\
Section 319
NDNPDINT SDURCF WXM SUCCESP STDRY
Innovative System Clears Up Sediment Problem in Nebraska Lake
WatPrhndv Imnrnvpd Valentine Mill Pond was a popular destination for fishing and
! " swimming from the turn of the century until the 1970s, when
sediment problems made it impossible to enjoy the lake as before. Mechanical dredging
deepened the lake and a sediment bypass system was designed and constructed to elimi-
nate future sediment buildup. The sediment bypass system has effectively addressed the
sedimentation problem, and the pond was removed from the state's 303(d) list in 2003.
Problem
Valentine Mill Pond was originally created in the
1890s by S.F. Gilman to power a gristmill. Since
the 1970s the lake had shrunk from more than
30 acres to less than 15 acres. Exposed mud
bars indicated the source of the problem—
excessive sediment. A diagnostic feasibility
study conducted by the Middle Niobrara
Natural Resources District (NRD) indicated that
the primary water quality concern was the
amount of sand being deposited in the pond.
Minnechaduza Creek, the pond's water source,
was depositing as much as 60 tons of sediment
into the lake daily. As a result of the feasibility
study, Valentine Mill Pond was added to the
Nebraska Department of Environmental
Quality's (DEQ) section 303(d) list for impair-
ment to aquatic life due to excessive sediment.
Project Highlights
Mechanical dredging was necessary to remove
sediment deposits and deepen the lake, but
that alone would not solve the excessive sedi-
mentation problems. To prevent excessive
sedimentation from reoccurring, an innovative
solution was needed. Rollin Hotchkiss, Ph.D.,
director of the Albrook Hydraulics Lab at
Washington State University, joined the project
team as a special consultant to Olsson Environ-
mental Services. Dr. Hotchkiss, formerly with
the University of Nebraska, had conducted
research involving sediment bypass systems.
To address the unique problems of Valentine
Pond, he designed a "hydrosuction
As part of the project, a unique labyrinth spillway
was constructed to pass large storm event flows
without manual operation. The hydrosuction system
passes around the dam shown here.
sediment removal system" with a unique
labyrinth spillway.
The system is designed to capture sediment as
it enters the pond and to transport it via a pipe-
line around the dam to be discharged back into
Minnechaduza Creek, without the use of exter-
nal energy. "The system was also designed
with the capability of collecting, through hydro-
suction dredging, the sediment that was not
captured by the bypass system," said Daryoush
Razavian of Olsson Environmental Services.
"We believe that the sediment removal system
implemented at the mill pond is the first system
operating in the world capable of both bypass-
ing and dredging sediment."
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Pre- and Post-Project Summer Conditions for Valentine Mill Pond
Conservation pool storage
Total phosphorus
Dissolved orthophosphorus
Total suspended solids
Water clarity
Algae density
Nitrate nitrogen
Number of
Samples
NA
13
14
14
9
10
14
Pre-Project Median
1997-1999a
76 acre-feet
0.13mg/L
0.05mg/L
31.0 mg/L
21 inches
5.38 mg/m3
0.45 mg/L
Number of
Samples
NA
4
5
5
5
4
5
Post-Project Median
2003a
162 acre-feet
0.07 mg/L
0.02 mg/L
6.5 mg/L
57 inches
7.51 mg/m3
0.21 mg/L
% Change
+ 113%
-46%
-60%
-79%
+ 170%
+ 40%
-54%
'Median not applicable to pool storage.
Results
The sediment removal system has effectively
addressed the problem of excess sedimenta-
tion in Valentine Mill Pond. Ongoing monitoring,
conducted by the Nebraska DEQ, has revealed
significant water quality improvements,
including reductions in phosphorus, nitrates,
and total suspended solids. As a result of
water quality improvements, Valentine Mill
Pond was removed from the state's section
303(d) list in 2003. It now supports aquatic
life, serves as an agricultural water supply, and
offers aesthetic enjoyment.
Partners and Funding
The Nebraska DEQ provided the initial funding
for the NRD's diagnostic feasibility study.
However, the project would not have been
possible without the cooperation of the City
of Valentine, Nebraska Public Power District,
Cherry County, Nebraska Game and Parks
Commission, Nebraska Environmental Trust,
and Valentine Mill Pond landowners. The project
cost a total of $1.6 million, including $155,000
of Clean Water Act section 319 funding.
The hydrosuction sediment removal system lies
directly beneath the walkbridge shown here.
Valentine Mill Pond has been transformed from a
mud hole to a popular recreation area.
'. U.S. Environmental Protection Agency
\ Office of Water
a Washington, DC
EPA841-F-05-004F
June 2005
For additional information contact:
Mike Murphy
Middle Niobrara Natural Resources District
402-376-3241
Paul Brakhage
Nebraska Department of Environmental Quality
402-471-4224 • paul.brakhage@nebraska.gov
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