12/18/2013 Env Bd Packet - Laserfiche WebLink

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17.8 Require project proposers to disperse outflow from stormwater management facilities to prevent erosion and failure of outlet structures. Make attempts to simulate sheet flow at these locations as opposed to concentrated flows. 17.9 Require project proposers to use conservation development design and /or low impact development techniques, and ecological stormwater management techniques. 17.10 Require project proposers to limit the amount and connectedness of impervious surfaces and direct runoff into vegetated landscape areas including swales, prairies, and other infiltration. 17.11 Require project proposers to use stormwater management techniques that encourage infiltration of stormwater runoff and groundwater recharge, whenever possible, to maximize the infiltration potential of the site. Sizing criteria for SMAs are designed to support large infiltrating surfaces or wetland complexes. To create conditions appropriate for these two types of stormwater management features, SMAs within the AUAR area must have: • no more than 20% of their surface area as permanent open water; the remaining surface area of each SMA shall contain mesic prairie or wet prairie plant communities to maximize the infiltration and water quality treatment capacities of the system. • design high water levels (100 -Year) less than or equal to 2.5 feet above the normal water level or lowest outlet invert. • side slopes that are less than or equal to 6:1, horizontal to vertical, and a 10:1 safety bench at the normal water level per RCWD requirements. The following is a list of additional stormwater management recommendations: • Adhere to surface area recommendations for stormwater management (Figure 17 -3). • During site design, follow low impact development practices, such as increased open space, disconnected and minimized impervious surfaces, capitalizing on high infiltration capacity soils, and dispersed stormwater management. • In residential development areas, use of a combination of side and rear lot drainage easements that are no -mow zones planted with formal or informal native landscaping. The rear lot areas would be designed for infiltration, and side lot areas would be designed for effective drainage and conveyance of water from around foundations to ensure no standing water remains adjacent to the houses. • Route driveway, sidewalk and gutter downspout waters into rain gardens and infiltration areas. This can be accomplished without compromising 6