Background

In 2002, Peltier Lake was listed as impaired for nutrients/eutrophication. The 2013 total maximum daily load (TMDL) for this impairment identified internal phosphorus loading as the primary source, with the macrophyte curly-leaf pondweed as a primary contributor to internal loading of phosphorus. Implementation strategies identified in the TMDL included drawing down the lake to specifically target the reduction of curly-leaf pondweed.

The Project

In 2015, Houston Engineering, Inc. (HEI) was retained by the Rice Creek Watershed District (RCWD) to conduct a feasibility study for the drawdown of Peltier Lake. The study included the analysis of three drawdown scenarios designed to expose curly-leaf pondweed turions on the lake bottom to winter freeze conditions, thus reducing their phosphorus contribution to the lake. The scenarios ranged from simply removing the stop logs at the dam outlet structure to removing the stop logs combined with various degrees of pumping water from the lake over the dam. The feasibility analysis examined drawdown time, drawdown effects on downstream elevation and flows, probable oxygen depletion in Peltier Lake, and cost to achieve the drawdown.

The scenario ultimately chosen for the drawdown involved only removing the stop logs in the lake dam outlet structure and allowing the lake level to drop approximately 3 feet.

HEI assisted the RCWD in coordinating the drawdown with the public and various stakeholders, including the Public Water permit with the Minnesota Department of Natural Resources and landowners.

HEI also developed the drawdown procedure and aided the RCWD during the drawdown and continued monitoring of the drawdown progress.