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Updated Surface Water Management Plan (SWMP) <br />City of Ramsey, Minnesota <br />D. Design Requirements <br />The Ramsey SWMP has a dual purpose: 1) It will serve as a guide for the construction of <br />storm drainage facilities, and 2) It will provide a basis for a consistent approach to the <br />preservation of lakes, wetlands, streams, and the Mississippi and Rum Rivers. The <br />following issues have been incorporated into this plan: <br />1. Division of the City into major watersheds based on contour maps, grading plans <br />and natural topography <br />2. Determination of storm water runoff problems under current land use conditions <br />3. General layout and sizing of trunk storm sewers and open channels <br />4. Tributary areas, storage volumes, and high water levels of all existing ponding <br />areas <br />5. Recommendations to accommodate the ultimate land use conditions <br />6. Recommendations for the revision of the current development ordinances <br />7. Recommendations for standard Operations and Maintenance procedures <br />8. Recommendations for specific construction site erosion control practices <br />9. Estimated construction and implementation costs of the SWMP <br />10. Recommendations for education of City residents, staff, and development <br />community. <br />The primary function of an urban storm drainage system is to minimize economic loss <br />and inconvenience due to periodic flooding of streets and other low-lying areas. <br />Adequately designed storm drainage facilities provide flood control, minimize hazards <br />and inconvenience associated with flooding, and protect or enhance water quality. The <br />SWMP takes the entire drainage basin with future saturation development into <br />consideration. <br />Design of stormwater facilities shall be governed by Appendix E of the LRRWMO Third <br />Generation Plan and City Code. These standards are summarized below: <br />• Volume control — infiltration of the first 1 inch of runoff from all impervious <br />surfaces on site. <br />• Peak Flow Rate Control — Post Development peak runoff rates shall not exceed <br />existing rates for the 2, 10 and 100 year storm peak discharges. <br />• Water Quality — Storage areas shall be designed to NURP standards and provide <br />annual removal efficiencies of 60% total phosphorus and 90% total suspended <br />solids. <br />• Precipitation Data Sources — rainfall amounts for hydrologic analyses shall be <br />based on NOAA Atlas 14. <br />• Storage Design — ponding areas shall be designed to retain the 100-year event. <br />Ponding areas without a discharge shall be designed to retain runoff from the <br />100-year/10-day runoff or 100-year/10-day snowmelt, whichever is more <br />restrictive. <br />Section IV <br />October 21, 2015 Page 31 <br />