9626

• UCREFRP Catalog Number: 9626
• Author: Butler, D. L.
• Title: Effects of Piping Irrigation Laterals on Selenium and Salt Loads, Montrose Arroyo Basin, Western Colorado.
• USFW Year: 2001.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

Effects of Piping Irrigation Laterals on Selenium
and Salt Loads, Montrose Arroyo Basin,
Western Colorado
By David L. Butler
Abstract
Selenium and salinity are water-quality
issues in the Upper Colorado River Basin. Certain
water bodies in the lower Gunnison River Basin,
including the lower Gunnison River and the
Uncompahgre River, exceed the State standard for
selenium of 5 micrograms per liter. Remediation
methods to reduce selenium and salt loading in
the lower Gunnison River Basin were examined.
A demonstration project in Montrose Arroyo,
located in the Uncompahgre River Basin near
Montrose, was done during 1998-2000 to deter-
mine the effects on selenium and salt loads in
Montrose Arroyo from replacing 8.5 miles of
open-ditch irrigation laterals with 7.5 miles of
pipe. The participants in the project were the
National Irrigation Water Quality Program, the
Colorado River Basin Salinity Control Program,
the Uncompahgre Valley Water Users Associa-
tion, and the U.S. Geological Survey.
The placing of five laterals in pipe signifi-
cantly decreased selenium loads in Montrose
Arroyo. The selenium load at the outflow moni-
toring site was about 194 pounds per year less
(28-percent decrease) in the period after the
laterals were placed in pipe. More than 90 percent
of the decrease in selenium load was attributed to
a decrease in ground-water load.
Salt loads also decreased because of the
lateral project, but by a smaller percentage than
the selenium loads. The salt load at the outflow
site on Montrose Arroyo was about 1,980 tons per
year less in the post-project period than in the pre-
project period.
All of the effects of the demonstration.
project on selenium and salt loads probably were
not measured by this study because some of the
lateral leakage that was eliminated had not neces-
sarily discharged to Montrose Arroyo upstream
from the monitoring sites. A greater decrease in
selenium loads relative to salt loads may have
been partially the result of decreases in selenium
concentrations in ground water in some areas.
INTRODUCTION
Salinity (or the dissolved-solids concentration)
is a concern in the Colorado River Basin in the United
States and Mexico because of its adverse effects on
agricultural, municipal, and industrial users (U.S.
Department of the Interior, 1999). The Salinity
Control Act of 1974 (Public Law 93-320) created the
Colorado River Basin Salinity Control Program to
investigate, plan, and construct projects to reduce salt
loading to the Colorado River. Some salinity-control
projects constructed by the Bureau of Reclamation
(BOR) include lining or replacing open canals and
laterals with pipe for the purpose of decreasing salt
loading caused by leakage from irrigation-distribution
systems. In the lower Gunnison River Basin, canal and
lateral leakage provides recharge to shallow ground
water. In areas containing soils and outcrops with high
salt content, such as the Mancos Shale on the east side
of the Uncompahgre Valley, considerable salt loading
occurs from canal and lateral leakage (Bureau of
INTRODUCTION