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Section 319
NONPOINT SOURCE PROGRAM SUCCESS STORY
Nine Eagles Lake Overcomes Siltation and Turbidity Problems
WatPrbndv Imnrnvpd ^ven t'10u9'1 tne Nine Eagles Lake watershed lies within Nine
! " Eagles State Park and is almost entirely forested, erosion has
created siltation and turbidity problems in the lake. Sediment basins were constructed to
slow sediment delivery to the lake, and trails were reworked to reduce erosion. Post-proj-
ect monitoring data reveal an 85 percent reduction in sediment delivery, exceeding the 50
percent reduction goal set by the total maximum daily load (TMDL).
Problem
In 1998 Iowa included Nine Eagles Lake on
the state's 303(d) list due to high turbidity.
The main cause of turbidity in the lake is
colloidal clays, which remain suspended for
long periods. The Iowa Department of Natural
Resources (IDNR) completed a forestry
management plan for the state park area in
February 2001. A detailed assessment of the
area identified improperly maintained trails and
failing sediment ponds as two of the leading
causes of erosion.
Project Highlights
In 2001 EPA approved a TMDL for turbidity in
the Nine Eagles Lake watershed. The TMDL
established water clarity targets (as measured
by a Secchi disk depth) of 1.25 meters and a 50
percent reduction in sediment delivery.
To accomplish these goals, IDNR developed
an implementation plan for Nine Eagles Lake
focusing on reducing sediment delivery in the
watershed. Section 319 grant funds were used
to construct 17 sediment basins. In 2003 the
IDNR Parks Bureau rerouted and reworked some
of the trails to reduce impacts. Throughout the
project, care was taken to protect the forested
areas, home to the endangered Indiana bat.
Nine Eagles Lake is a popular recreation area where visitors enjoy
swimming, boating, and fishing.
Results
To evaluate the impact of the project, bathy-
metric mapping was used to map the original
lake bottom and the depth of sediment depos-
its. Further monitoring of Nine Eagles Lake
took place in 2000-2004 as part of the Iowa
Lakes Survey.
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