DAMS 89 



New York City Building Law, tested as prescribed by the Amer- 

 ican Society of Civil Engineers, and must more than fill the voids 

 of sand and stone mixed in the proportions as used. The sand 

 and stone used for masonry must be sound and permanent, clean, 

 hard, and not easily sheared or split. 



" Outlets: All dams must be provided with approved outlets 

 of sufficient size, and so located as to completely allow the im- 

 pounded water to be released when desired or necessary, and 

 precautions must be made to prevent leakage along the outlets. 



" Ice Pressure: From Dec. 1 to March 15 no dam shall have 

 the water higher than two-thirds the height of the dam, unless 

 permission is granted by the Conservation Commission to keep 

 the water above at a higher level. Dams liable to be full during 

 the above period must be built strong enough to resist any possible 

 ice pressure in addition to the water pressure, and dams not so 

 designed must have an outlet at two-thirds the height of the dam. 



" Aprons: Spillways of all dams must be provided with aprons 

 or other provision on the downstream side to prevent the under- 

 mining of the dam by the falling waters. 



" Wooden Dams: Wooden dams may be used for temporary 

 purposes, or where the reach of the water impounded above the 

 dam is not over 300 feet or its depth more than 10 feet. The 

 timber of the dam must be removed at the end of five years, 

 unless express permission is granted by the Conservation Com- 

 mission for a longer period. 



" The crib work of wooden dams shall be built in pockets not 

 more than 8 feet square, well fastened together with at least 

 f-inch spikes or bolts, long enough to pass through three timbers, 

 and the pockets solidly packed with stone. The upetream face is 

 to be built at an angle of three horizontal to one vertical, covered 

 with plank, on which is to be laid a good layer of gravel. If the 

 foundation is rock, the bottom timbers must be anchored to the 

 rock. 



" Earth Dams: The upstream half of earth dams shall be 

 composed of gravelly earth with about 15 per cent of clay, with 

 no stones over 4 inches near the upstream face, or, if there be a 

 core, next to the core on the upstream side. The earth is to be 

 moist, not wet, well rolled in 12-inch layers slightly sloping down 

 to the middle of the dam. The downstream hah , or part below 

 the core, may be composed of coarser materials and stones. The 



