Laserfiche WebLink
_ Design Criteria and Methodology <br /> The City of Everett Storm Water Management Manual (2010 Version), was used as a <br /> minimum design standard for storm water conveyance system design. Per the manual <br /> pipes sizes were designed using the Rational Method to calculate peak flows. A <br /> minimum time of concentration of 5 minutes was assumed for the most upstream basin <br /> of each pipe run. <br /> The Storm Water Management Manual of Western Washington (dated August 12, 2012) <br /> was the guide used to design the pre-treatment vault. Western Washington Hydrology <br /> Model (2012) was used to determine the flow rate to be treated by the proposed CDS <br /> Stormceptor Vault and detention pond. <br /> Conveyance <br /> Pipes and outfall structures are designed for the 25-year storm event. A Manning's "n" <br /> of 0.013 was used in pipe design. <br /> , Existing downstream pipes are not evaluated. A detention pond is being proposed so <br /> downstream analysis was not completed <br /> Pre-Construction Conditions <br /> The total project site is 2.70 acres including portions of 15th Street and Winter Street. <br /> Basin "A" includes private land and areas in the public right-of-way that will be disturbed <br /> by construction. Existing development in the basin area consists of a variety of <br /> pavement surfaces, including portions of public roads, concrete foundations from <br /> previously removed structures, gravel areas, and landscaping. Runoff from Basin "A" <br /> currently infiltrates, drains into the public system, or drains into the ditches to the east <br /> and to the north of the project site. <br /> Basin "B" includes a portion of 15th Street, the adjacent sidewalk and landscaping. <br /> Runoff from Basin "B" currently drains into the public system or into the ditch north of <br /> the project site. Basin "B" lies outside of project limits and will not be disturbed by <br /> construction. Runoff within Basin "B" will be diverted into the detention pond post- <br /> construction to mitigate for portions of Basin "A" that will not be routed through the pre- <br /> treatment vault and detention pond. <br /> See the Pre-Construction Drainage Basin Map Appendix A for a pervious and <br /> impervious area summary. <br /> Post Construction Conditions <br /> When project construction is complete portions of 15th Street and Winter Street will be <br /> improved, a new office building constructed and the parking area rebuilt. The site will be <br /> March 05, 2015 <br /> - Hydrology Report — BNSF Everett Yard Office <br /> Page 6 of 8 <br />