Green Stormwater Infrastructure for Flood Risk Reduction

June 2016

Presented by:

Kari Mackenbach, CFM

ms consultants

Lynn Mayo, PE, CFM

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

Background

Natural water cycle: Pre-development

Natural water cycle: Post-development

• Increased

imperviousness

increases flows

• Decreased water

quality

• Increased erosion

and sediment in

streams

DistributedStormwater Features

Traditional RegionalTechnique

Integrated Stormwater Controls

Distributed stormwater controls close to runoff sources

Is this green infrastructure?

Green Infrastructure Technology Types

Why are

consistent terms

important?

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

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.

Can green stormwater

infrastructure really

reduce flooding?

How is green infrastructure and flooding connected?

Seeing the

significance of the

hydrologic impacts

of urbanization

over time

Street

In a 1”

rainfall

Potential

Runoff:

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

Non-urban green infrastructure

18Green Stormwater Infrastructure for Flood Risk Reduction

New development

Non-urban green infrastructure

• Land Preservation

• Wetland Preservation/Creation

• Floodplain and Stream Restoration (includes set-

back levees)

Non-urban green infrastructure success story

Charles River – USACE acquired 8,000 acres wetlands for

flood control for $9M

– Average Annual flood damage reduction

Urban green stormwater infrastructure

New development

Urban green infrastructure (examples)

• Green roof

• Pervious pavers or pavement

• Rain garden or bioswales

• Infiltration trench

Green stormwater infrastructure used

effectively for flood risk reduction

City of Columbus,

Blueprint Columbus

Green Infrastructure

Strategy

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

University of

Louisville Belknap

Campus

Copenhagen,

Denmark Climate

Resiliency and Flood

Mitigation Strategy

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 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

New development

To be effective flood risk

reduction, need to:

– Change land use to

impact curve number

(i.e., reduce runoff)

– Have available storage

at time of peak flow

Rainfall Hyetograph

Inch r

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

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

New development or redevelopment

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

Existing development

Existing Development Green Stormwater

Infrastructure

Urban GSI Limitations:

– Limited impact for

downstream large

watershed

– Limited impact on large

flood events

Urban GSI Opportunities:

– Opportunities for localized

flooding

Typically limited land available to install green infrastructure

– Opportunities for small

flood events

May affectNot going to affect

Good News: Most flood reduction benefits come

from addressing smaller, frequent events.

May affectNot going to affect

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

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

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

Average Annualized Loss

Average Annualized Loss = estimated long-term weighted average value

of losses to a property in any single year

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)

Annualized

(& / yr)

$40 M $17 M $10 M $10 M $3 M $80 M

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

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

Next steps and comments on ASFPM Policy

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%

Green Stormwater Infrastructure for Flood Risk Reduction

Documents

Montour Falls Flood Damage Reduction Project

Mackay Region Flood and Stormwater Management Strategy · Flood risk refers to (and is a measure of) the likelihood and consequence of the hazard eventuating. Flood and stormwater

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KYOGLE COUNCIL DRAFT OPERATIONAL PLAN DELIVERY …€¦ · Stormwater and Flood Special Rate: In 2015/16 Council changed the way it generates revenue for Stormwater and Flood Management

Duluth Residential Stormwater Reduction Demonstration ......Project title: Duluth Residential Stormwater Reduction Demonstration Project for Lake Superior Tributaries Organization

Amboy Flood Damage Reduction Project

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TUSCARAWAS COUNTY FLOOD DAMAGE REDUCTION REGULATIONS

Flood Damage Reduction Segment / System Inspection Report · Flood Damage Reduction Segment / System . Inspection Report. ... Alfred Zarnoski, P.E.; Joseph Reed; ... Flood Damage

Flood Damage Reduction Making Stormwater Management Systems Reduce Flood Damages

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SAN FRANCISCO STORMWATER FLOOD MANAGEMENT …...SAN FRANCISCO STORMWATER & FLOOD MANAGEMENT PRIORITY PROJECTS Proposition 1E Application Attachment 7 Economic Analysis – Flood Damage

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Flood Damage Reduction Segment / System Inspection … more flood damage reduction systems which ... maintained by a single entity. A flood damage reduction ... Note that an Unacceptable

Chapter E2 | Stormwater and Flood Risk Management

Involving homeowners in urban flood reduction

MMDA Flood Reduction Measures 2

Flood Damage Reduction Segment / System Inspection Report · Flood Damage Reduction Segment / System . Inspection Report. ... Alfred Zarnoski, P.E. ; Joseph Reed . ... Flood Damage

Wetland, An Alternative for Flood and Stormwater Control