12 februari 2010

WB - Roundtable Urban Flood Risk Management

Structural & Nonstructural Solutions Session

17 March 2011

Structural & non-structural response

to urban flood vulnerability

Frans van de Ven and Kees Bons

Preamble

• The world changes

Climate, population, technology, economy

• No solutions, just responses by adaptation measures (AM)

• Structural adaptation measures (SAMs):

Constructed permanent facilities to reduce the damage risk

• Non-structural adaptation measures (NSAMs):

Responses to urban water problems that may not involve fixed or

permanent facilities. Their positive contribution to risk reduction is

most likely through a process of influencing behavior, usually

through building capacity in all stakeholders through active learning

and appropriate and effective engagement between stakeholders

(Taylor and Wong, 2002).

Measures we could take to reduce flood risk

> 185 adaptation measures identified…..

SAMs: Structural (hard) measures (# >100)

Collective: e.g. dikes, drainage systems

Individual: e.g. wet or dry proofing

NSAMs: Non-structural (soft) measures (# > 85)

Collective: e.g. contingency plans, legislation

Individual: e.g. risk consciousness, insurance

… and counting

Adaptation measures

Objective: Reduce vulnerability of urban areas

by

• avoiding damage

• damage reduction

• creating redundancy and adaptability for long term, unexpected change

But what is their effect and effectivity ? (e.g. retention pond)

• In everyday situation

• Under design conditions (T = 10-100 years)

• Under very extreme conditions (T = 500 – >1000 years)

Threshold capacity

Coping capacity

Recovery capacity

Adaptive capacity

recurrence time

Strategy to reduce/manage vulnerability

* Graaf, R. de, N. van de Giesen and F. van de Ven, 2007, Alternative water management

options to reduce vulnerability for climate change in the Netherlands, Natural Hazards nov.

Strengthen four capacities* to reduce vulnerability

Vulnerability reduction approach

First priority:

SAMs to strengthen threshold capacity for fluvial and coastal flooding

e.g. World Bank (2010) Climate risk and Adaptation in Asian Coastal Megacities

Consequences:

• Other capacities and NSAMs get neglected

• Increased vulnerability for other risks e.g. pluvial flooding, drought, land subsidence, heat …

• Lock-in

• Effectivity in very extreme conditions (T>100 yr) is poor

• Adaptability is limited

Vulnerability reduction approach

Conclusion:

• Strengthen all four capacities

• SAMs show limited adaptability

• Most SAMs strengthen threshold & coping capacity

• SAMs require high federal or regional investments

• NSAMs require less, local or individual investments

• NSAMs require study (learning) and regular training

• SAMs can’t do without NSAMs

SAMs can’t do without NSAMs

What would have happened …

• in Holland without effective flood early warning system

• in Indonesia with an effective tsunami warning system

• in New Orleans without an effective evacuation plan

• in Brisbane if their zoning plan had been water resilient

• in Shanghai if land subsidence by groundwater extractions wasn’t stopped

• in HCM City if their coping and recovery capacity for flooding was limited

• In Tokyo without emergency package for 72 hours survival

• If flood victims were unaware of public health risks of water

• In La Paz if authorities prevented building georisk zone

SAMS are only effective if people are aware, prepared, trained

and space use and construction are regulated

(and preparedness, rules and regulations are maintained)

Adaptation measures

Effectivity specs of AMs

• Retention volume

• Flow reduction

• Detention/retention time

• Effectivity in range T=0.1 till T=1000 years

• Effectivity for coastal/fluvial/pluvial/ groundwater flooding,

drought, subsidence, heat

• Counter-effectivity for other extreme conditions

• Effectivity in combination with other AMs

• Damage reduction effect

• Long term adaptability

• Water quality impacts

• Spatial impacts

• Boundary conditions

• Costs

• Implementation / realization

• Maintenance

• Multipurpose functionality / collateral benefits

Effectivity specs of wetlands

• Retention volume X m3 or x mm

• Flow reduction Y m3.s-1 max outflow

• Detention/retention time H min

• Effectivity 100 % for T<10 years; for T>20 only 10 %

• Effectivity for pluvial flooding, drought, heat

• Counter-effective for -

• Effectivity in combination with AMs to reduce damage for T>20 events

• Damage reduction effect avoid/reduce flooding downstream

• Long term adaptability limited

• Water quality impacts positive

• Spatial impacts requires substantial space

• Boundary conditions relatively flat terrain

• Costs

• Realization substantial

• Maintenance average

• Collateral benefits urban landscape; ecological diversity

Effectivity specs of flood risk in land use plan

• Retention volume tbd

• Flow reduction tbd

• Detention/retention time tbd

• Effectivity events in range T=0.1 till T=1000 years

• Effectivity for pluvial/ fluvial flooding, subsidence

• Counter-effective for drought risk (?)

• Effectivity in combination set of AMs is part of plan

• Damage reduction effect avoid/reduce flooding in project area

and downstream

• Long term adaptability medium - high

• Water quality impacts -

• Spatial impacts substantial; zoning and design

• Boundary conditions project area

• Costs

• Realization limited

• Maintenance limited

• Collateral benefits sustainable urban development / retrofit

How to select an appropriate set of AMs?

Three-step approach

1: Complete vulnerability-analysis

2: Select a strategy to reduce vulnerability

3: Select appropriate set of measures

many stakeholders / many stakes

many SAMs and NSAMs

design and negotiation approach

Involved stakeholders

Public

State

Province

Municipality

Water board

….

Private

Home owner / occupant

Real estate developers

Housing associations

Waterworks

Electricity companies

Telecom companies

Insurance companies

Mortgage banks

….

Notions:

• Many AMs require active involvement of private parties

• Different parties/people involved in each phase of (re)development process

Resulting portfolio of AMs

1. Threshold capacity

Waterrobust infrastructure

Enlarged seasonal storage

High floor level vs street level

Floating housing

2. Coping capacity

Major drainage system; adapted street

profile

Wet proofing vulnerable buildings

Warm grass instead cold grasses

4. Adaptive capacity

Temporary houses & buildings

Adaptive management

Water-based spatial planning

Updates water & space policies

3. Recovery capacity

Redundant pumping capacity

Cleaning & drying capacity

Water supply capacity in extremely dry

periods

Measures to strengthen …

Resulting design New Orleans

Dutch Dialogues III, April 2010, www.dutchdialogues.com

Closing

frans.vandeven@deltares.nl

+31 (0)6 5183 5010

• SAMs can’t do without NSAMs

• Numerous alternative responses

• Four capacities to be strengthened

• Effectivity under very extreme conditions

• Many stakeholders: Design- & negotiation approach

Vulnerability reduction terminology

probability

of exposure

risk

vulnerability

adaptation

measuresselection & design;

FRM Plan

hazard map

damage

sensitivityo

risk

map

(changes in)

driving forces

redundancy* &

adaptability**

hot spot map

protection

strategy

* tipping point analysis

** EELS analysis

o sometimes called “vulnerability”