RES 2025008 - Laserfiche WebLink

D. STORM WATER DRAINAGE The City stonn water drain system is composed primarily of curb inlets , underground pipes, local channels, natural swales and outfall devices. These facilities carry stonn water runoff within the drainage basin to flood control channels, locally known as arroyos. New development is required to install adequately sized stonn drain lines to connect to the City's overall drainage system. The authority for providing flood control service within the Plan Area lies with Zone 7 of the Alameda County Flood Control and Water Conservation District. Zone 7 has no existing or planned facilities within the Specific Plan Area. 1. Specific Plan Storm Draina2e Concept The proposed Plan Area stonn drainage concept is illustrated in Figure VI-4 and further discussed below. Development within the Specific Plan Area will result in an increase in impervious surface areas (building roofs, paved roadways, driveways , etc .). Undeveloped, vegetated lands generally have low runoff coefficients, meaning that they yield a relatively small portion of total rainfall as runoff. The majority of the precipitation, particularly in smaller stonns , infiltrates into the subsurface. Impervious surfaces yield nearly all rainfall as runoff. Increased runoff volumes could exceed the capacity of downstream drainage components causing localized flooding. The following measures will therefore be incorporated into the Plan to mitigate this potential impact: a. Each development project shall contribute to the cost of acqumng and constructing common storm water detention facilities located immediately upstream of several proposed outfalls to the Arroyo del Valle. These facilities shall be designed and engineered along with the Vineyard A venue real ignment improvements and may be aggregated for purposes of improving the efficiency of mitigation. Outfalls to the Arroyo shall be provided with appropriate easements, designed subject to City and County standards, and subject to approval by the owners of the land on which they are located. Drainage plans for projects to be developed in advance of the detention basins shall demonstrate that the proposed developments would minimize or eliminate increases in the volume or rate of runoff from the development sites during peak flow periods. b. A grading plan shall be submitted for review and approval by the Public Works Department as part of the development review process for each development, including individual vineyards within the Plan Area . The grading plan shall identify features for site drainage, runoff control, and best management practices for the control of erosion and sedimentation. 82