Agenda - Environmental Policy Board - 03/02/2015

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Updated Storm Water Management Plan (SWMP) City of Ramsey, Minnesota Policy 1.5: Major storm water facilities (i.e., ponds, pond outlet systems, and major conveyance systems) will be designed using a return period of 100 years. Policy 1.6: The peak outflow from all new developments shall be limited to 75 percent of the existing peak outflow for the 2-, 10- and 100 - year SCS 24-hour rainfall events. Policy 1.7: All minor drainage system analyses and design (i.e., piped collection systems and minor conveyance systems) will be based on a return period of 10 years unless otherwise specified. The minor drainage system pipe will be sized using the full gravity flow capacity of the pipe. Pressure flow based on surcharging the upstream manhole or structure to near the street will not be allowed. Policy 1.8: Detention facility design will include a paved access route or a "Netlon" or approved equal stabilized access route; and dedicated right-of-way, outlot access and/or drainage and utility easement for maintenance of the outlet structure and to the facility in general. Policy 1.9: Fences will be restricted from crossing drainage and utility easements. Policy 1.10: The design of storm water facilities will consider and identify location(s) of overflow(s) that prevent property damage to adjacent properties from extreme water levels. Policy 1.11: Minimum building elevations should be above designed of designated flood levels. The minimum building floor elevation shall be two (2) feet above the 100 -year level or 1 -foot above the EOF. The 100 -year level shall be on the highest 100 -year level resulting from a single event analysis; the 100 -year, 10 -day snowmelt event; a multiple day runoff event analysis, or the critical event analysis. Policy 1.12: Landlocked runoff basins shall be sized to handle back-to-back 100 -year 8CS-Atlas14 24-hour rainfall events, the 10 -inch SCS 24-hour rainfall event or the 100 -year, 10 -day snowmelt snow melt event, whichever produces the higher peak pond elevation (Landlocked HWL). The minimum building floor elevation around landlocked basins shall be two (2) feet above the Landlocked HWL. Policy 1.13: Emergency overflows or outlets to drainage systems will be provided to any landlocked area if the available storm water storage capacity is inadequate to prevent flooding of residences and if the available downstream conveyance system capacity is adequate to accept additional flow. Policy 1.14: The City will have standard hydrologic design criteria for all storm water systems to assure consistency. Section V February 20, 2015March 6, 2015 Page 39