DAMS 



83 



filled with smaller stones and cement mortar, forming a very 

 strong structure. 



In most low- and medium-head developments where large flood 

 discharges must be passed, the entire dam or a large part of it 

 must be built in the form of a spillway. It is important that its 

 size be sufficient to take care of the largest known floods, and in 



Cut-off Trench to be 

 determined in Held 



Note:-In calculating pressure* 



Concrete assumed to weight 

 110 Ibs. cu. ft. 



Silt assumed to weigh 115 Ibs. 

 per cu. ft 



overturning 2.5' 



Drains under toe of Dam to be 



determined by Engineer in Field 



Scale of Feet 



10 



15 



FIG. 37. Cross-section of Masonry Gravity Dam Shown in Fig. 36. 



order to be on the safe side it is in many instances designed for 

 10 to 15 per cent greater discharge capacity than any previous 

 record would show to have taken place. The downstream face 

 should be curved so that the water will follow the surface and 

 prevent vacuum from forming, and also so that it is discharged in a 

 horizontal direction, protecting the bed of the stream against 



