Adapting Stormwater Management to Climate Change
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Transcript of Adapting Stormwater Management to Climate Change
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Adapting Stormwater Management to Climate
Change
Ken PotterDepartment of Civil & Environmental
EngineeringUniversity of Wisconsin-Madison
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SUMMARY
• Urbanization has adverse hydrologic impacts, including increased flooding, diminished water quality, and decreased baseflow.
• Conventional and emerging storm-water management practices are based on historical climate.
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SUMMARY
• We may very well not know how local climates will change until after the fact.
• A potentially effective strategy is to design conservatively to hedge against possible increases in storm intensities.
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SUMMARY
• Other potential strategies are to
– Improve performance of existing systems based on monitoring and modeling;
– Introduce capacity for real-time management.
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HYDROLOGICAL IMPACTS OF URBANIZATIONIncreased Rate of Runoff
Introduction of Impervious
Surfaces
“Improvement” of Drainage
System
Increased Amount of Runoff
Lowered Ground-
Water Levels
Increased Flooding
(Streams and Lakes)
Degraded WaterQuality
DecreasedBaseflowCompaction of
Pervious SurfacesGroundwater
Pumping
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1995 RUNOFFGARFOOT CREEK
Garfoot
Runoff(inches)
JanuaryApril July
October
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1995 RUNOFFGARFOOT CREEK AND
SPRING HARBOR STORMSEWER
GarfootSpring Harbor
Runoff(inches)
JanuaryApril July
October
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STORMWATER MANAGEMENT PRACTICES
• Conveyance, through storm sewers and engineered channels
• Storage, to prevent increases in runoff peaks and improve water quality
• Infiltration, to decrease runoff volumes and increase ground water recharge
• Filtration, to improve water quality
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CLIMATE AND DESIGN
• Stormwater management design is commonly based on design storms, such as the 10-year, 24-hour storm.
• There is general belief that the magnitude of these storms will increase a a result of climate change.
• How should stormwater managers proceed?
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POTENTIAL STRATEGIES FOR ADAPTING TO CLIMATE
CHANGE
• Design conservatively.
• Improve performance of existing systems based on monitoring and modeling.
• Introduce capacity for real-time management.
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CONSERVATIVE DESIGN
Requires a logical basis.• Regulate to the 100-year event.• Reduce consequences of events > design.• Use regularly updated rainfall statistics.• Use lowest pre-development CNs that can be
justified.• Aggressively infiltrate, but do not credit
storage towards peak requirement.
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100-year Flood Routed through a 10-year Detention Pond
Inflow (cfs)Outflow (cfs)
TIME (hrs)
Pre-Development Q100
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CONSERVATIVE DESIGN
Requires a logical basis.• Regulate to the 100-year event.• Reduce consequences of events > design.• Use regularly updated rainfall statistics.• Use lowest pre-development CNs that can be
justified.• Aggressively infiltrate, but do not credit
storage towards peak requirement.
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CONSERVATIVE DESIGN
Requires a logical basis.• Regulate to the 100-year event.• Reduce consequences of events > design.• Use regularly updated rainfall statistics.• Use lowest pre-development CNs that can be
justified.• Aggressively infiltrate, but do not credit
storage towards peak requirement.
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CONSERVATIVE DESIGN
Requires a logical basis.• Regulate to the 100-year event.• Reduce consequences of events > design.• Use regularly updated rainfall statistics.• Use lowest pre-development CNs that can
be justified.• Aggressively infiltrate, but do not credit
storage towards peak requirement.
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CONSERVATIVE DESIGN
Requires a logical basis.• Regulate to the 100-year event.• Reduce consequences of events > design.• Use regularly updated rainfall statistics.• Use lowest pre-development CNs that can be
justified.• Aggressively infiltrate, but do not credit
storage towards peak requirement.
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HYPOTHETICAL INFILTRATION CASE STUDY
• 160-acre development• 50% impervious• Pre- and post-development pervious CN
– Case 1: 70 (B soils)– Case 1: 79 (C soils)
• Present climate: Midwestern Climate Center Bulletin 71
• Future climate: 15% increase in design rainfalls
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PROCEDURE
• Designed a pond and outlet structure to control 100-year event.
• Routed a 100-year event based on +15% rainfall.
• Modified runoff assuming infiltration practices that controlled 2-year event (8-in. depression; 12-in. subsurface storage; 6 in./hr. infiltration rate for engineered layers).
• Repeated routing with +15% rainfall.
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RESULTS: CN = 70
Q100 (cfs)
Current P Pre-dev. 73
Post-dev. 411
Post dev. w/detention 73
1.15 P Post-dev. 489 (+19%)
Post dev. w/detention 170 (+100%)
Post dev. w/detention & infiltration 74
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RESULTS: CN = 79
Q100 (cfs)
Current P Pre-dev. 94
Post-dev. 452
Post dev. w/detention 94
1.15 P Post-dev. 528 (+17%)
Post dev. w/detention 188 (+100%)
Post dev. w/detention & infiltration 113 (+20%)
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RESULTS: CN = 79
Bioretention Area
(% of total area) Q100 (cfs)
7.0% 113 (+20%)
8.0% 104 (+11%)
9.0% 95 (+1%)
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POTENTIAL STRATEGIES FOR ADAPTING TO CLIMATE
CHANGE
• Design conservatively.
• Improve performance of existing systems based on monitoring and modeling.
• Introduce capacity for real-time management.
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IMPROVING SYSTEM PERFORMANCE
• Monitor individual storages to verify assumed– Storage-outflow characteristics;– Hydrologic parameters.
• Model system using continuous simulation to identify ways to improves system performance.
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POTENTIAL STRATEGIES FOR ADAPTING TO CLIMATE
CHANGE
• Design conservatively.
• Improve performance of existing systems based on monitoring and modeling.
• Introduce capacity for real-time management.
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400
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100 yr. Inflow with 1.15 PDetention and Diversion
Total Inflow (c (cfs)Outflow with Diversion (cfs)Outflow w/o Diversion (cfs)
TIME (hrs)
Pre-Development Q100
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SUMMARY AND CONCLUSIONS
• The local affects of climate change on stormwater are highly uncertain.
• There are a number of hedges against increases in storm intensities that can be easily justified.
• Aggressive use of infiltration practices is a promising example.
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SUMMARY AND CONCLUSIONS
• Another promising strategy is to improve system performance using monitoring and modeling.
• Based on a preliminary analysis, it does not appear the real-time management will be effective.