Agenda - Parks and Recreation Commission - 05/08/2003

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landscape theme that incorporates a mixture of dry prairie, oak savanna, and wet prair/e with an ephemeral water-way could serve as the cornerstone for this area and provide a valuable lirzk between RTC and Mississippi West Regional Park. O~Site ~Xet/and ~Jitigation Two additional areas have been identified for off-site wetland mitigation i.n the event on- site mitigation is sot feasible. These sites are illustrated in Figure 12.5. Site #1 would be within the Mississippi Regional Park when develoPment of the park proceeds. Although a speciSc location cannot be identLfied at this time, the City, WMO and County would work. together to select and develop a site that would b. ol.d the 'best potential for successful wedand establishment. Fignzre i2.{5 illustrares the Anoka County · Park Deparm~ent's concept for how the Park will be designed. Several locations could be possible sites for incorporation of "new" wetland. To accomplish this action in the future, RTc LLC would need to escrow an amount o'f funds sufficient to construct the additional wetland acreage not provided for on-site. Site #2 is located along the south - southeast side of Lake Itasca on land already owned by the City ofRamsey. Th/s area c,arrently contains some excellent quality shrub swamp, wet prairie and emergent marsh along the shores of Lake Itasca. A suitable site could be located where wetland does not currently exist, but where adequate hydrology is available. There are also several areas of reed canary-dominated wetland that could be improved for public value credit though re-establishment of native wetland communities. Any wetland improvements in this area could be desired to also improve Btanding'~ turtle habitat. The following are proposed to mitigate impacts associated with the stormwater ouffall to the Mississippi Pdver: Reduce Frequency of Stormwater Discharge, Lower ~v[agnitude of Peak Flow Rates: The RTC project incorporates a var/eD' of strategies to lower increases in stormwater rate and volume. Wh/le all stormwater conveyance features are designed to accommodate the 100-year runoff event without tak/ng in.filtration into consideration, on-site retention and infiltration can be incorporated at multiple scales into the RTC during the. detailed design phase for smaller storm retention. Peak flow rates for the 100-year, 24-hour runoff and 100-year, 10-day snowraelt events are 25.1 c£s and 25.3 cfs respectively. Oversize Culvert and Reduced Slope at OutfalL' The last section of' culvert will 'be enlarged from 21-inches to 36-inches and include an apron and rip-rap to lower velocities and dissipate the energy at the discharge point. This will minimize the potential for scour and erosion. Directional Boring to Install Culvert: IX possible, the culvert will be placed within ;the river bank by directional boring rather than an open cut. This will reduce the need to remove shoreline vegetation and will minimize the area o£disturbance. Erosion control measures Mil be implemented where soil is disturbed. All disturbed areas will be 16 D-7-