09/02/2008 Council Packet - Laserfiche WebLink

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• • • o The other two storm sewer lines discharge to the large wetland complex. No channels are known from this wetland to the lake, thus urban nutrient loads are not directly discharging to Rice Lake. If there is an interest in nutrient load reduction to this wetland, then infiltration BMPs would need to be integrated into the conveyance system. • On the far southeast the storm sewer conveyance system discharges to a pond and then the fringing wetland. The pond outlet is channelized to the lake and shows negligible interaction with the fringing wetland. Nutrient loading may be reduced by optimizing the wetland and channel interaction and should be investigated. • The two sensitive water level points in the south Rice Lake neighborhood are at ponds, and all wetlands in the neighborhood are already being used for stormwater. Urban retrofit (on site volume control measures) is most likely the only alternative for reducing the potential for flooding at the two pond locations. • The runoff from the northwest portion of this subwatershed drains to the sensitive wetlands located in catchment RLA -021 on the north side of Lake Drive. Decreasing stormwater flows to these wetlands would be beneficial to restoration. • The northwest portion of this subwatershed is located on very sandy soils that are currently underutilized for stormwater infiltration. The projects shown on the map are a few of the possible locations that could be used for larger scale infiltration practices. A feasibility study that finalizes potential locations and completes a preliminary evaluation of the final sites is the next step in quantifying the potential for retrofit (on site volume control measures) projects in this area. At this point the RMP standards and these projects are sufficient to provide protection for the wetlands with high stormwater impact potential on the northwest side of the lake. George Watch RMU Existing Conditions Recommendations • George Watch Lake is being investigated for excess nutrient loading as part of the Chain of Lakes TMDL. Once the nutrient reduction goal is established, watershed -based measures to reduce the inputs from the direct drainage area can be formulated. Several important groundwater - dependent wetland complexes are found in the drainage area. • North of 35W and south of Oak Lane is an important wetland complex with coniferous and hardwood swamps and alder thickets. These classifications are a signature for groundwater inputs, and so maintenance will rely upon knowledge of the local groundwater. Stormwater discharge to these wetlands will alter the chemistry and eliminate the characteristic vegetation. Stormwater management should not include this wetland in a system of pipes and ponds. The existing stormwater conveyance system along Lake Dr NE discharges to a pond that outlets to a channel and ultimately enters this wetland complex. Measures should be taken to reduce stormwater conveyance by implementing a network of BMPs in the conveyance area. • North of 35W and north of Oak Lane is a larger wetland complex dominated by alder thicket, a moderate indicator of groundwater. There is no pipe and pond system discharging to this wetland and planning should employ alternative stormwater management systems (i.e., not a pipe and pond system). 10 -17