1707 MERRILL CREEK PKY 2018-01-02 MF Import

i ' Flow Control and Water Quallty Facilitl�: � Flow control and water qualiry design standards for the site are in accordance with the C'ity of Everett Sturm Water Management Manual (C6apter 3) dated January 1997. The ' Greens of Merrill l'reek project will be required to provide sour�ce contrul, stream bank erosion control and runoff tru^aunent, due to the creation of more than 5,000 square feet of impervious and pollution generating surfaces (Sce aCached table 1-1.1). IThe City of Everett StoRn Water Management Manual requires detendon to limit the peak developed dischazge rate for the 2-year, 24-hour storm event to not exceed 50% of the peak runoff rate for the 2-yeaz, 24-hour storm under the predevloped con3itions. In , addition, die peak developed runoff rates for the 10-yeaz and the 100-yeaz, 24hour design stonn events are not to exceed the peak tunoff r,ues for the 10-yeaz and 100-year I storms under ezisting site conditions. The Santa Barbzra Urban Hydrograph method is used to estimate runoff for the site. A cornxtion factor is required when SCS-type methods and the 24-hour storm durations are used to design streambank erosion ' measures. The correction factor increases the required detention volume to account for the effects of continual storm events. The correction factor to be used in the design of runoff control is determined frum Figure 1-3.1. See the attachei Figure 1-3.1. � Water quality will be achieved through the consuvction of a wetpond that will consist of a permanent pool volume equal to the volume of runoff from a 6-month, 24-hour design � storm. 7'he 6-month, 24 hour design storm is determined from the developed site conditions. The wetpond will be.composed of two cells, the open water cell and the wetland treatment cell. A maaimum of 85% of the permanent pool volume will be � associated with the open water cell which is to be loe:ated within the detention/wet vault. A minimum of 15% of the permanent pool volume must be associateci with the wedand treatment cell and must be vegeta[ed. T'he detention volume pive srorage) will be 1 combined with the wetpond open water cell volume (dead storage) in order�� reduce the � number of vaults necessary to contro] the site's stortn water. � The attached calculations used to size the detention and water quality facilities for the site show a required detention volume of 62,659 cubic feet with a toW of 62,816 cubic feet provided within the actual vault. The required volume for water quality is 20,270 cubic � feet. The maximum required volume in the wet vault is 17,229 cubic feet and the minimum required wetpond volume is 3,041 cubic feet, with 17,280 cubic feet located within the vault and 3,041 cubic feet within the wetpond. ' Seaway Lot 8, which is located to the south of Merrill Creek Pazkway, contributes off- site flows to the project site through an 18" conerete pipe. Seaway lot 8 consists of 35.45 ' acres and is located within two drainage basins, the Merrill and Ring Creek and Glenwood Creek drainage basins. The Merrill and Ring Creek drainage basin collects � 23.28 acres of flow and the Glenwuod Creek drainage basi� accounts for the other 12.17 acres of flow generated on the site. The Merrill and Ring Creek basin associated with Seaway lot 8 is conveyed through the project site while the runoff generated within IGlenwood Creek basin is conveyed elsewhere. According to W & H Pacific's ( 3 �