2018-03-14 CC Packet - Laserfiche WebLink

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shoreline banks and exposed tree roots. About a dozen small trees (6" - 12" DBH) are holding the bank in place, but many of the trees are slumping into the lake. A sanitary sewer line parallels the lakeshore along this north zone, generally within 5' —20' of the eroding shoreline. This sewer main is at risk of failure if the lakeshore erosion trend continues. An emergency repair was recently completed where the sanitary sewer line was already exposed because of the lakeshore erosion. Riprap was installed along 16 linear feet of shoreline in the north zone of Phase 2 South Zone (Approximately 149 ) —The south zone is characterized by steep shoreline banks (about 2:1). The crown of the shoreline is generally 3' —4' above the OHWL and then the topography flattens into about a 10' wide bench. Shoreline erosion has undercut this level area, resulting in 3' —4' high shoreline banks. A sanitary sewer line parallels the lakeshore along this south zone, generally within 5' — 10' of the eroding shoreline. This sewer main is at risk of failure if the lakeshore erosion trend continues. PROJECT DESIGN Trail Side Park Phase 2 is located on the windward side of Centerville Lake and experiences more than a mile of fetch. On windy days, the shoreline is pounded by waves more than a foot high. The Trail Side Park Phase 2 shoreline also absorbs the wakes from recreational boaters, including waterskiing events held offshore from the park. With a goal of long term shoreline stabilization, the Anoka Conservation District proposes installing riprap (the minimal quantity necessary) and native shrubs. North Zone (Approximately 179 ) - The north zone design consists of laying type IV geotextile fabric under 12 inches of riprap (the minimal depth feasible for shoreline protection) that is keyed into the lake bottom. On average, the riprap will be 6' wide and will be installed to the crown of the lakeshore bank. Low growing native shrubs, such as redosier dogwood, will be installed in clusters above the riprap in areas that are not on top of the sanitary sewer main. South Zone (Approximately 149 ) —The south zone design consists of laying type IV geotextile fabric under 12 inches of riprap (the minimal depth feasible for shoreline protection) that is keyed into the lake bottom. On average, the riprap will be 8' wide and will be installed to the crown of the lakeshore bank. Low growing native shrubs, such as redosier dogwood, will be installed in clusters above the riprap in areas that are not on top of the sanitary sewer main. Please note minor regrading of the bank was considered in this zone zone in an attempt to limit the maximum elevation of the riprap. However, the proximity of the sanitary sewer line to the top of the bank and the desire to preserve existing trees made the regrading infeasible. PROJECT BENEFITS Water Quality Stabilization of the Trail Side Park Phase 2 shoreline will provide reductions in total suspended solids, total phosphorus, and other nutrients entering Centerville Lake. As part of the Rice Creek Chain of Lakes system, the water quality benefits will also have downstream benefits to the Chain of Lakes and Rice Creek. Page 2 of 6 15