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STAFF REPORT <br />TO:Mayor Keis and Members of City Council <br />FROM:Bill Dircks, Public Works Director <br />DATE:December 12, 2019 <br />RE:Twin Lake Outlet Update <br />At its meeting on December 11, the Ramsey Washington Metro Watershed District Board heard the <br />flood risk mitigation feasibility study put together by Barr Engineering. The study was very thorough <br />and contained a lot of information regarding the history of the lake, County Ditch 16, and MnDOT <br />interstate projects. The study can be found in the Board’s agenda packet for the meeting here. <br />The study narrowed the potential solutions down to four alternatives and those were thoroughly <br />researched and discussed. The four alternatives were: <br />1.Purchase the flood-prone structure and remove it. <br />2.Develop an emergency response plan, which would be similar to how things were handled this <br />past summer. <br />3.Install a gravity outlet at 874.0. <br />4.Install a gravity outlet at 872.2. <br />Based on the evaluation of the four alternatives the study recommended Alternative 4, gravity outlet at <br />872.2 as the most feasible flood-risk mitigation alternative. The outlet would be a ditch from the <br />wetland northeast of Waldo Pond into a gravity pipe with a gate valve through the existing <br />embankment of Waldo Pond. This alternative would include a detailed operations plan that would <br />describe when the valve could be opened and when it could be closed since there is the risk of flooding <br />downstream in Gervais Lake and the Phalen Chain. The operations plan would reduce the risk. The <br />operations plan involves City staff operating the valve and potentially maintaining the ditch. Staff <br />estimates that there will be approximately eight hours of maintenance per year with the ditch, pipe, and <br />valve. <br />The Board authorized Barr Engineering and Watershed staff to move forward with final design of <br />alternative 4. As the design progresses some of the finer details will be sorted out. The 30-year <br />estimated cost range of alternative 4 is $267,000 with a range of $214,000 to $401,000. The estimated <br />cost of construction is $226,000 with a range of $181,000 to $339,000. The project will be paid for by <br />the Watershed District. The timeline calls for the final design to be ready by February, bidding in <br />February/March, and construction starting in the spring.