LAND SUBSIDENCE, SEA LEVEL RISE

AND URBAN FLOODING COPING STRATEGIES IN COASTAL CITIES

Ger de Lange – Deltares Research Institute

Tom Bucx – Deltares Research Institute

Roelof Stuurman – Deltares Rsearch Institute

Gilles Erkens – Deltares Research Institute | Utrecht University

Land subsidence: why bother?

10 augustus 2015

Main messages:

- Land subsidence outranges climate-driven sea level rise

- Most of the problematic land subsidence is human-induced

- Solutions are available and need to be found locally

Land subsidence vs absolute sea-level rise

10 augustus 2015

Impacts of land subsidence: damage

10 augustus 2015

Differential subsidence causes:

• Damage to buildings, structures

• Infrastructure

• Sewage/gas pipes, electricity cables

(connections)

NEW ORLEANS

The DPSIR approach:

•Driving forces

•Pressures

•States

•Impacts

•Responses

Combined with the layer approach

The sinking cities assessment

10 augustus 2015

The sinking cities assessment

10 augustus 2015

1. How much subsidence is there?

2. What is causing subsidence?

A quick subsidence assessment for mega-cities:

Jakarta, Ho-Chi-Minh City, Dhaka, New Orleans, Bangkok

3. How much subsidence is predicted?

4. What impact has subsidence?

5. Who is responsible?

6. What are solutions?

The assessment aims to:

• Get insight in the

processes

• To obtain a research

agenda for this topic

• To list best practice

cases for others to

learn

NEW ORLEANS

JAKARTA

TOKYO

DHAKA

HCMC

BANGKOK

10 augustus 2015

Two strategies to deal with subsidence

• Mitigation • Works for human-induced land subsidence

• Technical: Diminish pumping, aquifer storage recovery, using lighter building materials

• Adaptation

• Works for natural and

remaining human-induced

land subsidence

• Technical: reintroducing

sediment, build higher

levees

• Non-technical: better

spatial planning,

governmental embedding

Basic requirements in any solution

10 augustus 2015

1. Better prediction • In-situ measurements • Better subsurface models and

maps • Advising on solutions: geology-

based spatial planning

2. Cost-benefit analysis

3. Choose realistic solutions

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Input View

Layers

8. Aquifer 1

7. Aquitard 1

6. Aquifer 2

5. Aquitard 2

4. Aquifer 3

3. Aquitard 3

2. Aquifer 4

1. Aquitard 4

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Level (m)

Pumping and drowning: Ho-Chi-Minh City

10 augustus 2015

Ho Long Phi, 2011

Source: Le Van Trung

presentation

10 augustus 2015

Looking for solutions in water management

An integrated approach is needed

10 augustus 2015

For a coastal city, what needs to be done:

1. Often in-situ measurements of subsidence are lacking

2. The main causes of subsidence:

a. Which part is human-induced?

b. Which part has a natural cause?

3. How much subsidence is predicted under different scenarios:

a. Socio-economic (e.g. urbanisation)

b. Climatic (sea-level rise, droughts)

4. What are the impacts on

a. Floodrisk

b. Infrastructure and construction damage

5. What parties are involved, and who is responsible?

6. What are potential solutions:

1. Technical mitigation (e.g. diminish groundwater extraction)

2. Technical adaptation (e.g. house boats)

3. Governance mitigation (e.g. getting insights in financial risks)

4. Governance adaptation (e.g. exchange of best-practises)

How to reduce (climate) vulnerability?

Tiered approach

Three steps:

1: Vulnerability scan

2: Strategy to reduce vulnerability

3: Select set of adaptation measures

Threshold

capacity

Coping

capacity

Recovery

capacity

Adaptive

capacity

time of recurrence

* 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.

Four capacities to reduce vulnerability:

Strategy to reduce flood vulnerability

Many, many options:

Lots of measures can be taken

Measures to reduce flood vulnerability

> 200 measures identified…..

Structural measures (# >100)

Collective: e.g. dikes, drainage systems

Individual: e.g. wet or dry proofing

Non-structural measures (# > 85)

Collective: e.g. FEWS, contingency plans

Individual: e.g. risk awareness, insurance

… and counting

..with our Adaptation Support Toolbox

Output: ranked list of

measures strengthened

design &

innovation

2 - 3 alternative

adaptation

packages

design ready for

decision making

ADAPTATION SUPPORT TOOLBOX

AST 3Di, HDSM,…

Dynamic Evaluation Tool

1 januari 2008

http://www.3di.nu/3di-videos/

to visualize dynamic effect of adaptation measures

10 augustus 2015

Creating resilience:

a process of dialogue, design & engineering

effects process

design

concept

model

design

effects

concept EXPERTISE

drawing calculating

dialogue

Van de Ven F.H.M., S.P. Tjallingii. P. Baan, P. van Eijk en M. Rijsberman (2005) Water in Drievoud; benaderingen voor stedelijke waterplannen

.(Triple Water; approaches for urban water management planning), Eburon, Delft, ISBN 90 5972 096

Thank you