8204 SPOKANE DR 2016-01-01 MF Import

TO: FROM: DATE: SUBJECT: PUBL/C WO/4/ffS . �,�� .. ., �� MEMORANDUM Cf,arLes Mor�a� i�irk-Breeks- Jane Zimmerman June 15, 1995 Fax - 3y 8- t3 � 3=1- Drainage Calculation Review, Broadway South Condominiums �'2 To demonstrate that the wetpond meets City standards, the wetoond design storm must be routed through the pond, and the peak storage during the storm, including live and dead storage, must be equal to the wetpond d�sign volume. The wetpond design storm is the 6 month, 24-hour storm. If half of the wetpond design volume is provided as dead storage, the other half of the volume (2408 cubic feet) must be backed up in the pond during the wetpond design storm. When the 6 month, 24-hour storm is routed through the pond as currentiy designed, i�sufficient live storage resulu. Even when the primary orifice is reduced to the minimum allowed 1 inch size, only 1922 cubic feet of storage is obtained during the 6 month, 24-hour storm. Therefore, the dead storage in the pond must be increased by 486 cubic feet, so that the combined peak live storage during the storm and the dead storage volume equal the wetpond design volume of 4816 cubic feet. If the stage-tive storage relationship of the pond is not changed by the addition of dead storage volume, a secondary orifice of 4.25 inches located at elevation 514.23 feet would allow the pond to meet both detention and wetpond requirements. If the stage- live storage of the pond is changed, routing calculations and orifice sizing calculations will need to be redone. The secondary orifice is placed at the maximum storage elevation during the 6 month, 24-hour storm and is sized so that the combined discharge from the primary and secondary orifices is equal to the allowable discharge (0.65 cfs) when the pond reaches the overflow elevation.