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1 <br />V <br />SOUNDVIEW TECHNOLOGY CENTER EVERETT, WA <br />Basin B <br />This drainage Basin B is conveyed to a steep ravine that intersects the property along the northern <br />property line. The ravine has signs of surface flow at the low point. The stormwater is then conveyed along <br />the forested Swale, where it intersects a home built wall which crosses the flow path. This wall is shown in <br />the photo 4 below. <br />Just below this wall, a homemade 2 foot wide swale was constructed in the natural low point of the swale <br />to convey stormwater. This swale was rimmed on both sides with concrete test cylinders (see photo 5) <br />with minor tree debris was observed in the swale. The stormwater is conveyed within this swale for <br />approximately 60', and then discharges back to a more natural forest Swale. The approximate slope of <br />this Swale is 20%. The stormwater then continues down in the natural swale until entering a 15" diameter <br />culvert on the south side of Debrelon Lane. The culvert opening was clear at the time of the downstream <br />analysis. <br />The storm water is conveyed through catch basins for approximately 300 feet, and connects to a plastic <br />storm pipe outlet. This pipe outlets to a catch basin with grate. See picture 6 below. This catch basin <br />connects to the existing 18-inch culvert under Lamar Drive where it discharges into the ravine above <br />Edgewater Creek to the northeast. At this point the downstream field reconnaissance has ended at the'/a <br />mile point. <br />One potential problem of this basin outfall is the private wall constructed across the forest swale. Per an <br />older downstream analysis prepared by Datum Pacific, there is a 12" CSP culvert underneath this wall <br />connecting the forest swale with the 2' wide created swale. This could not be verified in the field. There <br />are two 4" concrete pipes that outfall at the base of the wall, but since no inlet for these pipes could be <br />found it can be assumed that they are there for sub -drainage behind the wall. There was evidence of <br />water traveling around the eastern side of the wall to get to the ditch. <br />Since this project will detain the release rates to the predeveloped release rates in excess of the release <br />rates required for the project (0.5 CFS max. discharge to this basin), no additional measures are proposed <br />and the release flows will be dispersed on -site at the low point of the Swale. <br />Basin B --Photo <br />Description <br />:( <br />N'Concrete <br />test cylinder <br />IMAY 23, 2017 STORMWATER DRAINAGE REPORT PAGE 11 <br />