Hannen Lake - Impaired Waters List

Posted: 7/30/2009
Benton / Hannen Lake Park

(from a earlier story in the Vinton Eagle).

On April 30, 2009, the Iowa Department of Natural Resources (DNR) submitted a list of "439 waterbodies with a total of 581 impairments" to the Environmental Protection Agency (EPA) for approval.

Hannen Lake, in southern Benton County, is on the draft list of impaired waters.

According to Iowa DNR, "most of the impairments on Iowa’s draft list of impaired waters, however, do not indicate severely or grossly polluted conditions...Many waters assessed as “impaired” for aquatic life uses often continue to support a moderately diverse aquatic community."

Last evening, during a regular meeting of the Benton County Conservation Board (BCCB), Kate Timmerman from the Natural Resource Conservation Service (NRCS) briefed the board about the Hannen Lake Watershed Project problem. She revealed that Hannen, a man-made lake, was built in 1960 with a depth of 27.5 feet and had a surface area of 49 acres; today, maximum depth is 21 feet and surface area has decreased to 37 acres. She related the lake has been dredged (i.e., silt was removed from the lake bottom) in the 1980's and again in 2004.

The water quality problems at Hannen Lake are related to increased phosphorus levels leading to high pH, and algae growth (e.g., algae blooms which turn the surface of the waterbody green).

Sources of Phosphorus: The goal is to eliminate the phosphorus from entering the watershed, there are several related and interacting potential sources.

1. Upwind Erosion. Erosion from lands within and adjacent to the watershed are potential sources of phosphorous. Rangeland management practices may be contributing factors.
2. Shoreline Erosion. Preexisting and recent agricultural sediments contribute to rises in phosphorus from wave and wind action.
3. Internal Recycling. Existing sediment on the bottom of Hannen Lake from wind action and mixing from bottom-feeding fish(e.g., carp and catfish) contribute to the phosphorus problem.

Fixing the Problem: Improving water quality to ensure the health of the Hannen Lake watershed can be accomplished by taking a three-point approach:

1. Structural Practices: Since a portion of the phosphorus comes from wave action along the shoreline a structural remedy would include riprap (i.e., rocks to stabilize the shoreline). The NRCS representative indicated the importance of shoreline stabilization and indicated the Iowa DNR provides as 75% cost-share grant. This means, if the Benton CCB comes up with the first ~$42,000 to pay for the project the county will be reimbursed 75% and will ultimately only pay 25% (~$6,600) for the project.
2. Wetland Enhancements: Agricultural run-off from adjacent properties, particularly rangeland practices, will be lessened by wetland enhancing projects. Planting rooted water plants (e.g., buttercup and water lotus) in wetland areas will help capture the phosphorus.
3. Dredging: After the first two steps are accomplished within the alloted timeframe, the BCCB will be eligible for DNR funded dredging.

Completing these three steps in a timely manner is very important; however, without the full support of neighboring and adjacent landowners the phosphorus problems will continue despite the best efforts of the Benton County Conservation Board and the Natural Resource Conservation Service.

Additional information about environmental practices and contributions to the Hannen Lake Watershed restoration project should be directed to BCCB Director William Heber (319-472-4942).