WATER 1 1 1 



by natural slopes of the valley, will usually be 

 satisfactory in outline. The dam will be the diffi- 

 cult part to manage. The site for this should be 

 chosen where the valley is narrow. Ample pro- 

 vision must be made in the overflow for the larg- 

 est freshet that can come. The water in falling 

 over the dam would gouge out any yielding material. 

 A durable cement apron must, therefore, be con- 

 structed with protection at the sides, and this must 

 be carried to a point where the flow of the stream 

 below the dam is comparatively level. It is well 

 to subordinate this cement apron by inserting 

 bowlders while the cement is soft and by making 

 use also of cobblestones, gravel and overhanging 

 bushes. If the overflow can be prolonged into a 

 series of falls and rapids with intervening pools, 

 it will add interest to the lake's outlet and aid in 

 producing a natural effect. No masonry or cement 

 work should rest on filled ground. If the overflow 

 is carried along the side of the valley instead of 

 the center for a short distance it may help in getting 

 a solid foundation, and in giving an interesting vari- 

 ation to the line of the channel. When the valley 

 in which the dam is constructed is broader than the 

 space required for the greatest overflow, a portion 



