108 



IRRIGATION. 



This will be found a very convenient arrangement. 



Figures 44 and 45 are intended to represent a typical 



form of such a reservoir as this. The spring, escaping by 



a small stream, seen in the plan, fig. 45, occupies the 



Fig. 45. PLAN OF RESERVOIR. 



point a, in fig. 44. The ground around and below the 

 spring is excavated as shown by the dotted line, (fig. 45), 

 and by the part lightly shaded, marked c, in fig. 44. The 

 earth removed serves to make the dam which is construct- 



Fig. 46. TRAP FOR DISCHARGING RESERVOIR. 



ed in the manner hereafter described. (Page 111). A pipe 

 is laid in the dam, for convenience not far from the sur 

 face, and a valve, operated by a key, d, closes and opens 

 the pipe. The pipe is in fact a siphon, and if opened 



