Major Topics to Address
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Sizing Stormwater Control Facilities Sizing Stormwater Control Facilities to to Address Stream-Bank Erosion Control Address Stream-Bank Erosion Control Anthony M. Dubin, PE Brown and Caldwell [email protected]
description
Major Topics to Address. Why Hydrograph Modification Management is important How Low Impact Development controls work Describing the technical analysis that generated the set of pre-sized IMPs. Effects of Urbanization. - PowerPoint PPT Presentation
Transcript of Major Topics to Address
Sizing Stormwater Control Facilities to Sizing Stormwater Control Facilities to
Address Stream-Bank Erosion Control Address Stream-Bank Erosion Control
Sizing Stormwater Control Facilities to Sizing Stormwater Control Facilities to
Address Stream-Bank Erosion Control Address Stream-Bank Erosion Control
Anthony M. Dubin, PEBrown and [email protected]
Anthony M. Dubin, PEBrown and [email protected]
Major Topics to AddressMajor Topics to AddressMajor Topics to AddressMajor Topics to Address
1. Why Hydrograph Modification Management is important
2. How Low Impact Development controls work
3. Describing the technical analysis that generated the set of pre-sized IMPs
Effects of UrbanizationEffects of UrbanizationEffects of UrbanizationEffects of Urbanization
• Impervious surfaces produce higher runoff rates, volume and duration of large flows
Effects within the WatershedEffects within the WatershedEffects within the WatershedEffects within the Watershed
• Urbanization alters the watershed• Channels respond with incision and/or
armoring
Continuous Hydrologic Modeling Continuous Hydrologic Modeling Examines Full Range of Local Examines Full Range of Local ConditionsConditions
Continuous Hydrologic Modeling Continuous Hydrologic Modeling Examines Full Range of Local Examines Full Range of Local ConditionsConditions
Sizing to one ‘design storm’ is not enough
Peak Flow FrequencyPeak Flow Frequency(Partial Duration Statistics)(Partial Duration Statistics) Peak Flow FrequencyPeak Flow Frequency(Partial Duration Statistics)(Partial Duration Statistics)
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0.20
0.40
0.60
0.80
1.00
1.20
0 1 2 3 4 5 6 7 8 9 10
Recurrence Interval (years)
Pea
k F
low
(cf
s)
Impervious
Pre-Project Site
0.5Q2
Identify all HSPF storms in record and rank
Flow DurationsFlow DurationsFlow DurationsFlow Durations
0.00
0.10
0.20
0.30
0.40
0.50
0.60
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0.80
0.90
1.00
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
% Time Exceeded
Flo
w (
cfs
)
Impervious
Pre-Project SiteQ10
0.1Q2
Rank hourly outputs from HSPF model
Example IMP: In-Ground PlanterExample IMP: In-Ground PlanterExample IMP: In-Ground PlanterExample IMP: In-Ground Planter
18-in sandy loam
Peak Flow Matching ExamplePeak Flow Matching ExamplePeak Flow Matching ExamplePeak Flow Matching Example
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 1 2 3 4 5 6 7 8 9 10
Recurrence Interval (years)
Pea
k F
low
(cf
s)
ImperviousMitigated Post-Project SitePre-Project Site0.5Q2
IMP Reduces Impervious Runoff to Less Than Pre-Project Levels
Duration Matching ExampleDuration Matching ExampleDuration Matching ExampleDuration Matching Example
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0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
% Time Exceeded
Flo
w (
cfs
)
ImperviousMitigated Post-Project SitePre-Project SiteQ100.1Q2
IMP Reduces Impervious Runoff to Less Than Pre-Project Levels
BMP Sizing Factor SummaryBMP Sizing Factor SummaryBMP Sizing Factor SummaryBMP Sizing Factor Summary
IMP Sizing Factors
In-Ground Planter
Group A: 0.08Group B: 0.11Group C: 0.06Group D: 0.05
Flow-Through Planter
Group C: 0.06Group D: 0.05
Vegetated/Grassy Swale
Group A: 0.10 to 0.14
Group B: 0.14 to 0.21
Group C: 0.10 to 0.15
Group D: 0.07 to 0.12
Bioretention Basin
Group A: 0.13Group B: 0.15Group C: 0.08Group D: 0.06
IMP Sizing Factors
Dry Well Group A: 0.05 to 0.06Group B: 0.06 to 0.09
Infiltration Trench
Group A: 0.05 to 0.06Group B: 0.07 to 0.10
Infiltration Basin
Group A: 0.05 to 0.10Group B: 0.06 to 0.16
Infiltration Only:Under-Drain or Infiltration:
Adjusting IMP Sizing to Account Adjusting IMP Sizing to Account for Rainfall Variability for Rainfall Variability Adjusting IMP Sizing to Account Adjusting IMP Sizing to Account for Rainfall Variability for Rainfall Variability
Group A, y = 0.0020x + 0.08Group B, y = -0.0005x + 0.11Group C, y = -0.0022x + 0.06Group D, y = -0.0022x + 0.05
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0.02
0.04
0.06
0.08
0.10
0.12
0.14
-14 -12 -10 -8 -6 -4 -2 0 2 4 6
Mean Annual Rainfall (MAP) Relative to Martinez Gauge (in)
Siz
ing
Fac
tor
Group A soils
Group B soils
Group C soils
Group D soils
Sizing Conclusions for Sizing Conclusions for ImplementationImplementationSizing Conclusions for Sizing Conclusions for ImplementationImplementation
• IMPs in Group D soil sites are generally smaller than Group A soil BMPs
• Steep side walls produce smaller sizing factors
• Sizing factor may be particularly important for on-site BMPs
• Swales and Bioretention basin footprint may be less important if BMPs fit into otherwise undeveloped space
Questions?Questions?Questions?Questions?
Contra Costa Approach to Contra Costa Approach to Hydrograph ModificationHydrograph ModificationContra Costa Approach to Contra Costa Approach to Hydrograph ModificationHydrograph Modification
• Encourage LID to control stormwater flows
• HMP is technically rigorous and easy to apply
• Assumes need to match pre-project condition
BMP GalleryBMP GalleryBMP GalleryBMP Gallery
BMP GalleryBMP GalleryBMP GalleryBMP Gallery
Instructions for Computing Local Instructions for Computing Local Sizing Factors Sizing Factors Instructions for Computing Local Instructions for Computing Local Sizing Factors Sizing Factors
1. Describe each DMA on the project site, including area, soil type, post-project surface type
2. For DMA's draining to IMPs, select an IMP and configuration (e.g. swale width, dry well depth)
3. Pick the appropriate sizing factor from the summary sizing factor table (see handout)
4. Compute the rainfall adjustment using the regression equations (see handout)
5. Local sizing factor = Sizing Factor x RainAdj
