66 IRRIGATION FARMING. 



high-water Hue as the point halfway down the bunk 

 therefrom will bound the given area, or the area ma}* be 

 bounded by the center line, either of the whole bank, or 

 of the top of the bank. These conditions do not of 

 course obtain where the natural sides of a ravine or canon 

 are to form the greater portion of the reservoir's contour. 

 Usually these considerations will not be of much impor- 

 tance, but in the case of joint ownership or of contracting 

 for the construction they may be important, and should 

 then be clearly understood and carefully specified. 



Construction. One of the first things to be done 

 after the site is secured is to make provision to draw off 

 the water. In building a large reservoir with an earth 

 embankment, wooden boxes or cribs of timber (although 

 sometimes employed) are not to be recommended for per- 

 manent use, as they soon decay, are very difficult to re- 

 place, are a source of weakness to the reservoir, and do 

 not admit of easily inserting a gate which can be freely 

 operated. Stone culverts laid in cement are more costly 

 and substantial as a rule, but require a special gate, which 

 may give trouble. Iron piping, of which there are sev- 

 eral kinds in the market, is perhaps the most suitable, 

 and by its use ono can purchase the standard low-pres- 

 sure water valves such as are in use in city waterworks, 

 that are guaranteed to give satisfaction. In laying the 

 pipe care must be taken to provide a safe and continuous 

 bearing beneath it, otherwise the load imposed by the 

 earth above will cause portions to settle and so loosen 

 the joints. 



It is necessary, too, to dig one or more cross trenches 

 from the pipe and pack them full of concrete, clay or 

 good earthen puddle, bringing the same up two or inr- 

 feet above the pipe so as to arrest any leakage along the 

 outlet pipe. The surface upon which embnnkmenf ~ 

 to rest should be plowed ;ind the roots of hiisho< :md 

 weeds removed to the outer toe of the slop , ul Ur which 



