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

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Design Example – Sizing of Water Quality Combination Basin in Sacramento CountyWatershed and Basin DataWatershed Area = 210 acresWatershed Imperviousness = 39%Basin Type = Combination Water Quality Basin also used for Flood Control1. Calculate the Water Quality Storage Volume (WQV)For a Water Quality Detention Basin, the WQV is calculated from the methodology inAppendix E using a 48-hour drawdown time.• From Figure E-3 the unit storage is determined to be 0.29 inches• WQV = 0.29 (in) x 210 (acre) ÷ 12 = 5.1 acre-feet• Permanent Pool Volume = 0.625 x WQV = 3.2 acre-feet• Wet Weather Pool Volume = 0.500 x WQV = 2.5 acre-feet2. Size the Sediment ForebayThe sediment forebay size should be 5 to 10 percent of the maximum total design volume.• Minimum Sediment Forebay Volume = (3.2 + 2.5) x 0.05 = 0.29 acre-feet minimum3. Design the BasinDetention basin layouts will vary significantly based on site specific conditions. For thisexample, it is assumed that the permanent pool will have an average depth of 4 feet and alength to width ratio of 3 to 1. Based on these requirements, the bottom dimensions of thebasin will be 300’ x 100’ (L x W) and the side slopes will be 3 to 1. The hypothetical basinwill have the following elevation storage relationship.Elev. (ft) Depth (ft) Area (ac) Storage (ac-ft) Notes100.0 0.0 0.7 0.0101.0 1.0 0.7 0.7102.0 2.0 0.8 1.5103.0 3.0 0.9 2.3104.0 4.0 0.9 3.2 Permanent Pool Elevation105.0 5.0 1.0 4.2106.0 6.0 1.0 5.2106.5 6.5 1.1 5.7 Wet Weather Pool Elevation107.0 7.0 2.7 6.7
4. Design the OutletThe outlet should be sized to release the 75 percent of the wet weather pool volume in aminimum of 24 hours and release the remaining volume over an additional 16 to 24 hours. Forthis example the outlet is assumed to be a stand pipe with the top of the pipe at the wetweather pool elevation and a single orifice placed just above the permanent pool elevation.The orifice can be sized using the orifice equation and a simple spreadsheet calculation suchas the one shown on Exhibit 1. As shown on Exhibit 1, an orifice with an area of 23.8 squareinches will produce the desired drain time. The size of the stand pipe is based on the capacityrequired to pass the appropriate design storms.5. Flood Control DesignWater quality basins can often be used to provide flood control benefits. The storage volumeabove the water quality pool can act to reduce peak flood flows downstream of the basin. Therequired storage volume and storm outlet size are typically determined by routing floodhydrographs through the detention basin using a computer program such as SacCalc, HEC-1,HEC-RAS, or other equivalent program. For this example, it is assumed that flood routingwas performed and 6.8 acre-feet of storage is required to attenuate flood flows to the desireddownstream level. To meet this storage requirement, the basin is widened to create a floodcontrol bench just above the maximum water quality pool as shown in the following crosssection.Bank Elev. 110’Flood Control Pool(6.8 ac-ft)Wet Weather Pool(2.5 ac-ft)Permanent Pool (3.2 ac-ft)Elev. 109’Elev. 106.5’Elev. 104’100’200’
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Stormwater Quality Design Manualfor
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Table of contentsOutdoor Work Areas
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Table of contentsSF-1.SF-2.SF-3.SF-
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Other Development Community Reviewe
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1 IntroductionPurposeThis Stormwate
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IntroductionIn July 2003, the permi
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IntroductionFor redevelopment proje
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Introduction• The Appendices prov
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2 An Integrated Approach toEffectiv
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Integrated ApproachIt is also helpf
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Integrated ApproachPut landscaping
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Integrated Approachfactors will be
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Chapter 3Figure 3-1. Process for Ad
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Chapter 3runoff reduction first (ev
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Chapter 3As the name implies (and a
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Chapter 3Step 9: Establish Long Ter
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Chapter 4Source Control Fact Sheets
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Source Control Measure Fact SheetSt
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Source Control Measure Fact SheetFu
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5 Runoff Reduction Control Measures
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Runoff Reduction Control MeasuresDe
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Runoff Reduction Control Measures
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Chapter 6• What are pollutants of
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Chapter 6For projects using any of
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Runoff Treatment Control Measure Fa
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Design Data Summary SheetConstructe
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Technical RequirementsInfiltration
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Technical RequirementsSand FilterSa
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Technical RequirementsVegetated Swa
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Glossaryexposure of construction ma
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GlossaryLow Impact Development (LID
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GlossaryRegional Stormwater Quality
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Appendix ASubmittal RequirementsThe
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Sacramento County Supplemental Appl
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Example Post Construction Stormwate
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Typically maintenance agreements an
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Example Maintenance Covenant(Sacram
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Device in accordance with the maint
Page 210 and 211: [attach]DECLARANT’S ACKNOWLEGEMEN
Page 212 and 213: Recorded at the request of:CITY OF
Page 214 and 215: 9. The obligations herein undertake
Page 216 and 217: EXHIBIT B[Map/Illustration]
Page 218 and 219: City of FolsomThe City of Folsom ow
Page 220 and 221: Appendix D-1: Residential Sites: Ru
Page 222: Form D-1d: Alternative Driveway Des
Page 225 and 226: Form D-2a: Disconnected Pavement Wo
Page 228 and 229: Appendix D-3Runoff Reduction Credit
Page 230 and 231: These tables refer to runoff reduct
Page 232 and 233: Mature TreeShape Canopy (dia.) Heig
Page 234 and 235: Appendix D4LID Credits Background R
Page 236 and 237: unoff from the driveway by 60% whil
Page 238 and 239: The designer must determine how man
Page 240 and 241: Or the ASCE-WEF method (Sacramento)
Page 242 and 243: Table 3 - Multipliers Based on Rati
Page 244 and 245: Using the Effective Area Managed in
Page 246 and 247: SMRC, The Stormwater Manager’s Re
Page 248 and 249: Flow-based control measure design s
Page 250 and 251: 4. Apply the Rational Formula to ca
Page 252 and 253: 5. Enter the capture curve selected
Page 254 and 255: 1.201.000.80STORAGE (in)0.600.4024-
Page 256 and 257: 1.201.000.80STORAGE (in)0.600.4048
Page 258 and 259: Subject: VEGETATED SWALE EXAMPLEPLA
Page 260: PART II:Routing Excess Runoff throu
Page 265 and 266: Exhibit 1Water Quality Orifice Outl
Page 267 and 268: 3. Calculate Planter Surface Area A
Page 269 and 270: • Bottom slopes of 0.01 to 0.05%
Page 271: Appendix HDrainage Design and Storm
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