United States
                      Environmental Protection
                            Office Of Water
September 1995
Number 2
Watershed   Protection:
Clean  Lakes  Case  Study
Watershed   and  In-lake  Practices
Improve  Green  Valley  Lake,  Iowa
  Key Feature:

  Project Name:


  Land Type:

  Pollution Source:
  Data Sources:
  Data Mechanisms:

  Monitoring Plan:
  Control Measures:
 Impoundment heavily impacted by
 agricultural runoff
 Green Valley Lake
 Union County, Iowa
 USEPA Region 7
 Watershed Area 1946 ha
 Lake Area 158 ha
 Ecoregion #47,  western corn belt plains;
 planted in soybeans and corn
 Sediment, nutrients
 State; project monitoring
 Water quality and sediment sampling,
 bathymetric studies
 Sediment/nutrient retention dikes, grade
 stabilization structures, tile intake terraces,
 diversions, grassed waterways, sediment
 control basins
                                                           Figure 1. Location of Green Valley Lake in Iowa.
  Summary:  Green Valley Lake is a 158 ha impoundment located in
  southern Iowa.  It was built in 1952 near the headwaters of the Platte River and by the 1970s it was heavily impacted by
  erosion from its surrounding agricultural watershed. Soil and nutrients delivered to the lake produced a number of water
  quality problems including sedimentation, turbidity, excess growths of the blue-green algae Alphanizomenon sp., and low
  dissolved oxygen.  The algal blooms were responsible for early morning oxygen sags, which in turn led to partial kills of
  the largemouth bass and bluegill populations.

  All three phases of EPA's Section 314 Clean Lakes Program were implemented at Green Valley Lake. A Phase I
  Diagnostic/Feasibility Study identified the causes of the lake's water quality problems, and a Restoration/Implementation
  Project (Phase II of the Clean Lakes Program) was carried out in Green Valley Lake between 1980 and 1986. The
  Restoration Project included implementation of best management practices on surrounding agricultural lands and
  construction of sediment/nutrient retention dikes in the two major arms of the lake.  A total of 65 best management
  practice installation projects were completed, including grade stabilization structures, tile intake structures, a diversion,
  grassed waterways, terraces, and water sediment control basins. A monitoring program conducted during the Restoration
  phase indicated that water quality improved in the lake and the dikes  seemed to be effective in preventing the movement of
  sediments into the main lake.  The lake was monitored for three years to assess the benefits of the Restoration Project.
  Criteria for judging the effectiveness' of the Restoration Project were  established and included lowered suspended solids,
  lowered nutrients in lake inflows, and fewer algal blooms. The Clean Lakes Program Phase II Restoration Project largely
  succeeded with respect to these criteria. Additional monitoring conducted from 1991 to 1994 under a Phase III Clean
  Lakes Post-Restoration Monitoring Study indicates that Green Valley Lake has improved and probably will continue to
  improve due to both in-lake and watershed restoration efforts.
        Contact: Marion Conover, Chief, Fisheries Bureau, Iowa Department of Natural Resources, Wallace State
        Office Building, Des Moines, IA 50319-0034; phone 515-281-5208.

Green Valley Lake was formed as an impoundment of
the Platte River in 1952.  It lies just north of Creston,
Iowa, 88.5 kilometers southwest of Des Moines, Iowa,
and 137 kilometers east of Omaha, Nebraska (Figure 1).
It has a watershed area of 2105 hectares and a surface
area of 158 hectares.  The maximum depth of the lake is
7.9 meters and its hydraulic residence time is 1.82 years.
The area receives 84 cm of rain per year, 50 percent of
which falls between April and July, and 75 percent of
which falls during the April through October growing
season. Thunderstorms and other violent weather strike
the area on average 45 times per year.  The average
annual runoff for the watershed is 14 cm—6 cm in
surface runoff and 8 cm in subsurface runoff.

The entire  lake is surrounded by the Green Valley Lake
State Park, which is owned by the State of Iowa and
provides recreational opportunities for all citizens of the
state.  The land in the watershed is occupied by 39
landowners.  Seventy-two percent of the watershed is
farmed, primarily to raise corn and soybeans, and most
of the rest is parkland.

Water quality problems in Green Valley Lake first
became evident in the 1970s. Aquatic life and recreation
suffered from excessive inputs of sediment and nutrients.
Between 1968 and 1978 sedimentation reduced the lake
area by 10 percent and reduced the lake volume at a rate
of 8635 cubic meters per year.  Volume reduction was
most noticeable in the parts of the lake that received

In the northwest arm of the lake (inflow from the Platte
River), for instance, boating and fishing were eliminated
from over 10 hectares (6.3 percent of the lake surface)
because of the loss of lake volume and depth. High
turbidity was evident after rainfall, and wind alone was
enough to resuspend sediment in the shallows.

The lake  also received an overabundance  of nutrients.
Algal blooms occurred in summers and caused dissolved
oxygen (DO) sags in the morning hours.  These hi turn
caused partial fish kills and led to poor survival for
young-of-the-year fish.  The populations of largemouth
bass and  bluegills were reduced, and a bad taste and
 odor were noticed in fish caught in the lake, a typical
 phenomenon in lakes with algal blooms.  The algal
 blooms also  made the lake unsuitable and unattractive for
To address these problems, the Iowa Department of
Natural Resources (IDNR) enlisted and coordinated the
efforts of the following agencies:

US Environmental Protection Agency, Region 7, Kansas
  City, Kansas
USDA Natural Resources Conservation Service, Des
  Moines, Iowa
Iowa Department of Agriculture and Land Stewardship,
  Des Moines, Iowa
Union County Soil Conservation District, Creston, Iowa
Union County Consolidated Farm Service Agency,
  Creston, Iowa
Area Extension Office, Creston, Iowa
University Hygienic Laboratory, Iowa City
Participating landowners in Green Valley Lake

The Phase II Restoration Project officially lasted from
July 1980 to June 1986.

Based on the Phase I Diagnostic Study, the IDNR
established the following goals for the Green Valley
Lake Restoration Project:

(1) Reduce sediment/nutrient delivery to the lake to
    acceptable levels by installing best management
    practices (BMPs) on croplands in the watershed.
(2) Reduce resuspension of nutrients within the lake bed
    by deepening shallow water areas and/or containing
    such areas.
(3) Monitor chemical, physical, and biological
    parameters to detect changes in water quality.

 IDNR selected the following criteria to be used as
 evidence of an effective restoration of Green Valley

 (1) Improvements in water clarity or transparency
    measured with a Secchi disk.
 (2) Low suspended solids concentrations in the lake
    relative to other similar lakes.
 (3) Low levels of suspended solids and plant nutrients in
    the inflows relative to similar streams in the region.
 (4) Reductions in algal chlorophylls.
 (5) Reductions in blue-green algal populations.
 (6) Increases in public use of the State Park.

 IDNR administered the project.  In 1980, $569,100 in
 EPA Clean Lakes Program funds were received to
 implement Phase II restoration measures at Green Valley
 Lake. The Union County Soil Conservation District, in
 conjunction with landowners, prepared water quality
 management plans for individual farms surrounding the
 lake. Costs to implement the BMPs were shared by the
 Federal government (50 percent), the landowners
 (25 percent), and the  State (25 percent).  In-lake BMPs
 (sediment/nutrient retention dikes) were built by IDNR.
 Union County Soil Conservation District staff were
 funded by the Iowa Department of Agriculture and Land
 Stewardship and the USDA Natural Resources
 Conservation Service.

 Two approaches were used to restore the lake.  First,
 BMPs were installed on agricultural lands to reduce soil
 erosion. Figure 2 indicates the locations of BMPs in the
 surrounding watershed.  When the project ended, the
 following BMPs had been installed:  3 grade stabilization
 structures, 39 tile intake terraces (totaling 32,961 m),
 1 diversion (380 m long), 6 grassed waterways (totaling
 2946 m),  and 16 water sediment control basins. Second,
 two sediment/nutrient retention dikes were installed, one
 in each arm of the lake, to retard water  flow and cause
 sediment to settle out.  It was hoped that this would
 reduce sediment and nutrient  loads throughout the lake.
 Since 1987 additional BMPs,  including 4575 m of
 terraces and 15 water sediment control structures, have
 been added.  A separate crop set aside program had also
 reduced row cropland from 77 percent (of total cropland
 farmed in the  region) in 1980 to 60 percent by 1989.
 Green Valley Lake is classified to be used for primary
 and secondary contact recreation and as a drinking water
 supply.  The goal of the monitoring program for the
 Clean Lakes Project was to document short- and long-
 term trends in the lake resulting from the implementation
 of BMPs.  Monitoring data were collected for 6 years by
 the Iowa Department of Natural Resources and  Iowa
 State University.

 A bottom profile of the lake has been produced every
 5 years to determine the sedimentation rate.  Water
 quality samples were  taken during runoff events and dry
 weather.  Two in-lake monitoring sites were used.  The
 water was monitored  for pH, chlorophyll a, nitrogen,
 phosphorus, temperature, dissolved oxygen, total
 suspended solids, and Secchi disk transparency.
 Pesticides, metals, and fecal coliform levels were
 monitored in sediments  and the water column.  Water
 level, weed growth, fish kills, turbidity, and erosion
 were monitored as well, and fish populations were
 sampled twice each year to note any trends.  Lake use
 (recreation) data were also  collected.

Monitoring data collected during the 6-year project
indicated improvements were made in most of the
criteria for success that were established before the
project began (see Table 1). Somewhat surprisingly,
water clarity declined.  This problem was attributed to
an increase in populations of bullhead and carp, bottom-
dwelling fish species that stir up sediments in the course
of their daily activities.  This problem has been well-
documented in other Iowa lakes. Sediment  delivery was
reduced enough to lower lake volume loss from
8635 cubic meters/year in 1981 to 4318 cubic meters/
year in 1986, a result attributed to the sediment/nutrient
retention basins, grassed swales, and other BMPs.
Nitrogen levels decreased hi shallows, and phosphorus
levels decreased in shallows and depths.

The decline  in chlorophyll a was thought to  result from
reductions in phosphorus loadings.  Fewer algal blooms
occurred, and fewer complaints of bad odor and taste in
fish were received.  By 1986 the decrease in algae had
also led to a 50 percent decrease hi the daytime annual
mean level of DO to 5.7 mg/1 hi depths and 6.6 mg/1 hi
shallows and eliminated DO sags hi the morning hours.
As a result there were no summer fish kills  reported
after 1981.
Figure  2.   Watershed boundary  (perimeter)  and
areas where BMPs were installed (shaded) within the
Green Valley Lake watershed (IDNR).


Turbidity (JTU)
Secchi disk
transparency (cm)
Total P
s (mg/1) N02 +
Algal chlorophyll (//gflj
Blue-green algae
3 > Beach-use
(user days, x1 000)
Public use
complaints of fish taste & odor
no fish taste or odor complaints
4.7-fold increase in swimming
1 .5-fold increase in fishing
"doop sampling station (in-lake)/shallow sampling station (near inflow)
Table 1. Comparison of pre-restoration (1981) and post-restoration (1986) data and indicators of criteria for success at
Green Valley Lake.

The success of the Green Valley Lake Clean Lakes
Project can be measured in numerous ways, including
changes in water quality parameters. Improvements in
human and wildlife use of the lake were clearly
noticeable.  Swimming beach use at the lake more than
doubled between 1981-1986 as a result of the decrease in
blue-green algae populations (Figure 3).  Fishing hours
also increased 1.5-fold by 1986.
     D  2

                        83    84
 Figure 3.  Annual swimming beach use at Green
 Valley Lake (IDNR).

Costs and funding for the BMPs installed by landowners
and the state during the project are summarized in
Table 2.

Efforts to keep Greeri Valley Lake clean and healthy
continue since the completion of the Phase II Restoration
Project in 1986.  As indicated above, some additional
BMPs have been installed. Also, IDNR implemented an
EPA Clean Lakes Program Phase III Post-Restoration
Monitoring Project from 1991 to 1994.  The primary
objective of this monitoring was to determine if the
restoration techniques employed at Green Valley Lake
and within its watershed are working to improve the
lake's water quality.

Following are the types of monitoring activities that were

•   From May 1991 to April 1994 water quality was
   monitored  twice per month from May to September
   and once per month from October to April.

   Sediments  were sampled above and below the dikes to
   determine the dikes' sediment and nutrient removal

Grade stabilization structures
Tile intake terraces
Grassed waterways
Water sediment control basins
Number of BMPs
Amount Installed
3 structures
32,961 m
380 m
Cost/Funding ($)
Subtotal: 446,077.99
West sediment/nutrient retention dike
East sediment/nutrient retention dike
Total: 795,731.41
Federal Clean Lakes funding: 569,100.00
Non-Federal funding: 226,631.41
 Table 2. Costs and funding of BMP installation for the Green Valley Lake Clean Lakes Project (IDNR).
   Light penetration and wind speed and direction
   measurements were taken in the arms of the lake to
   evaluate resuspension of sediments due to wind

   Soil conservation practice activities were documented
   for the time period of the  project.

   Sediment basin maps were created for 1991 and 1994
   to estimate the lake sedimentation rate.

   Recreational use information was collected.
The final report on the Phase III Monitoring Program,
issued in June 1995, indicates that overall water quality
at Green Valley Lake has improved and probably will
continue to improve due to both in-lake and watershed
restoration efforts.  The Phase III study compared
current data (1991-1994) with historical data (1979,
1981-1986) and found that water quality at Green Valley
Lake, with natural fluctuations, has improved.  Also,
comparisons of water quality data from opposite sides of
the sediment/nutrient retention dikes support their role in
the improved quality of the lake.  As a result of the
improved water quality and fisheries at the lake, usership
has increased steadily over the past years.

(Anonymous).  1990. Phase III post-restoration
monitoring program on Green  Valley Lake, Union
County, Iowa.

Iowa Department of Natural Resources,  (undated).
Green  Valley Lake Clean Lakes Project.   Union County,
Iowa.  Six-year summary of activities. July 1980 - June

Iowa Department of Natural Resources. June 1995.
Phase III Project Final Report for Green Valley Lake,
Union  County, Iowa. 35pp.
   This case study  was prepared by Tetra Tech, Inc.,
   Fairfax, Virginia, in conjunction with EPA's Office of
   Wetlands, Oceans and Watersheds, Watershed Branch.
   To obtain a copy, contact your EPA Regional Clean
   Lakes Coordinator, or request a copy from:

   11029 Kenwood Road, Building 5
   Cincinnati, OH 45242
   FAX 513-489-8695



 — JD     —.
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