1131 RAINIER AVE 2016-01-01 MF Import

STORM DRAINAGE REPORT Projg�t Overview A 51 unit, 4 story apartment complex with associated parking is propo�e�i for a 1.304 acre parcel located on Rainier Avenue between Poplar and 12`h Street and approximately 1 mile south of the American Legion Memorial Pazk & Golf Course. More generally the site is located with the SE'/. of the NW '/. of Section 17, Township 27N, and Range SE of Williamette Meridian. �j�peConditioos The site is undeveloped with urban unmaintained grass cover. It is located within the 36'h Street Combined Drainage Basin. A portion of an existing building straddles the north property line at the NE comer of the site. The site slopes 1% downwazd from east to west. Current drainage from the site flows westward to Rainier Avenue where it enters the combined sewer/storm drain system. AeveloRed Conditions Construction of the apartment complex and the associated parking will create 0.797 acres of impervious area. Runoff from these impervious surfaces will be directed into a 48" CMP detention pipe. In accordance with the city of Everett Standazds, the detention pipe is designed to detain the 10 yeaz storm and release at the pre-developed 10 year rate. The discharge flow out of the pipe will be contxollcd by a flow restrictodoil pollution control device (FROP). The chart below lists the relevant discharge rates. ... ., ., . . ._;.,. . ...,,,. .. ., ..-. .,�: � ., . . .. ..... DESIGN PREDEVELOPED FLOW ` DEVELOPED FLO�V DEVELOPED FLOW STORI�: IN OUT . ------- ------- ------ -- ------ ------ -- ------- — __ - 10-YR, 24 HR 0.21 0.46 0.21 .. ... . . , _ . ., . . .,. ..., . . �.. ., . . . .,. .,. _ . ,.. . _ ....�.-.-..-.., . . .. Flow e�iting the detention system will be routed to a SSMH within Rainer Ave. RO�ti and Continue tivough the public combined Sanitary and Storm Sewer System 84-170-G