1615 112TH ST SW 2016-01-01 MF Import

PRO.IECT OVGRVIG�V The following report presents thc design of a storm �vater detention system for the Shaw Creek Condomiums. The project site is located on the north side of 112th Street SW, approximatcly 900 fect west of SR-99, in the City of Everett. The 1.873 acre project site is presently developed with three duplcxes and associated outbuildings, on the cast side of the propeny. A pavcd driveway, 18 feet widc, 300 feet long provides aceess to the duplexes. Approximately 49 percent of the site is wooded. As shown on the conswction plans, the site will be developed with 12 new single-famil}' dwe:lling units. The existing duplexes will remain. Runoff from the driveway and new units will be conveyed in u storm drain pipe system to wet tank detention system located in the common access driveway. The system has been designed to release tlows at one-half the pre devcloped ratc for the 2 year storm as well ns release tlows nt the prc developed rates for the 10, and 100 year storms. "I�he design of the facilities meets current City requirements. Water quality for the development will be provided by 3 feet of dead storage in the bottom of detention pipe, as well as a vcgetated treatment cell at the outfall from the dclention tank.. The boundnries of the proposcd drainage urca tributury to thc detention system are delineated on the detention system drainage area map nt the end of this report. The "Waterworks" program wilh the Sanln Barbara Unit Hydrograph (SE3UH) met}�od and Type lA rainfall distribution was used in the design of Uie proposed facility. Control in the deten�ion system will be provided by the following set inside of a Type 11 Catch [3asin. . A 1.00-inch diameter orifice with an oudet elevation of 505.30. . A 3.25-inch diameter orifice with an outlet clevution of ?08.G0. . A I.00-inch diameter orifice �vith an outlet ele�ation of 509.10. A 12-inch diamter riser has been designed ta provide emergency ovcrflow. Thc detcntion pipe s�'stem ��'ill ou!fa11 to a�'egetatcd trcatment ccll designed in accordancc ��ith Cit� standards. U