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1 NONPOINT SOURCE SUCCESS STURY

Implementing Best Management Practices Improved Lake Ws
Waterbody Improved
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Lake Washington is a 2,965-acre oxbow lake formed by an
abandoned meander of the Mississippi River. Sediment inputs
from agricultural activities in the watershed contributed to an impairment of the lake for its
designated use of aquatic life use support. Lake Washington was placed on Mississippi's 1996 Clean
Water Act (CWA) section 303(d) list of impaired waters for being impaired by sedimentation. The
local soil and water conservation district (SWCD) worked with partners to implement a series of
erosion control best management practices (BMPs). Monitoring was conducted after the BMPs were
implemented, and Lake Washington was assessed as attaining its aquatic life designated use in the
2018 CWA section 305(b) report.
Problem
The Lake Washington watershed is in Washington
County near the Mississippi River in the Mississippi
Deita, an area of the state that is very flat and has
tittle, to no relief (Figure 1). Before 2014, the Lake
Washington watershed was delineated at a 27,861-
acre IHUC-10 scale due to the difficulty in defining flow
paths and watershed boundaries. Later use of light
detecting and ranging (LIDAR) remote sensing resulted
in the Identification of two HUC12. watersheds for Lake
Washington—North Lake Washington (15,805 acres)
and South Lake Washington (15,539 acres)—for a total
of 31,344 acres.
According to the 2016 National Land Cover Dataset
(NLCD), the combined land uses for the Lake
Washington watersheds include 69 percent cropland,
16 percent wetlands, 11 percent water and 3 percent
urban. The remaining 1 percent is made up of forest-
land, pastureland and scrub/barren land.
Lake Washington was monitored and assessed as not
attaining its designated use classification of aquatic life
support, which led to it being listed on Mississippi's
1996 CWA section 303(d) list of impaired waters.
Further study showed that the impairment was due to
sedimentation, and a Lake Washington Total Maximum
Daily Load (TMDL) was developed and approved by the
U.S Environmental Protection Agency (EPA) in 2003.
This TMDL stated that a 30 percent to 56 percent
reduction in the amount of sediment loading would be
needed for Lake Washington to attain its designated
use classification.
Lake Washington Subwatersheds
MWS 9442 MWS 9446
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MDEQ
Figure 1. Lake Washington is in western Mississippi.
Story Highlights
in 2007 the Washington County SWCD developed a
watershed plan. In 2008, the Mississippi Department
of Environmental Quality (MDEQ) partnered with the
Mississippi Soil and Water Conservation Commission
and the U.S. Department of Agriculture's Natural
Resources Conservation Service (NRCS) to implement

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BMPs within the Lake Washington watersheds
to address sedimentation. BMPs were imple-
mented between 2008 and 2011 and included
the installation of 139,712 feet of dikes, 153
grade stabilization structures, 13 water control
structures, and six rock outlet protection
features (Figure 2).
MDEQ partnered with the U.S. Geological Survey
(USGS) to conduct monitoring at a location
downstream of BMPs within the watershed. This
monitoring was intended to provide Information
on water quality at the edge of agricultural lands
before the water flows into intermittent and
perennial streams. The data were collected as
part of a special study designed to evaluate BMP
effectiveness on agricultural lands during storm
flow events. USGS conducted monitoring before
the implementation of the CWA section 319-
funded BMPs to establish a baseline for water
quality. Monitoring resumed after installation of
the BMPs, and data were collected to determine
if implementation of BMPs on the landscape had an
impact on water quality.
Results
MDEQ's ambient monitoring program for lakes
includes three monitoring locations on Lake
Washington, one each in the northern (111B51),
middle (570WSH01) and southern (111B52) parts
of the lake. Monitoring is generally conducted in a
manner that allows samples to be collected during the
critical period for lakes in Mississippi, which is during
the summer and fall (when temperatures are higher,
there is less rainfall, and periods of stress due to low
dissolved oxygen are more likely to occur). Data were
evaluated at each monitoring location individually
because they were determined to represent different
portions of the lake and different potential influences
to water quality as various landscape areas drain into
the lake and mix. Using the data, Lake Washington was
assessed as attaining its designated use classification
of aquatic life use support in Mississippi's 2018 and
2020 section 305(b) water quality assessment reports.
As part of this project, USGS collected monitoring
data before and after BMP implementation. Although
Figure 2. Four grade stabilization structures, including one
antivortex structure.
some data were collected at baseflow, most of the
sampling occurred during storm events. The results
from the data collection and analysis were published in
the Journal of Soil and Water Conservation: Assessing
water quality changes in agricultural drainages:
Examples from oxbow lake tributaries in northwestern
Mississippi, United States, and simulation-based power
analysis (Murphy, J.C.; Hicks, M.; & Stocks, S., 2020).
The edge of field data showed that there was a "...35%
or more decrease in event concentration [for more
than half of the constituent measured] following a
period of intense BMP implementation."
Partners and Funding
Because of a high level of stakeholder Interest, the
restoration project of Lake Washington was a collec-
tive effort between the Mississippi Soii and Water
Conservation Commission, MDEQ, EPA, NRCS, and
the Washington County SWCD. The total cost of the
overall project was $2,425,909, of which $820,025 was
comprised of CWA section 319 funds. Participating
stakeholders contributed a total of $1,605,884
towards the implementation of practices within this
watershed. Additionally, NRCS funded $980,814 of
practices within the larger HUC 10 that encompasses
both of the HUC 12.s that surround Lake Washington.
&
PROl*°
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U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA 841-F-20-001W
October 2020
For additional information contact:
Ajay Parshotam
Mississippi Department of Environmental Quality
601-961-4253 • aparshotam@mdeq.ms.gov
Patrick Vowell
Mississippi Department of Environmental Quality
601-961-5387 • pvowell@mdeq.ms.gov

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