IMPKOVEMENT OF THE SOIL 49 



a system of gates so that the water can be run to or 

 cut off from any part of the lands at pleasure. The 

 length of the main canal and the cost of canal and 

 ditches will, of course, depend on the topography of 

 the region and on the character of the soil. Some soils 

 dig easily and yet hold water in the ditches well. Here 

 construction is cheap and easy. In rough broken 

 countries it is often necessary to carry the canals or 

 ditches over ravines or rocky places in flumes built 

 of lumber. In other regions there are places where 

 much of the water sinks into the ground and is lost. 

 Here it is necessary to line the ditches with clay or 

 sometimes even with cement. All this adds to the 

 cost of construction. 



Where no running streams are available, it is often 

 possible to provide water for irrigation by building 

 large dams across ravines in such a way as to make 

 reservoirs for catching and holding the water from 

 occasional rainstorms. The rain that falls in dry 

 countries usually comes in the form of heavy showers, 

 so that most of it runs off quickly from the hard, 

 baked ground, forming temporary floods in the ravines 

 and dry water courses. The catching and impound- 

 ing of this storm water is more expensive than 

 utilizing a running stream, but there are vast areas 

 that can be irrigated in no other way, and there is no 

 question but with the increase in value of agricultural 

 lands more and more of these irrigation reservoirs 

 will be built. In the case of running streams the 

 building of storage reservoirs for holding the waste 

 water largely increases the capacity of the stream 

 for irrigation. Water from reservoirs is distributed 



