1717 W CASINO RD 2018-01-01 MF Import

� I/ � Puecic w�oRKs MEMORANDUM 1'O: Al Locke/Gordon Witcher F[IOM: Jane Zimmerman DATE: August 15, 1997 SUBJECT: Drainage Calsulation Review for Creckside Apartments, SEPA M96-53 Resvictor devices may have a minimum orifice size of 1 inch. Because the site is so small, and due to the City's minimum orifice size requirements, it appears that separate roof-top runoff and pavement runoff detention systems arc not feasible. Therefore, all runoff must be combined together and routed through a common control structure for the provision of stormwater detention. Pavement runoff must be treated in a wetpond meeting Ciry standards. Even though treatment of roof-top runoff is not required, if the roof-top runoff is combined wilh thc pavement runoff before the pavement runoff has been treated, then the wetpond must be sized to meet City standards for the entire contributing area, including roof-tops. Wetpond calculations are required. The engineer may choose to usc the City's current standards, or the standards in effect at the titnc of SEPA approval may be used instead. The City's current standards are found in the City's Stormwater Management Manual. Design of the wetpond in accordance with the old slandards would generate the following comments: The wetpond desiga volume is equal to the volume of runoff from the 6 month, 24-hour stortn. The following two methods are acceptabie for determining the wetpond design volumc: I) nmltiply the area of impervious surface in the contributing basin by the precipitation assceiated with the design stortn, or 2) determine the total volume of stormwater runoff from contributing areas (impervious and pervious) using the Santa Barbara Urban Hydrograph method or comparable method.