Section 319
NONPOINT SOORGE PROGRAM SOGGESS STORY
Improving Irrigation Efficiency and
Land Management Reduces Sediment Loads
Watprhnrlv Imnrnx/prl Excess sediment eliminated important streambed habitats
and threatened aquatic life in Wyoming's Rock Creek. As
a result, the Wyoming Department of Environmental Quality (WDEQ) placed Rock Creek
on Wyoming's 1996 Clean Water Act section 303(d) list of impaired waters. Landowners
implemented best management practices (BMPs) specifically designed to improve irrigation
efficiency. Project partners held an educational workshop aimed at improving landowners'
pasture and hay culture management in the watershed. These efforts successfully reduced
sediment loads, prompting WDEQ to remove Rock Creek from the state's 2004 303(d) list
of impaired waters.
Problem
Rock Creek originates in Wyoming's Bighorn
Mountains, along the northwestern boundary of the
Powder River Basin. The creek flows southeast for
approximately 15 miles before it joins Clear Creek
near the town of Buffalo. WDEQ classifies Rock
Creek as a type 2AB water, and thus it is protected
for drinking water, coldwater game and nongame
fisheries, fish consumption, aquatic life other than
fish, recreation, wildlife, industry, agriculture and
scenic value uses. Excess sediment caused physi-
cal degradation in 8 miles of Rock Creek, making
the creek unable to support its aquatic life desig-
nated use. Consequently, WDEQ added an 8-mile
segment of Rock Creek to the state's 1996 303(d)
list.
The Lake DeSmet Conservation District (LDCD)
conducted a planning and assessment project in
1997 to determine the source of the excess sedi-
ment. Their investigation suggested that the major
sources of sediment included a combination of
heavy cattle and horse grazing operations and inef-
ficient irrigation systems in the watershed.
Project Highlights
In 1999 the LDCD received section 319 project
funding to address these water quality issues as
part of a cooperative effort among the LDCD, U.S.
Figure 1. This is a post-project view of Rock Creek.
The sediment load has declined, and the creek once
again supports its aquatic life use.
Department of Agriculture (USDA) and private land-
owners. The project's primary goals and objectives
included implementing BMPs that improve irrigation
infrastructure and application methods. Landowners
improved irrigation efficiency by burying pipelines
and installing modern sprinkler systems. LDCD
supplemented these structural changes with a
2001 educational workshop that helped watershed
landowners find ways to improve pasture and hay
culture management practices.
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Results
The LDCD conducted BMP effectiveness monitor-
ing at several study sites between 1999 and 2001.
Data show that implementing BMPs improved
irrigation efficiency in the watershed from approxi-
mately 12 percent (pre-project) to 40 percent
(post-project). This monitoring also found that
application efficiency increased from approximately
18 percent to 41 percent and water conveyance
efficiency increased from approximately 46 percent
to 99 percent. In addition, water usage decreased
from approximately 19,978 acre-feet to 6,011 acre-
feet, which means that more water remains in the
creek channel to support aquatic life uses and less
excess pollutant-carrying irrigation water returns
to the stream. While these results clearly illustrate
a marked improvement in the irrigation efficiency
in the watershed, the corresponding effectiveness
monitoring data collected by LDCD were deter-
mined to be inconclusive because the data were
collected during the term of the project and not
after installing all structural improvements.
Total suspended solids (TSS) data in pre-project
irrigation return flow show wide seasonal and
discharge-related variability. However, concentra-
tions for irrigation return flows into Rock Creek and
similar adjacent watersheds typically exhibit mean
TSS values near 15 milligrams per liter (mg/L). An
annual irrigation efficiency-induced reduction of
13,967 acre-feet of return flows with a mean TSS
concentration of 15 mg/L would equal an annual
reduction of almost 285 tons of sediment kept out
of the creek.
The inability to draw immediate conclusions from
the LDCD report prompted WDEQ to reevaluate
the stream in 2003. This post-project effectiveness
monitoring found the substrate in Rock Creek to be
relatively free of sediment (Figure 1) with its ability
to support aquatic life uncompromised. Therefore,
WDEQ determined that Rock Creek fully supports
its aquatic life uses and, thus, removed it from
Wyoming's 2004 303(d) list.
Partners and Funding
The section 319 program contributed a total of
$178,743 in federal funds to this project, which was
awarded to LDCD to address these water quality
issues as part of a cooperative effort among the
LDCD, USDA and private landowners. In addition,
the partners conducted a section 319 planning
and assessment project and held an educational
workshop for landowners to educate them on
BMPs. Partners contributed a total of $85,687 in
nonfederal match.
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-08-001CC
September 2008
For additional information contact:
Jack Smith
Wyoming Department of Environmental Quality
307-673-9337 • jsmith@wyo.gov
Nikki Lohse
Lake DeSmet Conservation District
307-684-2526 • nikki.lohse@wy.nacdnet.net
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