7.5 SR 06-01-2020 - Laserfiche WebLink

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City of Elk River May 15, 2020 Page 2 1.2. Project Location This project will be constructed in selected areas above the Lake Orono Dam. A map showing the specific location of the improvements to be constructed is included in Appendix A. 2.0 ANALYSIS OF NECESSISTY Since 1998, several past projects, studies, technical evaluations, lake monitoring and citizen input have demonstrated the need and necessity for this project. Specific information in support of the necessity of this project is further provided in the following paragraphs. In 1998, the City removed approximately 120,000 cubic yards of sediment from the lake. An Environmental Assessment Worksheet was completed for that project. As part of this work, sedimentation studies predicted in 20 years. the lake would again require sediment removal based on continued sediment accumulation in the lake. This project need is consistent with that anticipated schedule. Throughout the past years, the City has worked with regulating agencies and interested parties regarding the proposed improvements to Lake Orono. These parties have included the Sherburne Soil and Water Conservation District, the MN Department of Natural Resources, the US Army Corps of Engineers, the Lake Orono Improvement Association, the State Historic Preservation Office, as well as interested citizens. These agencies have shown support of this project. The City has completed studies regarding estimated sediment volumes and suspension, accumulation rates, contaminants analysis and phosphorous loading. These studies indicate lake habitat will be enhanced by the implementation of this project. Over the past years, meetings have been held with the Lake Orono Improvement Association (LOIA) representatives (residents) who have been strong advocates for this project moving forward. The City has received comments and concerns from this organization as well as other users of the lake indicating that navigation and recreational opportunities have been restricted on the lake by accumulation of sediment in recent years. Shallow water depths, poor water clarity/quality and an abundance of curly leaf pondweed were consistent concerns. This project is anticipated to address many of these concerns. In 2011, a study was undertaken to determine the extent to which additional sediment had been deposited in the lake since the dredging project was completed in 1998. The results of this study were presented in a 2011 memorandum prepared by Wenck and Associates, which documents extensive sedimentation had occurred and supports the need for the project. This memorandum is included in Appendix A of this document. The Wenck document estimated that approximately 70,000 cubic yards of sediment had been deposited in the basin over the 11 years between 1999 and 2010 and noted a sediment deposition rate ranging from 6,400 to 6,900 cubic yards per year. The study indicated the functions and values of the lake related to a wide variety of uses had been significantly impaired due to the sediment deposition It was recommended that to restore these functions and values, a future sediment removal project could be undertaken.