2004.05.03 ORD 2004-386, 387, 388

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RULE C: STORM©WATER MANAGEMENT PLANS POLICY. It is the policy of the Board of Managers to: (a) Manage stormwater and snowmelt runoff on a regional or subwatershed basis and promote natural infiltration of runoff throughout the District to: (1) Provide effective water quality treatment and where possible provide such treatment prior to discharge to surface waterbodies and wetlands. (2) Ensure that future peak rates of runoff are less than or equal to existing rates. (3) Maximize infiltration and control runoff volume increase. (b) Require stormwater facilities to be ,constructed on individual sites where regional facilities are not available. 2. REGULATION. A permit and stormwater management plan is required under this rule for new development, redevelopment, or additions to an existing site. 3. DESIGN CRITERIA FOR STORMWATER MANAGEMENT PLANS. Stormwater management plans must comply with the following criteria: (a) A hydrograph method based on sound hydrologic theory must be used to analyze stormwater runoff for the design or analysis of flows and water levels within and off the project site. (b) Stormwater runoff rates for the proposed project must not exceed pre project runoff rates for the critical one-year or two-year and 100 -year frequency events. (c) Regional detention basins will be utilized to manage peak flow rates and meet water quality objectives where possible. On site detention basins will be utilized when regional basins are not in place or are not feasible. (d) Analysis of flood levels, storage volumes, and flow rates for waterbodies and detention basins must be based on the range of rainfall and snow melt durations which produces the critical (highest) flood levels and discharges. (e) Detention basins must be designed to provide: (1) An outlet structure to control the one-year or two-year and 100 -year frequency events to pre -project peak runoff rates. (2) An identified overflow spillway sufficiently stabilized to convey flows greater than the 100 -year critical storm event. (3) Access for future maintenance. (f) Permanent sedimentation and water quality ponds are required and must be designed to provide: (1) Water quality features consistent with NURP criteria and District wet pond criteria (see appendix (2) A permanent wet pool with dead storage of at least equal to the runoff from a 2.5 rainfall over the area tributary to the pond. (3) An outlet structure capable of preventing migration of floating debris and oils for at least the one-year storm. (4) Access for future maintenance. (g) The proposed project must not adversely affect water levels off the site during or after construction (h) Stormwater Management Plans under this rule must conform with approved Municipal Stormwater Management Plans.