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TO: <br />FROM: <br />DATE: <br />SUBJECT: <br />CALCULATIONS <br />Vegetated Swales <br />MEMORANDUM <br />Kirk Brooks <br />-lane Zimmerman <br />March 18, 1992 <br />Plan Review, SEPA 12-92 <br />Current City standards call for vegetated swales to be <br />designed for the 2 year, 24 hour storm peak discharge, with <br />higher flows diverted around the swale. If possible, the <br />swales should be designed with a bypass system. A possible <br />arrangement for the bypass pipe is sketched in on sheet C-1. <br />The swale should then be designed per the following criteria <br />for the 2 year, 24-hour storm: <br />"n$, = 0.12 <br />max velocity = 1.5 feet per second <br />max. depth = 0.5 feet <br />If diversion is not feasible, the following additional <br />design criteria will apply for the 25 year, 24-hour storm: <br />"n" = 0.035 <br />max velocity = 4.0 feet per second <br />max. depth = 1.0 feet <br />a <br />Vegetated swales: <br />Spot elevations in the bottom of the swale should be given <br />at the head of the swale, at the swale outlet, and at <br />approximately 50 foot intervals along the length of the <br />swale. <br />The plans should specify construction of the swale per <br />section 4.15.1.2 of the City of Everett's Design and <br />Construction Standards and Specifications. The swale seed <br />and plant list from page IV-17 of the City's standards <br />should also be included on the plans. <br />