Agenda - Environmental Policy Board - 03/02/2015

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Updated Storm Water Management Plan (SWMP) City of Ramsey, Minnesota X. SUMMARY AND RECOMMENDATIONS A. Summary The Ramsey SWMP has a dual purpose: it will serve as a guide for the construction of storm drainage facilities and provide a basis for a consistent approach to the preservation of lakes, wetlands, streams, and the Mississippi and Rum Rivers. The following issues have been incorporated into this plan: 1. Division of the City into major watersheds based on contour maps, grading plans and natural topography 2. Determination of storm water runoff under ultimate land use conditions 3. General layout and sizing of trunk storm sewers and open channels 4. Tributary areas, storage volumes, and high water levels of all existing ponding areas 5. Recommendations for the revision of the current development ordinances 6. Recommendations for standard Operations and Maintenance procedures 7. Recommendations for specific construction site erosion control practices 8. Estimated construction and implementation costs of the SWMP 9. Recommendations for education of City residents, staff, and development community. The primary function of an urban storm drainage system is to minimize economic loss and inconvenience due to periodic flooding of streets and other low-lying areas. Adequately designed storm drainage facilities provide flood control, minimize hazards and inconvenience associated with flooding, and protect or enhance water quality. The SWMP takes the entire drainage basin with future saturation development into consideration. Wet water quality ponds upstream or dry regional infiltration basins (where possible) will help control the rate and the volume of storm water runoff. To provide flood protection for adjacent property, the design storm interval for ponding areas with a known outfall is a 100 -year storm as compared to a 10 -year storm for design of storm sewer piping. For land locked ponds or wetlands, the design storm interval is a back-to-back 100 -year storm or the 100 -year, 10 -day snow melt event, whichever is larger. Any new residential, commercial, industrial and other habitable structures shall be constructed with the following low floor elevation: Elevation of the lowest floor of a structure shall be a minimum of 1 foot above the Emergency Overflow, or 2 feet above the HWL of the nearby pond or waterbody, whichever is higher. In areas adjacent to designated flood plains as mapped on a Flood Insurance Rate Map, the Regulatory Flood Protection Elevation (RFE) applies. The RFE is defined as the mapped 100 -year flood elevation plus 1 foot. However, the LRRWMO requires that the lowest floor elevation be 2 feet above the calculated flood elevation. Therefore, all structures, including accessory structures, must be elevated on fill so that the lowest floor including basement floor is at or above the Regulatory Flood Protection Elevation or 2 foot above the mapped 100 -year flood elevation. The finished fill elevation for structures shall be no lower than the Regulatory Flood Protection Elevation and the fill shall extend Section X February 20, 2015March 6, 2015 Page 64