R2008-87 AUTHORIZING AGREEMENT - Laserfiche WebLink

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Recommendations: Improve Detention Basin Design 1. Encourage all municipalities or counties in the watershed to change their ordinances to reflect a more restricted release rate for the watershed. The drainage and stormwater management system should be designed to limit the peak discharge leaving the site to no more than .04 cfs/acre at a 2-year frequency, 24-hour duration storm event and .15 cfs/acre at a 100-year frequency, 24-hour duration storm event. 2. Incorporate a broader scale of detention basin design concepts to meet the primary benefits for stormwater and pollution management and as many secondary benefits as possible such as recreation, aesthetics, and habitat. • Encourage wet bottom detention basins for the purpose of improving water quality by capturing pollutants. • Wet detention basins should be deep enough to support fish and aquatic wildlife and allow for public use. • Dry detention basin should be designed to remove stormwater pollutants by having 80% of their bottom area with standing water no longer then 72 hours. • Incorporate functioning wetland areas. • Distance between detention inlets and outlets should be maximized. • Design wet basins with 3:1 shoreline slopes and native aquatic vegetation. 3. Require detention on all new development for commercial and industrial sites and residential dwellings of more than one residence per two-acre lot. . 4. Design a development so that small rainfall events would be collected from impervious surfaces (roofs, driveway, roads, sidewalks, etc)and flow into a rain garden to prevent stormwater from entering directly into storm sewers or road ditches. Incorporate Better Design Strategies for New and Redeveloped Sites 1. Reduce impervious surfaces with narrower streets, shorter driveways, narrower sidewalks, reduced parking space size, shared parking between adjacent user, shared parking between opposite peak businesses, and permeable paving. 2. Promote natural drainage with vegetated(Bio) swales planted with native grass species. 3. Establish filter strips or buffers. 4. Maintain open spaces for environmental benefits, wildlife, and recreation. Floodplains, wetlands, natural areas, or any open area can serve as open space. 5. Encourage infiltration practices such as infiltration trenches and basins. 6. Install filtration and biological treatments(i.e. constructed wetlands) 7. Manage runoff from road surfaces. 8. Introduce native trees, shrubs, grasses, and forbs. Preserve the 100-year Floodplain 1. Deter all construction or filling in of the FEMA 100-year mapped floodplain. Encourage the update of the current FEMA maps. 2. Discourage the placement of detention basins in the floodplain. 3. The placement of a detention basin in a flood fringe area should require compensatory storage for 1.5 times the volume below the base flood elevation occupied by the detention basin. 4. No reduction in existing floodway surface area. 5. Deter on-stream detention. 6. Preserve these areas as open space or natural areas planted with native species. Return floodplain to . original native vegetation. 9