WSP00631

• File Number: 8272.900.30
• Description: Colorado River Basin Salinity Control Program - Indian Tribes
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 7/1/1993
• Title: Salinity Verification - Phase I Final Report for Navajo Nation Unit - San Juan county NM - Salinity Control Study
• Water Supply Pro - Doc Type: Report/Study

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DISCUSSION

According to USDI Progress Report No. 15, Qualiey of Waeer, Colorado River Basin,

the Colorado River normally carries about 9 million tons of salt past Hoover Dam

in 10 million acre-feet.of water each year. Of this amount, about l.million tons

of salt and 2 million acre-feet of water come from the San Juan River. The

Colorado River carries nearly twice the concentration of salt per acre-foot as is

carried by the San Juan River.

Salt loading or salt pick up is the difference between salt in the diverted water

and salt in surface and subsurface return flow. It is assumed that salt in the

water consumed by crops is leached by deep percolation. The estimated salinity

of the water returned to the river from the study area is greater than the 0.45

tOn per acre-foot ambient salinity of the water diverted for irrigation. Off-

farm canal seepage, onfarm ditch seepage, and deep percolating irrigation water

are estimated to pick up about 1.65 tons of salt per acre-foot of return.

Seepage from 302 miles of earthen canals and laterals is responsible for

returning an annual average of about 48 tons of salt load to the river per mile

of canal and lateral.

Extrapolating the
canal seepage
from ditch seepa
5.8 T/A for a total

the off-farm return from
T/A. Onfarm returns
an average of

up to the irrigated

o contribute an

nd deep percolation

salt pick up of 8.3 to

acre.

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