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Stormwater – Quality Management
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Stormwater – Quality Management

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Stormwater – Quality Management

Stormwater – Quality Management

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    Stormwater – Quality Management Stormwater – Quality Management Presentation Transcript

    • Stormwater Infrastructure for Water Quality Management Wali Memon Wali Memon 1
    • The Urban StormwaterProblem Wali Memon Flow QualityRegulated by RegulatedLocal Agencies Principally by EPA & TNRCC Receiving Water 2
    • Increasing ImperviousnessIncreases Runoff Wali Memon Flow Rate 3 Return Period, yrs
    • Stormflow Impacts• 100 year peak flow increases 2 X• 15 year peak flow increases 3 X Wali Memon• 2 year peak flow increases 57 X (Denver)• 2-yr peak flow occurs • 3 X per year (residential development) • 6 X per year (commercial development) 4
    • The STORM Model(Storage Treatment Overflow Runoff Model) Precipitation Wali Memon Wet-Weather Runoff Storage Q=CIA Treatment Overflow 5
    • Typical Capture Curves The Design Storm 100 Percent Capture of Annual Runoff 90 Wali Memon 50% Impervious 50 100% Impervious 6 0.5 20 0 Treatment Volume Required, inches 1.0
    • So What’s the Problem• BMPs target the control of the quality of runoff• Conventional drainage facilities control downstream flooding• Neither of these activities has as its objective protection of the aquatic environment - If it occurs, it is incidental Wali Memon 7
    • Stormwater Mgmt MustAddress the Entire FlowFrequency Curve Wali Memon Flow Rate Frequency Curve with Flood & Water Quality Controls 8 Return Period, yrs
    • The Fact Is: Simply reducing pollutants in the runoff to Wali Memon theMaximum Extent Practicable will probablynot result in significant improvement to theecological condition of the receiving waters 9 Flow management is also required
    • Urban Runoff Hydrology The Design Storm Small storms 85 percent of the storms in east Texas account for Wali Memon are less than 1 inch most of the of rainfall runoff and are affected most 85 percent of the storms in west Texas by urbanization. are less than 0.65 inches 10
    • Maximized Water QualityCapture Volume The Design Storm Wali Memon Po= a • C • PA where: Po = Maximized Water Quality Capture Volume (in.) a = Capture Volume Coefficient C = Watershed Runoff Coefficient 11 PA= Mean Storm Precipitation Volume (in.)
    • Maximized Volume for Texas Po= a • C • PA a = 1.3 - 1.6 for 85% capture of annual runoff PA = 0.6 inches in east Texas (wet) Wali Memon = 0.4 inches in west Texas (dry) Po (wet) = 0.12 - 0.14 inches (residential, C=0.15) = 0.70 - 0.86 inches (commercial, C=0.9) Po (dry) = 0.08 - 0.10 inches (residential, C=0.15) = 0.50 - 0.58 inches (commercial, C=0.9) 12 The Design Storm
    • The Stormwater TreatmentTrain Pollution Prevention • Public Education • Spill Prevention Wali Memon • Used Oil Recycling • Lawn Chemical Mgmt Source Controls • Filter Strips • Swales • Modular Pavement • Infiltration Trenches Treatment Controls • Extended Detention 13 • Retention Ponds • Wetlands
    • Design of Source Controls Wali Memon 14
    • Minimize Directly ConnectedImpervious Area • Drain Hard Lot Surfaces onto Pervious Wali Memon Areas •Use Modular Pavement where Feasible •Drains Streets to 15 Swales
    • Lot/Site Drainage Wali Memon Depressed Grassed Modular Pavement Area Grassed Parking Area 16 Reinforced with Geotextile Fabric
    • Lot/Site Drainage Percolation Trench Wali Memon 17
    • Basic Design CriteriaPercolation Trench• Seasonal High groundwater or bedrock more than 4 ft below trench bottom• Do not locate in fill material or recompacted soils Wali Memon• Soil should be type A or B with minimum hydraulic conductivity of 6.5 x 105 ft/sec• Po based on lot size and %I 18
    • Use Swales for Road andParking Lot Drainage Wali Memon 19
    • Design Criteria Swales • Provide 1-2% slope • Max V < 1 ft/sec • Max bottom width, 8 ft Wali Memon • Min bottom width, 2 ft• Minimum length 100 ft• Maximum water height for maximized storm than 1/2 the height of standing vegetation• Po sized for road runoff plus the portion of 20 maximized storm not captured on building site
    • Infiltration Basins Wali Memon 21
    • Design CriteriaInfiltration Basins• Seasonal groundwater or bedrock > 4 ft below basin bottom• Do not locate on fill or compacted soils• Soil must be type A or B with saturated surface infiltration rate Wali Memon > 0.3 in/hr• Size to drain Po in 12 hour• Use point system in book for rating suitability of a site 22
    • Design of Treatment Controls Wali Memon 23
    • Extended Detention Wali Memon 24
    • Extended DetentionDesign Criteria• Size to detain Po for 12 to 24 hours, then add 20% Wali Memon for sediment storage• Use two stage design (empty less than 50% of volume in first 1/3 of detention time• Sediment forebay recommended• Clogging outlets are most common failure 25• Emergency spillway• Sideslopes 1:4
    • Extended Detention (cont) Wali Memon 26
    • Detention with Filtration Wali Memon 27
    • Detention with FiltrationClassic Application Wali Memon 28
    • Detention with Filtration Design Criteria • Capture Po or 1/2 inch of runoff from impervious area Wali Memon • 24 - 40 hour drawdown time • Minimum sand bed = 18 inches • Seal bottom of filter chamber •Underdrain the sand filter• Provide smooth flow transition from presedi- mentation chamber to filter chamber 29
    • Retention Wali Memon 30
    • Retention - Design Criteria • Design by one of two methods - Solids-settling theory - Lake eutrophication theory Wali Memon • Both facilities are larger than an extended detention basin for the same drainage area • For biochemical design, size to hold runoff from wettest two weeks for 14 days • Design as regional facilities 31 as landscape amenity
    • Constructed Wetland Wali Memon 32
    • Constructed WetlandDesign Criteria • Use same guidelines as biological retention, but Wali Memon detention time is 14 days during wettest month • Open water is less that 50% of total facility surface area • Use a wetland biologist for developing planting program 33
    • Summary• Design for the small storm• Minimize Directly Connected Wali Memon Impervious Area• Use the treatment train concept• Design outlet controls as multi- stage to reproduce natural flow 34 frequency curve
    • Questions! Wali Memon 35