New Project: Assessing Effectiveness of Pond Sediment Removal for Phosphorus Management in Stormwater Ponds

MnDOT manages rainwater runoff to keep pollutants like phosphorus from Minnesota’s lakes and streams. Stormwater retention ponds, an established management strategy, allow phosphorus to settle to the pond’s bottom but do require periodic cleanout.

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While dredging ponds of accumulated sediments restores stormwater detention capacity, it is unclear how much phosphorus may be released from the disturbed sediment into the pond’s water. Watershed and pond characteristics such as age, tree cover and surrounding land use can also impact the flux of the phosphorus sediment to the pond water.

Maintenance measures such as treating the sediment may help maintain appropriate pond phosphorus concentrations. An understanding of sediment removal impacts on phosphorus release will enable pond management strategies to reduce phosphorus release into surrounding lakes and waterways.

“This project will help us understand how sediment dredging in different stormwater ponds may impact the pond’s water quality protection function,” said Derek Asche, water resource engineer, City of Maple Grove. “More effective management of our stormwater ponds can further protect Minnesota’s lakes and streams.”

Objectives

In a new project, researchers will determine how removing sediment from stormwater ponds impacts the release of sediment phosphorus and resulting water quality in ponds with varying characteristics.

The objectives are:

Analyze sediment phosphorus release rates and water quality in six ponds before and after dredging projects
Monitor pond conditions and water quality during the growing season before and after pond maintenance
Quantify various phosphorus forms in sediment cores to assess the potential of undredged compared to dredged sediments to release phosphorus
Consider the impact of chemical sediment treatments to control phosphorus concentrations in stormwater ponds