7211 RAINIER DR BASE FILE 2018-01-01 MF Import

/ �1 PUBL/C WOR/ffS , � � MEMORANDUM TO: Kirk Brooks FROM: Jane Zimmern�an DATE: July 12, 1995 SUgJECT; Drainage Calculation Review, Bridge Creek Townhomes, SEPA N18-95 A planimetered (or otherwise generated) elevation to surface area relationship for the pond/vault must be submitted to the City, to allow the City to generate the pondlvault's stage-storage volume relationship for routing calculations. From the stage-storage relationship of the pond/vault, the stage at which the City's required detention volume will be reached must be noted. The pond's overflow elevation must be set at this elevation. The 6 month, 24-hour developed srorm must be routed through the pond\vault with a 1 inch orifice as the primary outlet. The amount of]ive storage thai "backs up" must be determined, and subtracted from the wetpond design volume (the wetpond design volume is '_'001 cubic feet, as determined from the 6 month, 24-hour developed storm hydrograph volume) to determine the required dead storage volume. This required dead storage volume must be provided below the outlet elevation of the pond. A minimum of 15% of the wetpond design volume (or 300 cubic feet) must be provided in the wetpond treatment cell, at a maximum average water depth of 1.33 feet. The rest of the dead storage volume may be provided in the vault upstream of the pond. The 6 month, 24-hour developed storm hydrograph must be routed through the pond\vault and the peak stage in the pond must be noted. A secondary orifice must be located at this elevation.