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The following information regarding detention must be <br />submitted to the City for review and approval: <br />1) completed City of Everett Drainaqe Calculation <br />Form <br />2) orifice sizing calculations <br />3) stage-storage relationship of the pond <br />Wetoond/Detention: <br />If the applicant chooses to design the surPace pond as a <br />wetpond meeting City standards, the followinq comments are <br />standard to review of these facilitiea: <br />A completed City of Everett Drainage Calculation Form muat <br />be submitted, showing the required detention volume and the <br />allowable release rate. <br />The stage-storage relationship of the pond must also be <br />submitted to show that the pond has the capacity to store <br />the required wetpond volume anc9 the live detention volume. <br />The design wetpond volume must be reached or exceeded for <br />the 2 year, 24-hour storm. As a first guess, the primary <br />orifice should be sized to release approximately the <br />existinq 2 year storm peak and the second orifice located at <br />the elevation relating to the design wetpond volume. The 2 <br />year, 24-hour storm should then be routed through the pond <br />to verify that the wetpond design volume is being reached or <br />exceeded for the design storm. <br />The maximum storage in the wetpond (dead storage + live <br />storage) durinq the design storm (2 year, 24-hour storm) <br />must be equal to or greater than the calculated required <br />wetpond volume. The design storm must be routed throuqh the <br />pond to demonstrate that this requirement is being met, <br />unless the entire required wetpond volume is being provided <br />as dead storage. The minimum allowable orifice size for a <br />restrictor device associated with a wetpond is 1 inch. If a <br />1 inch orifice doesn't result in the required storage in the <br />pond, then the percentage of the required wetpond volume <br />provided as dead storage must be increased until the <br />requirement is satisfied. <br />The required volume of the wetponds must be determined <br />separately from detention volume. The required wetpond <br />volume is equal to the volume of runoff from the 2 year, 12- <br />hoi�r storm (1.20 inches of precipitation). Two methods are <br />.�cceptablP for determininq the required wet pond volume; <br />�•ither multiply the area of impervious surface in the <br />ccntributinq basin by 1.20 inches or determine the volume ��f <br />the 2 year, 24-hour hydrograph for the entire contributing <br />�irea and multiply by the ratio 1.20/1.55. At least 50$ of <br />