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2017-05-10 CC Packet
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2017-05-10 CC Packet
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RCWD <br />RCE CREEK WATERSHED DISTRICT <br />PROJECT DESCRIPTION & INTENT <br />In 2002, Peltier Lake was listed as impaired by the Minnesota Pollution Control Agency (MPCA) and placed on <br />the 303(d) list. The impairment is based on excess phosphorus, which creates more frequent and more intense <br />algae blooms. Algae blooms interfere with recreation, and negatively impact ecological health. In 2013, a total <br />maximum daily load (TMDL) was approved by the MPCA and the US Environmental Protection Agency <br />(USEPA) for Peltier Lake (EOR, 2013). The TMDL indicates that the majority of phosphorus loading to Peltier <br />Lake is occurring internally. The internal phosphorus loading contributes to plant and algae growth. This cycle <br />reoccurs on an annual basis. The TMDL identifies a plant, curlyleaf pondweed, as a contributor to internal <br />loading of phosphorus. One of the projects identified in the TMDL is a water level drawdown. Performing the <br />drawdown over the winter months can kill curlyleaf pondweed turions by exposing them to freezing and <br />desiccation. Turions are buds that deposit on the lake bottom and are able to grow into a new plant during the <br />next season. Additionally, drawing down the lake consolidates exposed sediments, promoting the germination <br />and rooting of healthy, native plant seeds rather than nuisance plants such as curlyleaf pondweed and Eurasian <br />watermilFoil. <br />i <br />In 2015, the Rice Creek Watershed District (RCWD) retained Houston Engineering, Inc. (HEI) to conduct a <br />feasibility study for the drawdown of Peltier Lake (HEI, 2015). The study included the analysis of three <br />drawdown scenarios. The scenarios ranged from simply removing the stop logs at the dam outlet structure to <br />removing the stop logs combined with various degrees of pumping water from the lake, over the dam. Each <br />scenario produced in a different drawdown level. The feasibility analysis examined drawdown effects on <br />downstream elevation and flows, probable oxygen depletion in Peltier Lake, and cost to achieve the drawdown. <br />The scenario ultimately chosen for the drawdown involves only removing the stop logs in the lake dam outlet <br />structure and allowing the lake level to drop approximately 3 feet. <br />The drawdown is proposed to occur in the fall of 2016, following the aquatic recreation season, and continue <br />through the winter into the spring of 2017. Once the stop logs are removed, the lake will take approximately 51 <br />days to drawdown to its target (design) elevation, anticipated to be approximately 882 feet NAVD88. This <br />drawdown elevation is based on hydraulic modeling of the removal of the stop logs in the dam outlet structure. <br />The drawdown time could be affected by any rain events that occur during the drawdown, which would increase <br />the drawdown time. Once the lake has reached its final drawdown elevation, approximately 200 acres (34%) of <br />the lake bottom area will be exposed along the shoreline. Figure 1 shows estimates of the footprint of the water <br />surface at both the ordinary high water (OHW) elevation (884.88 NAVD88) and at the proposed drawdown <br />elevation (882.06 NAVD88). The OHW is similar to a "typicar level during the spring. Based on plant surveys <br />performed by the RCWD, the drawdown will expose a significant portion of the shoreline lake bottom affected by <br />curlyleaf pondweed. Once the lake and shoreline freeze during the winter season, exposed cudyleaf pondweed <br />plants and turions within the exposed sediment will freeze, desiccate, and be unable to regrow during the next <br />summer season. Fish will be protected from winterkill by an aeration system operated by Anoka County Parks. <br />Once ice -out occurs in the spring, the stop logs will be placed back in the dam outlet structure and the lake <br />inflow from Rice Creek will begin to gradually refill the lake. The lake will very likely refill within a few weeks, <br />dependent upon the amount of snowmelt and the size of spring rainfall events occurring during the refill period. <br />Once the lake has refilled, the dam will continue to function as normal. The effect of the drawdown on curlyleaf <br />pondweed abundance, algal blooms, and overall water quality will be monitored over the 2017 season to <br />assess the success of the drawdown. The current proposal is a one-time occurrence. However, as the results of <br />1 <br />115 <br />
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