WSP04560

• File Number: 8271.300
• Description: Colorado River Basin Salinity Control Program - General Information and Publications - Reports
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 2/9/1994
• Author: John Hedlund
• Title: Salt Primer - Water and Salt Budgets
• Water Supply Pro - Doc Type: Report/Study

6

To develop implementation plans for the Colorado River Basin
salinity Control Program detailed hydrosalinity budgets have been
prepared for the basin, each unit, and for subareas selected for
planning. Each unit has characteristics unique to that unit.
salinity concentration in the river system has been monitored
for over 50 years(Irons,1965 & USOI,1991). The Colorado River
picks up about 9 million tons of salt as it flows 1400 miles from
the snow-covered peaks in the Colorado and Wyoming Rockies to
Mexico. About 47 percent of the salt load comes from natural
sources(EPA,1971) and is added to the 15 million acre-feet of
runoff in Arizona, California, Nevada, New Mexico, Colorado,
Utah, and Wyoming. Average salinity concentration or total
dissolved solids (TOS) in the headwaters is less than 50
milligrams per liter (mg/L) or parts per million (ppm). Salinity
at Imperial Dam, Arizona, the last major u.s. diversion point
before the water reaches Mexico, averages 870 mg/L. Without
salinity control measures the concentration is expected to rise
to over 1000 mg/L. Fluctuations of several 100 mg/l may occur
from year---to year, month to month, and daily due to natural
variations in climatic conditions which are beyond man's control.

The natural salinity concentration of the Colorado River has been
changed in two ways, by the addition of salt and the depletion of
water. Canal, lateral, and ditch seepage and deep percolating
irrigation return flows pick up an estimated 3.4 million tons of
salt per year from saline aquifers underlying irrigated cropland.
Salt contributions from irrigation return flow account for about
37 percent of the total salt load in the Colorado River according
to salinity studies over the last 35 years. Municipal and
industrial waste discharges account for about 1%, while basin
export accounts for another 3%, and evaporation from reservoirs
accounts for 12% (EPA,1971 & USBR, 1991). Irrigation also
accounts for about 50 percent of the depletion in the river and
concentrates salts in the diminished flow.

Irrigation activities have increased salinity of the Colorado
River substantially. In 1905, with 900,000 acres under
irrigation.in the basin, the flow weighted salinity concentration
of salt was 700 mg/L at Yuma, Arizona (USBR,1972). By 1968,
with 3 million acres irrigated, the weighted annual salinity
concentration was 850 mg/L. One of the most significant changes
in salinity concentration is due to regulation of natural flow of
the river. The storage in Lake Powell reduces the month to month
variation from the mean salinity below Glen Canyon Dam from 300
mg/l to 70 mg/l.

IRRIGATION WATER AND SALT BUDGETS

The difference in quantity and quality of irrigation water
applied and of subsurface return flow determines the salt load
pickup. Annual precipitation on irrigated cropland in the West
is usually from one to 10 inches and very little if any of this