Section 319
NONPOINT SOURCE PROGRAM SUCCESS STORY
Best Management Practices Drastically Reduce Sediment and
Restore Water Quality in Las Vegas Wash
Watprhnrlv Imnrnvpd ~'~'ie Las Vegas Wash drains the 1,600-square-mile Las Vegas
1 " Valley, delivering stormwater, urban runoff, and highly treated
effluent to Lake Mead, the nation's largest manmade reservoir and the primary water sup-
ply for millions of people in Nevada, Arizona, and southern California. These sources caused
water quality impairments to the lower wash due to excess sediment and iron transported with
that sediment. In 2002, Nevada placed the lower reach of Las Vegas Wash on its 303(d) list
of impaired waters, with impairments to aquatic life propagation (excluding fish) due to total
suspended solids (TSS). Following the construction of erosion control structures, restoration of
wetland areas, and removal of invasive vegetation, average TSS concentrations declined signifi-
cantly. This allowed the state to remove the lower reach from its 303(d) list in 2004.
Problem
During the past 30 years, the Las Vegas area of
southern Nevada experienced dramatic popula-
tion increases. Indeed, the 1,600-square-mile
metropolitan Las Vegas Valley is one of the
fastest growing areas in the United States. The
valley drains into Las Vegas Wash, which car-
ries stormwater runoff and wastewater 12 miles
to Las Vegas Bay, an arm of Lake Mead.
Rising population and development rates have
increased the volume of water discharged into
the wash. An increase in impervious surfaces
allows more stormwater runoff to flow directly
into the wash rather than be absorbed by
the soil. In addition, the growing population
produces a high volume of wastewater that is
discharged into the wash. The increased water
flow, when added to an area already prone to
flash flooding, accelerated erosion in the wash,
destabilized the stream channel, significantly
degraded wetland areas, and contributed
excessive sediment to Las Vegas Bay.
For state water quality management purposes,
Nevada divides the wash downstream of the
city of Las Vegas into two reaches. The lower
reach, which extends 5.12 miles upstream from
Weirs are low dams designed to reduce streambed erosion by
flattening the slope of the channel and slowing flows. Many weirs
are constructed of confined rock riprap, providing a somewhat
natural look (top). Other structures are built with concrete,
resulting in a more engineered look (bottom). Weirs, wetland
restoration, and invasive vegetation removal helped reduce TSS
concentrations in lower Las Vegas Wash and led to its removal
from the Nevada 303(d) list in 2004.
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Las Vegas Bay, has a state TSS water quality
standard of 135 mg/L to protect aquatic life
propagation (excluding fish). For a waterbody
to be deemed in compliance with the standard,
it must not exceed the standard more than 10
percent of the time over 5 consecutive years.
Between 1997 and 2001, the lower reach failed
to meet the 5-year exceedence criterion, so the
Nevada Division of Environmental Protection
(NV DEP) placed the lower reach on the 2002
state 303(d) list for impairments to aquatic life
propagation (excluding fish) due to TSS.
Results
Project Highlights
When NV DEP first listed the lower reach in
2002, efforts were already underway to restore
the lower reach and protect the waterbody.
In 1998 the Las Vegas Wash Coordination
Committee (LVWCC) met to develop a practical,
comprehensive plan to rehabilitate and manage
the wash downstream of the city of Las Vegas.
The Las Vegas Wash Comprehensive Adaptive
Management Plan (CAMP) was approved and
adopted in January 2000.
The CAMP identified various activities needed
to improve water quality, such as installing
weirs and other erosion control structures,
creating and restoring wetlands, and controlling
noxious and invasive plant species. The CAMP
also called for an extensive revegetation effort
to stabilize soils and replace previously lost
riparian and wetland habitat.
LVWCC sponsored numerous planting events
that helped increase citizen awareness and
foster community support for the restoration
effort. Citizen volunteers removed trash from
the wash and planted wetland, riparian, and
upland plant species. They also removed inva-
sive vegetation such as tall whitetop, which has
narrow and easily broken roots that destabilize
the soil and allow increased bank erosion.
LVWCC initiated an extensive long-term moni-
toring program to provide baseline water qual-
ity data and measure the success of erosion
control and revegetation efforts.
As of June 2006, the project has involved
constructing nine weirs, stabilizing more than
21,000 linear feet of streambank, restoring 33
acres of wetlands, and removing 500,000 pounds
of trash and 680 acres of tall whitetop.
While project water quality benefits had begun
to be realized before 2002, the lower reach of the
wash did not meet the 5-year threshold criteria
for TSS and was therefore placed on the 2002
Nevada 303(d) list. Water quality improvements
continued, however, with average TSS concentra-
tions declining 50 percent since 2001. Analysis of
1999-2003 water quality data showed that TSS
concentrations exceeded the 135 mg/L standard
11 times out of 130 samples collected. This repre-
sented an 8.5 percent noncompliance rate, below
the maximum 10 percent allowable rate.
With TSS data showing compliance with water qual-
ity standards, Nevada removed the lower reach's
aquatic life propagation (excluding fish) impairment
from its 303(d) list in 2004. The NV DEP will contin-
ue to review monitoring data to confirm continued
compliance with water quality standards.
Partners and Funding
The cooperation of 28 members of the LVWCC,
representing local, state, and federal agencies,
local environmental groups, businesses, and
interested citizens, was essential in the creation
of a comprehensive management plan for the Las
Vegas Wash. Volunteers also played an important
role in the project, providing the needed labor
for wetland and riparian plantings and invasive
vegetation removal. The overall cost to implement
the CAMP is projected to be approximately
$127 million through 2013.
As of 2006, $33 million has been spent on CAMP
implementation. Approximately $600,000 of sec-
tion 319 funds was used to support construction
of erosion control structures, bank revegetation,
and public outreach efforts. Participating agen-
cies contributed $1.8 million during the
2005-2006 fiscal year.
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, U.S. Environmental Protection Agency
T> Off ice of Water
2 Washington, DC
EPA841-F-05-003G
July 2006
For additional information contact:
Keiba Crear
Southern Nevada Water Authority
Las Vegas Wash Coordination Team
702-822-3388
keiba.crear@snwa.com
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