Restoration Accomplishments

"Five Island Lake is an excellent example for a dredging project for three reasons: 1) an extremely low sedimentation rate; 2) public participation; and 3) low cost" according to Roger Bachmann, a world renowned limnologist at Iowa State University.

Five Island Lake restoration project has unique features that separates it from all other lake restoration endeavors.

First is the community support in donation of time and money. The initial bond issue of $400,000 passed by 90% in a community of 4,500 inhabitants. The total contribution of the community to date exceeds $1,200,000.

Second, the dredging aspect of our program is the largest ever of a natural lake in the United States. In the lower 600 acres of this lake, the water level will be deepened from its former 4 to 6 feet to 14 to 16 feet with several areas dredged to over 20 feet. When finished, at least 4,500,000 cubic yards of silt will have been removed. Size was not the original objective, but because of the extensive dredging, this project will serve as a laboratory to determine what can be accomplished by the large scale removal of silt. Our water monitoring data to date demonstrates in Area 5 where 85% of the silt has been removed compared to Area 1 which has not been dredged, a lessening of suspended solids, total phosphorus, and chlorophyll "a" and an increased measurement in the Secchi disk depth--all indications of improved water quality.

Third, our costs are much lower than similar endeavors by the government. We believe our costs will be approximately 50 cents a cubic yard of silt removed. Most government dredging operations are at least $2.00 a cubic yard. We are able to do this because we own our own dredge and hire our own employees. Although we have an experienced project manager, many of the tasks that government would pay for are donated by Lake Board members and other citizens. For example, legal work is extensive because of numerous contracts for silt deposit sites, but legal fees have been minimal.

Fourth, we have the oldest volunteer lake monitoring program in Iowa. Our main goal is improved water quality. To check our progress we have been collecting water samples as stated above since 1991. The chemical analysis is performed at the Civil Engineering Laboratory at Iowa State University using EPA approved methods. We expect to continue this program for at least three years after dredging ceases.

Lastly, the duration of benefits will last for hundreds of years. In 1993, Iowa State University studied Five Island Lake and our project. The year 1993 was noted for the large amount of rainfall, but even during that year Iowa State's measurement of silt running back into the lake was 0.2 inches per year, one of the lowest siltation rates of any lake in Iowa. Since we are lowering the silt bed by 10 1/2 feet or 126 inches, calculations indicate our efforts will last for at least 600 years.

Results

Below are two diagrams that succinctly illustrate the extent of the siltation problem in Five Island Lake when this project began. Below it is a second diagram which illustrates what we have accomplished to date. These are not cross-sectional diagrams of the lake but are water levels and silt levels from south to north the five-mile length of the lake.

Five Island Lake Before Restoration. This map demonstrates the predominance of silt volume over water volume in the Five Island Lake bed. This drawing was made in 1935 but the same conditions were present in 1989 when the present project began. Water this shallow is useless for recreational purposes.

Five Island Lake As It Exists Now. The removal of silt by hydraulic dredging, accompanied by shoreline stabilization and watershed management has removed 5,000,000 cubic yards of silt and replaced this with water. Water clarity has markedly improved.