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, <br /> , Pacific Topsoils Riverside site�tortn Drainage Report <br /> GFK ConsulGng Inc. <br /> 5 Stormwater water quality system design <br /> As described above, the water quality design for this site will consist of a bio swale. To assure <br /> that all of the nanoff generated by the paved area is collected and passes thru the entire <br /> swale, a curb will be installed along the top of the bio swale side parallel to the existing <br /> pavement. This way runoff intercepted by the swale will be diverted to the lowest comer of the <br /> site to be collected within a Catch Basin and conveyed to the top or intet uf the bio swale. <br /> 5.1 Bio Swale design <br /> Section 3-4 of the City of Everett 1997 Stormwater Management Manual outlines the design <br /> criteria for a bio-swale. From SBUH the 6 month Type 1A water quality event for the entire <br /> paved area is 0.844 cfs (see appendix). Because flows above the water quality design flow <br /> will be allowed to flow thru the bio swale it is considered an "on-line"facility. Calculations <br /> using the W1NHM3 for water quality predict a water quality treatment runoff of 0.60 cfs. <br /> Figures 9.6 a, Volume 5 of the DOE manual supplies a correction factor of 1.5 for converting <br /> 1NWHM water quality vali�::s to SBUH at a 1.12inR�r rainfall intensity. Applying this to the <br /> 1NWHM3 runoff value provides a corrected runoff rate of 0.90 cfs which is the more <br /> conservative value and will be used for analysis of the bio-swale design. <br /> Due to the terrain and location of the drainage ditches, it is assumed that the flows across the <br /> paved section will be split approximately equally between the two side conveyances. As a <br /> result, the biaswale design will be based on a flow of 0.45cfs. The designed bio swale has a <br /> 3' base with 3:1 side slopes and a channel slope of 0.5% for 100', and an n value of 0.24 <br /> (assumes low maintenance), this configuration results in a flow depth of 5.76" at 0.210 fps for <br /> the design flow of 0.45cfs, and yields a residence time of 7.92 minutes. This meets the <br /> criteria set out in The COE Manual for a bio swale with emergent plantings. <br /> sas�. <br /> rqu� oawn <br /> q�ds) O.DO 0.45 <br /> n O.�SO D.YSD <br /> B(ly 3.00 �.OD Trsp. <br /> LfSbpe 3.00 3.00 <br /> RSSbp 3.0� 7.�0 <br /> y(11) 0.48 0.48 <br /> S(ftM) 0.005 0.005 <br /> Lfly t00.0U0 100.000 <br /> t�m�) c.000 �.�o <br /> A�sQ 2113 <br /> P��p Q018 V�RIs) 0.210 <br /> R(R) 0.36� <br /> Jab: Pacfic Tapsoik Rwrtide slla dsorpL�: Bb Srle wM qiWily Ilor <br /> gy; � DaM: B120'2010 <br /> �\ <br /> 8/20/2010 8 / �j / <br /> C:\Project data\Project files\PTopsoils Rlverside sitelReports\Riverside4.doc � � <br />