KESERVOIUS AXD PONDS. G5 



a very simple and easy task, especially where only 

 nil earth excavation is required, on flat land or in a 

 draw. If a place can be found from which the water 

 will naturally run in several directions, all the better, 

 because more land may then be reached at less cost. 

 Where there is a good clay subsoil, not porous, and the 

 soil above has in it considerable admixture of clay, a 

 first-class reservoir may be constructed out of the soil. 



In treating the construction of reservoirs we shall en- 

 deavor to take up the subjects separately, so that the 

 reader may not be confounded as to instructions that may 

 apply to a, work of lesser importance than that intended. 

 Large reservoirs are a menace too often to public safety 

 and mark the danger line in irrigating works, so that no 

 serious mistake should be made in building them. 



Laying Out Reservoirs. As we have said be- 

 fore, reservoirs should be built on as high ground as pos- 

 sible. Never select a place for a reservoir where the 

 bottom is more than four or five feet below the point of 

 delivery, for all surplus water below this point does no 

 good, and a dam must be built just so much stronger to 

 hold this extra head. The pressure on the dam is no 

 greater where the flowage is large than "where it is small. 

 It is the bight of the column of water at the darn that 

 must be figured on. High dams when not properly built 

 are unsafe. Surface is the one thing most desirable in 

 locating a reservoir. Get an idea of the size to be at- 

 tained before the work is begun, and at the same time 

 make a calculation as to the capacity of the proposed 

 basin when completed. 



The size having been determined the staking out 

 follows. If the reservoir is to cover a given area the 

 whole banks will be within the area, and the foot of the 

 outer slope will bound the given area. If the area is to 

 exclude the bank, the foot of the inner slope will bound 

 the area. If the water is to cover a given area, then the 

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