1716 W MARINE VIEW DR BASE FILE 2018-01-02 MF Import

I DEVELOPEL DRAINAGE CONDITION rAll stormwater conveyance systems have been sized to pass a 25-year design storm. All stormwater treatment systems are sized to divert the 6-month, 24-hour stormwater runoff. ' Detention systems to prevent downstream flooding are not provided because the downstream discharge location is the marina, which is directly connected to the Snohomish River. The proposed storm drainage piping system will collect runoff from the newly developed 3.4 acre site to an existing storm manhole serving Marina Village. A control structure will be place on the existing 30 inch storm main that services the Marina Village and South ' Marina Parking lots. This control structure will divert the 6-month, 24-hour stonnwater runoff to the city sanitary sewer system. Sanitary sewer will be prevented from backing into the storm system by a check valve. ' Stormwater greater then the 6-month, 24-hour storm from the new 3.4 acre site, the existing Marina Village, and the eastern two thirds of South Marina Parking lots will discharge into ' the existing outfall piping system. Invert elevations in the control structure used to divert stonnwater are also designed to prevent inflow of tidal waters into the storm and sanitary sewer systems. The storm sewcr system is designed to allow for the planned phased building construction. ' Catchments and piping for the northern portion of the project will be constrr.cted at a future date along with the related development. 1 I I