Easter Lake Watershed Project Sediment Forebay and Stormwater Wetland
This project will coincide with the implementation of the Easter Lake Watershed Management Plan to improve water quality and includes two major components, a sediment basin forebay and a stormwater wetland. These practices will work together to reduce sediment and stormwater pollutants from entering Easter Lake, in the Des Moines River Watershed, where a primarily urban drainage area has contributed to lake sedimentation and high nutrient levels.
Polk Soil & Water Conservation District has worked closely with Polk County Conservation Board who is both a project partner and landowner for this Water Quality Initiative Urban Conservation Project. This request is composed of two major components, a sediment basin forebay and a stormwater wetland. These practices will work together to reduce sediment and stormwater pollutants from entering Easter Lake, in the Des Moines River Watershed, where a 37 acre primarily urban drainage area is causing significant lake sedimentation and high nutrient levels. For this proposed project, drainage water will first enter the sediment basin where suspended sediment will be captured decreasing turbidity and insoluble phosphorous levels. Drainage water will then flow through the stormwater wetland where soluble nutrients and other pollutants will be removed before entering Easter Lake.
Constructed wetlands provide quantity control of stormwater by providing a significant volume of temporary water storage above the permanent pool elevation. As stormwater runoff flows through the wetland, pollutant removal is achieved by settling and biological uptake within the practice. By designing a wetland similar to nutrient reduction wetlands used on agricultural lands to address nitrates from tile discharge we hope to see similar benefits of anaerobic bacteria breaking down and removing nitrates. Designs will include rock weirs or earth berms to extend the water flow path and maximize residency time, further increasing anaerobic activity. If funded we will suggest that our designers consult with IDALS engineers to ensure the wetland design achieves the 45% reduction of nitrates targeted in the Nutrient Reduction Strategy. Wetlands are among the most effective stormwater practices in terms of pollutant removal, and also offer aesthetic value. A sediment forebay is provided for removal of course sediments that could degrade performance.