84 BULLETIN 1026, U. S. DEPARTMENT OF AGRICULTUEE. 



applied is light enough to prevent an undue loss by deep percolation. 

 The head used should be governed by the conditions above and the 

 soil. Large heads should be used when possible, as they save both 

 time and water if handled properly. 



The run-off from the lower end of the field averages 6 per cent 

 of the amount applied. This is a very low average, but there are 

 many farms where much improvement could be made along this 

 line. 



The average number of irrigations applied on the fields under 

 investigation ranged from 1.21 for wheat to 3.79 for potatoes. 



The average head used by one irrigator ranged from a minimum 

 of 1.85 second- feet for sugar beets to a maximum of 2.59 second-feet 

 for alfalfa. 



The number of acres irrigated per day by one person ranged from 

 an average of 4.45 for barley to 6.78 for potatoes. Beans were in 

 an entirely different class with an average of 15.63 acres per day 

 per man. 



The average duty in acre-feet per acre, measured at the head of 

 the farm lateral, was- Alfalfa, 2.57; wheat, 1.04; oats, 1.35; barley, 

 1.19; sugar beets, 1.86; potatoes, 2.20; beans, 0.69. 



Reservoirs are by far the most important factor govering the good 

 use of water in the valley. By their use water is made available 

 when and only when needed. AVithout them an entirely different 

 type of development would have resulted in the valley. 



The large number of reservoirs was made possible by natural 

 basins which could be developed with a minimum of trouble and 

 expense. For thirteen of these reservoirs with an aggregate capac- 

 ity of 72,000 acre-feet the average cost of development was $6.75 

 per acre-foot of capacity. 



The majority of reservoir dams are low earth fills, and slopes 

 are protected against erosion by rock riprap or concrete pavements. 

 For these comparatively short slopes both types of protection have 

 given satisfaction. 



Gate wells are now placed in the dam at the top of the inner 

 slope. Locating them either at the upper or lower end of the 

 outlet was found to be unsatisfactory and at times dangerous. 



Outlet conduits are generally of stone or concrete and are often 

 in cuts through the rim of the natural basin forming the bottom of 

 the reservoir. 



The aggregate capacity of reservoirs with decreed rights from 

 the main river is now in excess of the normal available supply and 

 further new projects of that type are not feasible. Storage develop- 

 ment in the future should be along the line of flood-control reser- 

 voirs high up on the stream by which the flow of the stream below 

 could be made to conform to actual current irrigation requirements, 



