Stormwater Quality Design Manual (May 2007) - City of Sacramento ...

Runoff Treatment Control Measure Fact SheetWater Quality Detention BasinsDesign Criteria: Design using the following criteria:• The gravel media - 1” to 1-1/2” in size. The porosity of the gravel bed is approximately 0.4• The bed depth – d = 2 feet (The depth of media is selected by allowing consideration for bottomsediment buildup and rooting requirements of desired vegetation.)• The design porosity of the gravel bed - ε = 0.3• The effective hydraulic conductivity shall be less than 95,000 ft/day.• Nominal hydraulic detention time through the gravel bed, τ = 2 days.Surface Area = SA = L W = (τ Q) / (d ε) = (2 days)Q/(2 feet)(0.3)(86400 sec/day)where Q= dry weather design flow rate (cfs)Step 8 - Prepare a Landscaping PlanRetain a certified landscape architect or wetland specialist to prepare a landscaping plan that includes:• a planting layout showing what species to plant where• plant sizes (e.g. seed, plug, 1-gallon container, etc.)• planting techniques• plant spacing• soil amendments• hydroseed specifications• Irrigation specifications (which must conform to applicable local regulations)Consider the following when choosing plants:• Do not plant trees at the base of any access ramps, around any inlet, outlet or culvert, or within 5to 10 feet of a concrete structure or channel.• Cluster trees and shrubs when possible to make mowing of basin easier.• Trees may not be allowed on the basin floor (check with local permitting agency).• Use native plants.• Choose plants that are adapted to the site conditions, including the expected degree ofinundation/soil moisture.• Incorporate plants known to improve water quality.• Where possible, specify an array of plant types, including emergent species (in channels/ponds),herbaceous species, and trees and shrubs (along the outer borders). This results in a more naturalsystem and enhances the aesthetic and wildlife value. However, shrubs and trees should not beused for clay-lined permanent ponds or basins.See Tables DB-3 and DB-4 for a list of suitable plants for different degrees of inundation/soil saturation.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007DB-9