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Section 319
NDNPDINT SOURCE PROGRAM SUCCESS STORY
Sediment Basins at Slip Bluff Lake Reduce Sediment by 85 Percent
WatPfbodv ImnrovPd Even tnou9n 7(-) Percent °f Slip Bluff Lake's 240-acre water-
shed lies within Slip Bluff Lake Park, erosion occurring
throughout the watershed created a sediment problem in the lake. Sediment control basins
were constructed throughout the watershed to slow sediment delivery, and the lake's shore-
line was stabilized with riprap. Sediment delivery was reduced by 64 percent, exceeding
the 50 percent goal set by the total maximum daily load (TMDL).
Problem
Iowa included Slip Bluff Lake on the state's
1998 303(d) list because of impairments due
to siltation. The main source of sediment
delivery to the lake was gully and streambank
erosion in the forested areas of the watershed.
This erosion contributed colloidal clays, which
stay in suspension for long periods. Shoreline
erosion was also contributing large amounts of
sediment to the lake.
Project Highlights
In August 2001 EPA approved a TMDL for
siltation that called for a 50 percent reduction
in sediment delivery to the lake. To accomplish
this goal, the Decatur County Conservation
Board and the Decatur Soil and Water Con-
servation District proposed the construction
of two large basins to slow sediment deliv-
ery originating from gully erosion. The Iowa
Department of Natural Resources' (IDNR)
Nonpoint Source Pollution Program provided
further suggestions to address the problem
using a watershed approach. As a result, the
plan was expanded to include seven smaller
sediment basins throughout the watershed. To
further stabilize the shoreline of Slip Bluff Lake,
the Iowa Department of Transportation and
the Iowa Department of Agriculture and Land
Stewardship, Division of Soil Conservation
(IDALS-DSC), provided funds to riprap portions
of the shoreline.
Sediment basins
prevent excess
sediment from
reaching the lake
by collecting
runoff water and
allowing sediment
to settle out of
the water and be
deposited in the
sediment basin.
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Slip Bluff Lake Watershed
Structure Locations
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V Ir -
Jr,. ^ ^
Sediment control structures were constructed throughout the watershed to reduce
sediment delivery to the lake.
To ensure the continued success of this
project, the Decatur County Conservation
Board maintained the project by planting
additional seedings in exposed soil on the
constructed sediment basins.
Results
Following the installation of the sediment
basins, sediment delivery to Slip Bluff Lake
was recalculated. Monitoring data indicate
a 64 percent reduction in sediment delivery,
exceeding the 50 percent goal set by the
TMDL. The sediment reduction also resulted
in a 50 percent improvement in water transpar-
ency. Slip Bluff Lake is no longer listed on the
Iowa 303(d) list for sediment.
Partners and Funding
IDALS-DSC Watershed Protection Program
Funds totaling $35,000 covered the cost of
constructing the two large sediment basins,
and IDNR, through section 319, provided
$31,219 for the construction of the seven
smaller sediment control structures. The
Decatur County Conservation Board provided
additional project funding, and IDALS-DSC and
the Iowa Department of Transportation provid-
ed funds for riprap of portions of the shoreline.
The IDNR Fisheries Bureau helped determine
the impact of the project by conducting an
aquatic life assessment at Slip Bluff Lake.
'. U.S. Environmental Protection Agency
\ Office of Water
a Washington, DC
EPA841-F-05-004E
July 2005
For additional information contact:
Richard Erke
Decatur County Conservation Board
641-446-7307
Kevin Reynold
Natural Resources Conservation Service
641-446-4135
Ubbo Agena
Iowa Department of Natural Resources
515-281-6402
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