Green Stormwater Infrastructure for Flood Risk Reduction
Transcript of Green Stormwater Infrastructure for Flood Risk Reduction
June 2016
Presented by:
Kari Mackenbach, CFM
ms consultants
Lynn Mayo, PE, CFM
AECOM
Green Stormwater
Infrastructure for
Flood Risk Reduction
Topics
1. Proposed ASFPM Policy Paper
2. Background
– Why is the issue important
3. Policy Paper
– Proposed terminology
– Use of green infrastructure for flood mitigation
– Calculating benefits of green infrastructure for flood mitigation
4. Next steps and comments on ASFPM Policy Paper
Green Stormwater Infrastructure for Flood Risk Reduction 2
Proposed ASFPM
Policy Paper
Consistent use of terms
Effectiveness of Green
Infrastructure for flood risk
reduction
Green Stormwater Infrastructure for Flood Risk Reduction 3
Background
Green Stormwater Infrastructure for Flood Risk Reduction 4
Natural water cycle: Pre-development
Green Stormwater Infrastructure for Flood Risk Reduction 5
Natural water cycle: Post-development
• Increased
imperviousness
increases flows
• Decreased water
quality
• Increased erosion
and sediment in
streams
Green Stormwater Infrastructure for Flood Risk Reduction 6
DistributedStormwater Features
Traditional RegionalTechnique
Integrated Stormwater Controls
Distributed stormwater controls close to runoff sources
Green Stormwater Infrastructure for Flood Risk Reduction 7
Is this green infrastructure?
Green Stormwater Infrastructure for Flood Risk Reduction 8
Is this green infrastructure?
Green Stormwater Infrastructure for Flood Risk Reduction 9
Green Infrastructure Technology Types
Why are
consistent terms
important?
Green Stormwater Infrastructure for Flood Risk Reduction 11
Definitions of “green infrastructure”
American Planning Association (first used term in 1994)*:
– Interconnected system of natural areas and open space that:
• conserves ecosystem values,
• helps sustain clean air and water, and
• provides benefits to people and wildlife
EPA Definition (first used term in 2007)*:
– Preserving and recreating natural landscape features
– Minimizing effective imperviousness to create functional and
appealing site drainage
– Treating stormwater as a resource rather than a waste product
• from Karen Firehock, 2010
Green Stormwater Infrastructure for Flood Risk Reduction 12
Definitions of “green infrastructure”
US Army Corps of Engineers:
– Integration of natural systems and processes, or engineered
systems that mimic natural systems and processes, into investment
in resilient infrastructure
ASFPM:
– No Adverse Impact Toolkit… Green infrastructure is a proactive,
systematic, multifunctional model that views open space on a large
scale and better integrates open/green space planning with other
efforts to manage growth and development. It essentially uses
stormwater storage areas, water conveyance areas and other
natural flooded areas as part of the community infrastructure for
stormwater and flood damage reduction, as well as for parks, trails
and other recreation areas.
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Can green stormwater
infrastructure really
reduce flooding?
Green Stormwater Infrastructure for Flood Risk Reduction 14
How is green infrastructure and flooding connected?
Seeing the
significance of the
hydrologic impacts
of urbanization
over time
Green Stormwater Infrastructure for Flood Risk Reduction 15
Street
In a 1”
rainfall
Potential
Runoff:
7,040
gallons
2,500 s.f.
“impervious” x 1” rain =
1,559 gallons
of runoffStormdrain
1,500 s.f. house (& patio) x 1” rain =
935 gallons of runoff
+ “Green Concrete” Compacted Lawn
8,390 s.f. “impervious” x 1” rain (if infiltrates first ¼” of rain)
= 3,923 gallons of runoff
1,000 s.f.
driveway x 1”
rain = 624
gallons of
runoff
How is green infrastructure and flooding connected?
Green infrastructure flood risk reduction
potential benefits
Depends on type of GI: • Non-urban green infrastructure
• Urban green stormwater infrastructure
– New development
– Existing development
Green Stormwater Infrastructure for Flood Risk Reduction 17
Non-urban green infrastructure
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New development
Non-urban green infrastructure
• Land Preservation
• Wetland Preservation/Creation
• Floodplain and Stream Restoration (includes set-
back levees)
Green Stormwater Infrastructure for Flood Risk Reduction 19
Non-urban green infrastructure success story
Charles River – USACE acquired 8,000 acres wetlands for
flood control for $9M
– Average Annual flood damage reduction
$17M
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Urban green stormwater infrastructure
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New development
Urban green infrastructure (examples)
• Green roof
• Pervious pavers or pavement
Green Stormwater Infrastructure for Flood Risk Reduction 22
• Rain garden or bioswales
• Infiltration trench
Green stormwater infrastructure used
effectively for flood risk reduction
City of Columbus,
Blueprint Columbus
Green Infrastructure
Strategy
23Green Stormwater Infrastructure for Flood Risk Reduction
Urban green stormwater infrastructure
success story
Cuyahoga Falls
green infrastructure
mitigation park project
– FEMA grant to acquire 4 homes
– Space converted into green infrastructure
– Reduced flooding for remaining homes
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Green stormwater infrastructure used
effectively for flood risk reduction
University of
Louisville Belknap
Campus
25Green Stormwater Infrastructure for Flood Risk Reduction
Green stormwater infrastructure used
effectively for flood risk reduction
Copenhagen,
Denmark Climate
Resiliency and Flood
Mitigation Strategy
26Green Stormwater Infrastructure for Flood Risk Reduction
On July 2, 2011, a cloud burst inundated Copenhagen
with 6 inches of rain in less than three hours, flooding
cellars, streets, and key roads. ($1.04 billion) in damage.
Proposed ASFPM
Policy Paper
Consistent use of terms
Effectiveness of Green
Infrastructure for flood risk
reduction
Green Stormwater Infrastructure for Flood Risk Reduction 27
Green infrastructure flood risk reduction
potential benefits
Depends on type of GI: • Non-urban green infrastructure
• Urban green stormwater infrastructure
– New development or redevelopment
– Existing development
Green Stormwater Infrastructure for Flood Risk Reduction 28
Urban green stormwater infrastructure
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New development
Urban green stormwater infrastructure
To be effective flood risk
reduction, need to:
– Change land use to
impact curve number
(i.e., reduce runoff)
or
– Have available storage
at time of peak flow
Rainfall Hyetograph
Inch r
ain
fall
Green Stormwater Infrastructure for Flood Risk Reduction 30
Urban green stormwater infrastructure
New
Development
GI can change land use to
impact curve number and
reduce flowa
GI can add storage so water
detained at time of peak flow a
Green Stormwater Infrastructure for Flood Risk Reduction 31
Urban green stormwater infrastructure
New
Development
Existing
Development
GI can change land use to
impact curve number and
reduce flowa s
GI can add storage so water
detained at time of peak flow a s
Green Stormwater Infrastructure for Flood Risk Reduction 32
Urban green stormwater infrastructure
New development or redevelopment
Green Stormwater Infrastructure for Flood Risk Reduction 33
EPA study on GI for flood loss avoidance
(for new development or redevelopment)
• Assumed GI retained:
– Redevelopment: Approximately 0.7–1.3 inch rainfall
– New development: Approximately 0.9–1.5 inch rainfall
• Evaluated 20 HEC8 watersheds with and without GI retention out
to year 2040
• Benefits: Flood losses without GI / flood losses with GI
• Losses Avoided- HAZUS modeling results
– Present value 2020 to 2040 = $0.4 to $1 billion
– Average over 20 years = $30 to $65 million per year
Source: EPA, Flood Loss Avoidance Benefits of Green Infrastructure for Stormwater Management, December 2015
Green Stormwater Infrastructure for Flood Risk Reduction 34
Urban green stormwater infrastructure
Existing development
Green Stormwater Infrastructure for Flood Risk Reduction 35
Existing Development Green Stormwater
Infrastructure
Urban GSI Limitations:
– Limited impact for
downstream large
watershed
– Limited impact on large
flood events
Green Stormwater Infrastructure for Flood Risk Reduction 36
Urban GSI Opportunities:
– Opportunities for localized
flooding
Typically limited land available to install green infrastructure
– Opportunities for small
flood events
Urban green stormwater infrastructure
May affectNot going to affect
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Urban green stormwater infrastructure
Good News: Most flood reduction benefits come
from addressing smaller, frequent events.
May affectNot going to affect
Green Stormwater Infrastructure for Flood Risk Reduction 38
Example estimated damages from different storm events in Concord, MA
Total expected dollar losses from flooded buildings and contents
10% (10 yr) 4% (25 yr) 2% (50 yr) 1% (100 yr) 0.2% (500 yr)
$593 M $749 M $905 M $1,199 M $1,459 M
Source: Concord, MA, Flood Risk Report
Green Stormwater Infrastructure for Flood Risk Reduction 39
Example estimated damages from different storm events in Concord, MA
Total expected dollar losses from flooded buildings and contents
10% (10 yr) 4% (25 yr) 2% (50 yr) 1% (100 yr) 0.2% (500 yr)
$593 M $749 M $905 M $1,199 M $1,459 M
10% chance have $593M in damage any given year
$593M x 10% = $59M
Source: Concord, MA, Flood Risk Report
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Example estimated damages from different storm events in Concord, MA
Total expected dollar losses from flooded buildings and contents
10% (10 yr) 4% (25 yr) 2% (50 yr) 1% (100 yr) 0.2% (500 yr)
$593 M $749 M $905 M $1,199 M $1,459 M
10% chance have $593M in damage any given year
$593M x 10% = $59M
0.2% chance have $1,459M in damage any given year
$1,459M x 0.2% = $3M
Source: Concord, MA, Flood Risk Report
Green Stormwater Infrastructure for Flood Risk Reduction 41
Average Annualized Loss
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Average Annualized Loss = estimated long-term weighted average value
of losses to a property in any single year
Example estimated damages from different storm events in Concord, MA
Source: Concord, MA, Flood Risk Report
Total expected dollar losses from flooded buildings and contents
10% (10 yr) 4% (25 yr) 2% (50 yr) 1% (100 yr) 0.2% (500 yr)
$593 M $749 M $905 M $1,199 M $1,459 M
Total annualized losses from flooded buildings and contents
10% (10 yr) 4% (25 yr) 2% (50 yr) 1% (100 yr) 0.2% (500 yr)
TOTAL
Annualized
(& / yr)
$40 M $17 M $10 M $10 M $3 M $80 M
Green Stormwater Infrastructure for Flood Risk Reduction 43
Commercial flooding- often most effective
Addressing “nuisance” flooding in commercial areas
– Typically more dense
development
– Loss of function, including
loss of access to area
– Customers stay away
– High content value
– Vehicle detour time and mileage
Potentially significant benefit of reducing
flood elevation by less than a foot
Green Stormwater Infrastructure for Flood Risk Reduction 44
Non-urban green
infrastructure
– Potential flood
benefits for
large events
Urban green stormwater
infrastructure – existing
development
– Potential flood benefits
for small events
– Biggest long-term
benefits are from small
events
Urban green stormwater
infrastructure – new
development
– Potential flood
benefits for large
events
Summary
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Next steps and comments on ASFPM Policy
Paper
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Average Annualized Loss (AAL)
AAL = estimated long-term weighted average value of losses to a
property in any single year in a specified geographic area
AAL = (10% - 4%) * (Loss 10% + Loss 4%) / 2 +
(4% - 2%) * (Loss 4% + Loss 2%) / 2 +
(2% - 1%) * (Loss 2% + Loss 1%) / 2 +
(1% - 0.2%) * (Loss 1% + Loss 0.2%) / 2 +
0.2% * Loss 2%
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