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Comparison of Ciry of Everett 3tandard Detention <br />Vault to Coaugated Metal Pipe Vault <br />December 2, 1994 <br />File No. 24-92-009-007-01 <br />Page 6 <br />For the vault at Sterling, Stokes Law may be simplified so that the pazticle must stay in the vault <br />long enough that its settling velocity (w) ���ill allo�v it to reach bottom before it exiu the vault, <br />or: <br />H < wtd <br />td = Q L (from above) <br />0 <br />H < wA�L <br />Qo <br />Settling rate for fine sand ranges from 30-80fdhr (Stormwater Management Table 7.3.). Using <br />30 ft/hr = .0083 ft/s: <br />For Approved Concrete Vault: <br />H�.0083ft/ x 140 ft2 x.125 fc = �S.95ft <br />1. cs <br />H=7.0' :. OK <br />For Proposed CMP Vault: <br />H<,0083f� x 46.6 ft2 x 170 ft _ 68.49ft <br />. cs <br />H = 7.0' :. OK <br />Scour needs to be looked at to ensure suspended pazticles aze not resuspended from the velocity <br />of the water flowing through the vault. <br />