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Draina e Calculations <br /> Calculations should be submitted showing that the open water <br /> cells contain no more than 40$ of the wetpond�s permanent <br /> storage, by volume and that other City standards for <br /> wetlands are being met. <br /> Current City standards call for vegetated swales to be <br /> designed for the 2 year, 24 hour storm peak discharqe, with <br /> higher flows diverted around the swale. However, diversion <br /> doea not appear feasible in this case. Therefore, the <br /> following design criteria will apply: <br /> 2 year, 24-hour storm: "n" = 0. 12 <br /> max velocity = 1. 5 feet per second <br /> max. depth = 0. 5 feet <br /> 25 year, 24-hour storm: "n" = 0.035 <br /> max velocity = 4 . 0 feet per second <br /> max. depth = 1. 0 feet <br /> Calculations showing that the swales meet the City design <br /> criteria regarding depths of flow, velocities of flow and <br /> length requirements should be submitted. Current <br /> calculations are for the 10 year storm, and the flow depths <br /> shown exceed City standards. Information as to the amount <br /> of paved surfaces contributing runoff to each swale and the <br /> required length of swale (per City standards) should also be <br /> submitted. <br /> The required volume of the wetponds must be determined <br /> separately from detention. The required � etpond volume is <br /> equal to the volume of runoff from the 2 year, 12 hour storm <br /> (1.20 inches of precipitation) . Two methods are acceptable <br /> for determining the required wet pond volume; either <br /> multiply the area of impervious surface in the contributing <br /> basin by 1.2o inches or determine the volume of the 2 year, <br /> 12 hour hydrograph for the contributing area. Half of this <br /> volume is required to be permanent storage in the pond. The <br /> required detention volume must be provided as live storage <br /> in addition to the dead storage. The control structure must <br /> ensure that detention release rates do n�t exceed allowable <br /> release rates and that the detained volume in the pond <br /> equals the required wet pond volume for the 2 year storm. <br /> The stage-storaqe relationship for the pond should be <br /> developed and submitted to allow the City to verify orifice <br /> elevations. <br />