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Updated Storm Water Management Plan (SWMP) <br />City of Ramsey, Minnesota <br />Ten -Day Snow Melt Runoff with Type "C" Distribution (100-Year/10-day snow <br />melt runoff): A modeled runoff event that represents snowmelt conditions over a 10 -day <br />period for a return period snow depth of 100 years. The runoff event is simulated for a <br />curve number (CN) of 100 which represents frozen soil conditions or where all surfaces <br />are considered impervious. For some Ramsey the ten-day runoff event is critical event for <br />identifying the high water level of the basin or water body because the Anoka Sand Plain <br />typically reduces runoff under unfrozen conditions. The Type C distribution is similar in <br />concept to the Type I and II distributions, and for this event, establishes the time <br />distribution of runoff volume over the ten-day period. <br />Treatment Volume (Vt): The volume of storm water runoff that is treated within a BMP <br />or IMP storm water treatment facility. Typically the volume is expressed in terms of <br />inches of runoff per impervious acre. <br />Type I, IA, II and III Storm Distributions - NRCS: These storm types represent the <br />time distribution of a 24-hour rainfall event for areas throughout the United States. The <br />total storm depth is distributed according to the diagram in subpart A. Type II storms are <br />more "flashy" (i.e., convective/thunderstorms) than a Type I or IA storm. Subpart B <br />illustrates that all of Minnesota is within the Type II rainfall distribution area. <br />Section XI <br />February 20, 2015March 6, 2015 Page 84 <br />