gravity drains, was approximately $5.20 per acre; and the total cost 
of labor, material, and power during the 12 months preceding Sep- 
tember 30, 1923, was 29 cents per acre. 
Although the peculiar conditions of the Salt River Valley project 
were especially favorable to the operation, it is believed that a study 
of the results obtained in conjunction with the existing conditions 
will be valuable to those who may be confronted with problems simi- 
lar to those successfully dealt with on this project. 
THE NEED FOR DRAINAGE AND ADVANTAGES OF DRAINAGE 
BY PUMPING 
The Salt Eiver project, comprising about 203,000 acres of im- 
proved farm land, is located in south-central Arizona. With the 
exception of several abrupt, rocky protrusions, the Salt River Valley 
is a plain sloping gently toward the river. Salt River, which trav- 
erses the project for about 40 miles, and Agua Fria River, which 
flows along the western boundary, are in channels well below the 
general land surface and provide drainage outlets for all surface 
run-off. 
The soils consist chiefly of sandy clay loam and loess underlaid by 
strata of clay and caliche (lime accumulations, either of soft char- 
acter or firmly cemented)" which vary from a thin layer to a thickness 
of 100 feet or more. In places these strata are underlaid by extensive 
deposits of gravel and bowlders (figs. 4, 5, 6, 7, 9, and 10). The top 
soil absorbs water at a moderately slow rate and holds it well. From 
two to four hours are usually required for a 6-inch application of 
water to disappear from the surface, and in low spots water may 
stand for several days before finally evaporating or sinking. 
With the extension of irrigation, natural drainage outlets became 
overtaxed and the level of the water in the soil began to rise. Ac- 
cording to yearly observations made by the United States Reclama- 
tion Service during 1913-1917, the water levels of 97 wells distributed 
through the valley showed an average annual rise of about 1.4 feet, 
and the area in which the water level was within 10 feet of the 
surface increased from 13,000 to 64,000 acres, and a portion of this 
area had become damaged by alkali. 
Because of the relatively slow rate at which water can be drained 
from much of the soil of the valley and the thickness and depth 
below the surface of the water-bearing strata, drainage ditches of 
the usual depth have been only partially effective in ridding the 
surface soil of excess water. On the other hand, because of the great 
extent of coarse, water-bearing formation from which water may be 
recovered in large quantities by pumping, the low cost of electric 
power and the value of the recovered water for irrigation, the drain- 
age of the water-logged areas by pumping from wells has proved 
feasible and profitable. This plan was adopted in 1918 by the Salt 
River Valley Water Users' Association, which operates the project, 
and at the close of the 1923 irrigation season 99 pumps were in oper- 
ation. As a direct result, the area under which the water table was 
10 feet or less from the surface, was reduced from 64,200 acres in 
1918 to 17,662 acres in 1923. In practically all of the water-logged 
areas the ground water had been lowered sufficiently to permit of 
