , on the writer's recom- mendation the Aqueduct Commissioners approved a plan providing for the reinforcement of these walls .

feet , would not have sufficient strength to resist the water pressure that would come against them , and their de- struction might result in a great losss of water from the reservoir and the demolition of the embankment , by the rush of water in falling a height of 150 feet to reach the valley below . On Dec. 18 , 1902 , on the writer's recom- mendation the Aqueduct Commissioners approved a plan providing for the reinforcement of these walls . The preliminary estimate of the cost to construct the dam under the original plan was $ 4,150,573 . This will be increased to about $ 6,400,000 . The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards . The value of the work done to March 1 , 1904 is $ 5,363,000 . This most important of all structures to this great city , upon which its welfare would be almost wholly depend- ent , had to be mantled with all possible safeguards against its destruction . Thus the writer being brought face to face with the one paramount necessity that of the safety of this structure , was left no alternative but to modify the plan .

The value of the work done to March 1 , 1904 is $ 5,363,000 . This most important of all structures to this great city , upon which its welfare would be almost wholly depend- ent , had to be mantled with all possible safeguards against its destruction . Thus the writer being brought face to face with the one paramount necessity that of the safety of this structure , was left no alternative but to modify the plan . Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif .

=== seq 18 ===

Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif .

=== seq 19 ===

Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif .

=== seq 20 ===

Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif .

=== seq 21 ===

Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif .

=== seq 22 ===

Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif .

=== seq 23 ===

Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif .

=== seq 24 ===

Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif .

=== seq 25 ===

Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif .

=== seq 21 === Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif . === seq 22 === Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif . === seq 23 === Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif . === seq 24 === Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif . === seq 25 === Gaylord GAYLAMOUNT PAMPHLET BINDER Syracuse , N.Y. Stockton , Calif .