144 IRRIGATION. 



which the water flows over the intermediate slopes. The 

 canals in this system follow a perfectly level course, and 

 much care is to be exercised to follow the sinuous course of 

 this level across the meadow. A very safe method is to 

 make the lower side of the canal of plank or slips of 

 board, over the edge of which the water will flow without 

 injury to the canal. The cost of this system of irriga- 



Fig.TL CATCH-WATEB FUBBOWS. 



tion is frequently not more than $10 per acre. The 

 canals need to be but very small ; a furrow that will ar- 

 rest the flow of water is all that is required, its main 

 office being to restrain the velocity of the water, and to 

 collect it from the numerous streamlets into which it soon 

 gathers, and again spread it in a thin sheet over the 

 whole surface. 



Where the surface admits of it, a series of slopes and 

 terraces may be made, which can be irrigated upon this 

 system. See fig. 72. In this case, the slopes may be 

 covered with grass, and the intervals cultivated if desired. 



Fig. 72. SLOPES AND TERBACES. 



The water which flows down the slope is caught in the 

 furrow at the foot, and then passes over the terrace on to 

 the next slope. The furrow at the edge of the terrace is 

 needed to retain the water sufficiently to thoroughly irri- 

 gate the soil of the terrace, which would possibly other- 

 wise receive less than its share. In this system of irriga- 

 tion, when the soil is open and porous and the supply of 

 water limited, it will be necessary to puddle the bottom 



