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Recommendations: <br /> Improve Detention Basin Design <br /> 1. Encourage all municipalities or counties in the watershed to change their ordinances to reflect a more <br /> restricted release rate for the watershed. The drainage and stormwater management system should be <br /> designed to limit the peak discharge leaving the site to no more than .04 cfs/acre at a 2-year <br /> frequency, 24-hour duration storm event and .15 cfs/acre at a 100-year frequency, 24-hour duration <br /> storm event. <br /> 2. Incorporate a broader scale of detention basin design concepts to meet the primary benefits for <br /> stormwater and pollution management and as many secondary benefits as possible such as recreation, <br /> aesthetics, and habitat. <br /> • Encourage wet bottom detention basins for the purpose of improving water quality by capturing <br /> pollutants. <br /> • Wet detention basins should be deep enough to support fish and aquatic wildlife and allow for <br /> public use. ', <br /> • Dry detention basin should be designed to remove stormwater pollutants by having 80%of their <br /> bottom area with standing water no longer then 72 hours. <br /> • Incorporate functioning wetland areas. <br /> • Distance between detention inlets and outlets should be maacimized. <br /> • Design wet basins with 3:1 shoreline slopes and native aquatic vegetation. <br /> 3. Require detention on a11 new development for commercial and industrial sites and residential <br /> dwellings of more than one residence per two-acre lot. <br /> 4. Design a development so that small rainfall events would be collected from impervious surfaces <br /> (roofs, driveway, roads, sidew>alks, etc)and preveirted from entering directly irno storm sewers or <br /> road ditches. <br /> Incorporate Better Design Strategies for New and Redeveloped Sites <br /> 1. Reduce impervious surfaces with narrower streets, shorter driveways,nanower sidewalks, reduced <br /> parlang space size, shared parking between adjacent user, shared parking between opposite peak <br /> businesses, and permeable paving. <br /> 2. Promote natural drainage with vegetated swales planted with native grass species. <br /> 3. Establish filter strips or buffers. <br /> 4. Maintain open spaces for environmental benefits, wildlife, and recreation. Floodplains, wetlands, <br /> natural areas, or an��open area can serve as open space. <br /> 5. Encourage i�ltration practices such as infiltration trenches and basins. <br /> 6. Install filtration and biological treatments (i.e. constructed wetlands) <br /> 7. Manage runoff from road surfaces. <br /> 8. Introduce native trees, shrubs,grasses;and forbs. <br /> Preserve the 100-year Floodplain <br /> 1. Deter all construction or filling in of the FEMA 100-year mapped floodplain. <br /> 2. Discourage the placement of detention basins in the floodplain. <br /> 3. The placement of a detention basin in a flood fringe area should require compensatory storage for 1.5 <br /> times the volume belov�-the base flood elevation occupied by the detention basin. <br /> 4. No reduction in existing floodway surface area. <br /> 5. Deter on-stream detention. <br /> 6. Preserve these areas as open space or natural areas planted with native species. Return floodplain to <br /> original native vegetation. <br /> OS/31/02 g <br />