Agenda - Council - 10/27/2015 - Laserfiche WebLink

Home

D. Design Requirements The Ramsey SWMP has a dual purpose: 1) It will serve as a guide for the construction of storm drainage facilities, and 2) It will 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 problems under current 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 to accommodate the ultimate land use conditions 6. Recommendations for the revision of the current development ordinances 7. Recommendations for standard Operations and Maintenance procedures 8. Recommendations for specific construction site erosion control practices 9. Estimated construction and implementation costs of the SWMP 10. 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. Design of stormwater facilities shall be governed by Appendix E of the LRRWMO Third Generation Plan and City Code. These standards are summarized below: • Volume control — infiltration of the first 1 inch of runoff from all impervious surfaces on site. • Peak Flow Rate Control — Post Development peak runoff rates shall not exceed existing rates for the 2, 10 and 100 year storm peak discharges. • Water Quality — Storage areas shall be designed to NURP standards and provide annual removal efficiencies of 60% total phosphorus and 90% total suspended solids. • Precipitation Data Sources — rainfall amounts for hydrologic analyses shall be based on NOAA Atlas 14. • Storage Design — ponding areas shall be designed to retain the 100-year event. Ponding areas without a discharge shall be designed to retain runoff from the 100-year/10-day runoff or 100-year/10-day snowmelt, whichever is more restrictive. Section IV October 21, 2015 Page 31