1707 MERRILL CREEK PKY 2018-01-02 MF Import

! � preliminary stortn drain calculations, a l`10-year storm event during proposed develaped I coodidons will generate 14.58 cfs of stonnwater runoff. This flow will be treated prior to reaching our site, th:refore this flow shall be'intercxpted witttin our property boundary and rerouted within stormwater pipes direcdy to Mertill and Ring Cneek. � OQslte Drainage DescrfpUon: IDrainage leaving the site via Merrill and Ring Crcek continues notth for approzimately 1.2 mil;s and discharges into Possession Bay, which is located in Puget Sound. A typical I cross-section of Merrill and Ring Creek is trapezoidal in shape vith a bottom wi3th of approzimately 4 to 5 feet and 1:1 side slope. The stream channel is gendy sloped nnd the riparian zone consists of small hees and dense unde�rush. Durieg the site investigation � some slight bank sloughing and erosion were apparem. However, there is no evidence of inadequate capacity or oveRopping of the stream's banks. The stream was flowing at a depth of 8 inches and had approzimately 3 feet of freeboard at the time of inspection. � Conveyance System: . (_ The conveyance system is designed in accordance with the standar,ls oudined in the ' current Everott Stormwater Management Manual. As required, th� 25-year design storm event is used to deterniine the size of the stormwater pipes. Atta�:6ed is a table indicating catch basin collection aeeas and their respecdve pervious :a�d impervious areas. From � each of the catch basin's respecdve area, weighted "C" vaiues are obtained and used in the conveyance calculations. See the attached cone�yancc table to verify the proposed stortn drain system has adequa.e capacity to convcy the dev;loped flows on the site. � � � � ' ' 1 1 4 �