STORAGE AND DISTRIBUTION. 



123 



the down-stream slope. The hearting may be of 

 concrete or random rubble, but the crest and the 

 apron, down which the water will flow, must be con- 

 structed of solid block in course masonry, and the 



H.W.L 



Jfamrner Dressed, McLSorvry 

 .3-7 (or more) 

 Concrete 



<- JC v 



FIG. 87. 



form is shown in fig. 87 Sluices should be provided 

 to let off flood water. 



It will often be found economical to make masonry 

 dams thinner than has been described, providing 

 for the thrust by means of 

 buttresses, the inner face 

 having a batter as well as 

 the outer one. 



The first thing to do is to //. 

 settle the amount of batter 

 to be given to the outer 

 face. 



Take, for instance, fig. 88. 

 The value of x is required. 

 Let T, /, T lf H and x be as 

 shown, while let the ratio of the clear space between 

 the buttresses to the thickness of those buttresses be 

 denoted by r. 



Then a general formula to find x will stand 



x ~ ly + r/ 2 \2(r- i) + / ' ' ^ 34 ^ 

 S being the specific gravity of the masonry usually 



