WSP03142

• File Number: 8276.100
• Description: Grand Valley Unit - Colorado River Basin Salinity Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1978
• Title: On-Farm System Improvements for the Grand Valley
• Water Supply Pro - Doc Type: Publication

BACKGROUND

The 100 square mile area known as
the Grand Valley in west-central
Colorado 1s the subject of a salinity
control study to reduce pollution of
the Colorado River. The Colorado
River carries a large load of salts and
suspended sediment. Irrigated land
in the Grand Valley and highly saline
80i1s in the upland watershed contrib-
ute about 600,000 to 700,000 tons of
salt annually to the Colorado River.
Most of these salts are thought to be
leached from the soil and the under-
lying Mancos shale by deep percolation
and seepage from irrigation systems.
Following the passage of PL 92-500,
the Federal Water Pollution Control Act
Amendments of 1972, the Environmental
Protection Agency issued a regulation
requiring the states of the Colorado
River Basin to adopt water quality
standards and a plan of implementation
for salinity control. The plan includes
prompt implementation of four salinity
control units authdrized by the
Colorado River Basin Salinity Control
Act. PL 93-320. The Grand Valley is
one of these four units. The Soil
Conservation Service of the U.S. Depart-
ment of Agriculture is a cooperating
agency by law.

PURPOSE OF STUDY

As its part of the salinity control
study, SCS has evaluated the present
condition of on-farm irrigation systems
and management practices and determined
what can be done to reduce salt in the
river. Our activities attempted to
answer these questions:

1. What is the magnitude of on-farm
irrigation improvement needs?

2. What are the total installation
costs and annual levels of funding
required to implement the program?

3. What will be the reduction in
salinity to the Colorado River?

.sALT BUDGET ANALYSIS

002962

Salt in the Colorado River 1s accumu-
lated through soil erosion, deep
percolation from field irrigation, and
seepage losses from ditches and canals.
Permeability and depth of soils are
major characteristics affecting the
~olume of water passing through the
8011 profile and carrying salt to the
river. The salt budget attributed to
on-farm irrigation for the present
condition in the Grand Valley and for
three possible levels of improved
irrigation water management are shown
in the table. Presently, 360.000 tons
of salt are delivered annually to the
river from on-farm irrigation. Erosion
and sediment contribute about 80,000
tons of salt to the River each year.
The third major factor, seepage from
off-farm canals and laterals. contributes
an estimated 350.000 tons of salt. It
should be noted that the Salt Desert
area. containing exposures of the Mancos
Shale formation. is estimated to contri-
bute nearly half of the soluable salts
produced by erosion 1n the Grand Valley.

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