The dissolved-solids concentration in Colorado River water increases from less than 50 mg/L (milligrams per liter) at the river's origin to about 700 mg/L at the California border and to about 900 mg/L at the United States-Mexico boundary. Much of the latter increase is due to depletion by agricultural use and irrigation return water with salts leached from soils under cultivation.
Forty sites in three agricultural areas--Fort Mojave, Bard Valley, and Palo Verde Valley--were sampled to describe the dissolved-solids concentrations in return flows. Emphasis was on Palo Verde Valley.
In the Fort Mojave area, the dissolved-solids concentration of Colorado River water was about 700 mg/L, while the concentration in water at the tile-drain convergence averaged about 2,500 mg/L. In the closed sump that presently receives all irrigation return, concentrations ranged from 812 to 1,760 mg/L.
In Bard Valley, water diverted from the river had an annual mean dissolved-solids concentration of about 835 mg/L. During the study, concentrations in the two main drains carrying irrigation return water ranged from 953 to 1,290 mg/L.
Selected drains in Palo Verde Valley were sampled several times to determine dissolved-solids loads from subareas within the valley. Loads determined in this study were compared with those of an earlier study. In agreement with the earlier study, loads were found to be largest from three subareas in the southern half of the valley and comparatively small from the four subareas in the northern half. Smaller loads were found in this study from all subareas, however. The differences are thought to be due to generally lower water discharge observed in drains during this study.
