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RCWD RCE CREEK WATERSHED DISTRICT PROJECT DESCRIPTION & INTENT In 2002, Peltier Lake was listed as impaired by the Minnesota Pollution Control Agency (MPCA) and placed on the 303(d) list. The impairment is based on excess phosphorus, which creates more frequent and more intense algae blooms. Algae blooms interfere with recreation, and negatively impact ecological health. In 2013, a total maximum daily load (TMDL) was approved by the MPCA and the US Environmental Protection Agency (USEPA) for Peltier Lake (EOR, 2013). The TMDL indicates that the majority of phosphorus loading to Peltier Lake is occurring internally. The internal phosphorus loading contributes to plant and algae growth. This cycle reoccurs on an annual basis. The TMDL identifies a plant, curlyleaf pondweed, as a contributor to internal loading of phosphorus. One of the projects identified in the TMDL is a water level drawdown. Performing the drawdown over the winter months can kill curlyleaf pondweed turions by exposing them to freezing and desiccation. Turions are buds that deposit on the lake bottom and are able to grow into a new plant during the next season. Additionally, drawing down the lake consolidates exposed sediments, promoting the germination and rooting of healthy, native plant seeds rather than nuisance plants such as curlyleaf pondweed and Eurasian watermilFoil. i In 2015, the Rice Creek Watershed District (RCWD) retained Houston Engineering, Inc. (HEI) to conduct a feasibility study for the drawdown of Peltier Lake (HEI, 2015). The study included the analysis of three drawdown scenarios. 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. Each scenario produced in a different drawdown level. The feasibility analysis examined 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 involves only removing the stop logs in the lake dam outlet structure and allowing the lake level to drop approximately 3 feet. The drawdown is proposed to occur in the fall of 2016, following the aquatic recreation season, and continue through the winter into the spring of 2017. Once the stop logs are removed, the lake will take approximately 51 days to drawdown to its target (design) elevation, anticipated to be approximately 882 feet NAVD88. This drawdown elevation is based on hydraulic modeling of the removal of the stop logs in the dam outlet structure. The drawdown time could be affected by any rain events that occur during the drawdown, which would increase the drawdown time. Once the lake has reached its final drawdown elevation, approximately 200 acres (34%) of the lake bottom area will be exposed along the shoreline. Figure 1 shows estimates of the footprint of the water surface at both the ordinary high water (OHW) elevation (884.88 NAVD88) and at the proposed drawdown elevation (882.06 NAVD88). The OHW is similar to a "typicar level during the spring. Based on plant surveys performed by the RCWD, the drawdown will expose a significant portion of the shoreline lake bottom affected by curlyleaf pondweed. Once the lake and shoreline freeze during the winter season, exposed cudyleaf pondweed plants and turions within the exposed sediment will freeze, desiccate, and be unable to regrow during the next summer season. Fish will be protected from winterkill by an aeration system operated by Anoka County Parks. Once ice -out occurs in the spring, the stop logs will be placed back in the dam outlet structure and the lake inflow from Rice Creek will begin to gradually refill the lake. The lake will very likely refill within a few weeks, dependent upon the amount of snowmelt and the size of spring rainfall events occurring during the refill period. Once the lake has refilled, the dam will continue to function as normal. The effect of the drawdown on curlyleaf pondweed abundance, algal blooms, and overall water quality will be monitored over the 2017 season to assess the success of the drawdown. The current proposal is a one-time occurrence. However, as the results of 1 115