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<br />Updated Storm Water Management Plan (SWMP) <br />City of Ramsey, Minnesota <br /> <br />This report recommends modifying the current development ordinances to <br />encourage infiltration and soil ripping of mass grading to compensate for lost <br />infiltration conditions as well" as requiring oversized retention ponding to mitigate <br />and compensate for increases in runoff. Innovative solutions to the storm water <br />runoff increases associated with the increase in impervious surface will be <br />. investigated and encouraged when deemed appropriate. Potential solutions <br />include pervious pavements, rain gardens, infiltration basins and low impact <br />development among others. <br /> <br />2. An integral part of this SWMP is the comprehensive storm water runoff <br />modeling of the existing conditions throughout the entire city. This modeling <br />includes: <br /> <br />a. Mapping out the small watersheds draining to general collection points <br />such as low points in roadways and intersections, wetlands or ponds. . <br /> <br />b. Estimating the runoff from the 2, 10 and lOO-year rainfall events. <br /> <br />c. Routing the runoff through the existing system. <br /> <br />The existing system may be a pipe network, a pond, a wetland or a waterway. <br />Themodeling predicts the high water levels and flows associated with each <br />rainfall event modeled. <br /> <br />This modeling will provide a baseline for comparison purposes as new <br />developments change the drainage pattern. With this modeling information, City <br />staff can readily review the cumulative impacts oflarge developments for effects <br />on the baseline conditions across the entire watershed. <br /> <br />StonnNET software was used in the comprehensive modeling. This software is <br />based on the industry standard EPASWMM process and the St. Vennant <br />equations. The model can be used to input actual rainfall events from rain <br />gauges and can model the transport of pollutants through the system. This will <br />be very useful in evaluating the BMP measures to address future TMDLs. <br /> <br />3. Where the cumulative effect of regulated development is potential flooding, the <br />recommended practice is the construction of retention ponds or detention basins, <br />including infiltration, as a requirement of further development of the outlying <br />growth areas. It is further recommended that the post construction peak outflows <br />from new developments be limited to no more than 75 percent of the existing <br />peak flow for the 2-, 10-, and 100-yearstorms. This will better mitigate the <br />cumulative effects of increased impervious surfacing and increased runoff <br />volume from new developments. <br /> <br />M13.39530 <br />October 13, 2008 <br /> <br />ro Bolton & Menk. Inc. 2008. All Rights Reserved <br />Section II <br /> <br />Page 5 <br /> <br />-197- <br />