Eco-system based coastal defence: opportunities & steps to take … · 2014-12-15 ·...

Eco-system based coastal defence: opportunities & steps to take

Prof. Dr. Tom Ysebaert IMARES – Wageningen UR

Workshop “Ecological Engineering for Coastal Protection and Food Production in Bangladesh” (ECOBAS) │26 November 2014, BRAC Centre, Dhaka, Bangladesh

Introduction

Plenary by Yolanda Kakabadse (Ecuador), WWF International President

“No excuse for inaction” – She emphasized the importance of nature-based solutions in the fight against climate change. Nature-based solutions are relatively cheap to implement and maintain. “We need a different way of thinking, soft infrastructural measures, and more adaptive and flexible management.”

DELTAS IN TIMES OF CLIMATE CHANGE II

OPPORTUNITIES FOR PEOPLE, SCIENCE, CITIES AND BUSINESS

ROTTERDAM, THE NETHERLANDS, 24-26 SEPTEMBER 2014

Coastal flooding

Coastal erosion

Globally increasing need for adaptation to

coastal flood risks due to global change

(Nicholls et

al. 2007)

Especially in large cities in deltas & estuaries

in Asia, Europe, USA

(Nicholls et

al. 2007)

Conventional coastal engineering

Building dams, barriers, seawalls, embankments and revetments = widely perceived as ultimate solution to increase safety and combat flood risks in coastal areas;

However, these defences are seriously challenged and often suboptimal/negative with respect to other functions.

Furthermore, conventional engineering often exacerbates land subsidence and hinders natural accumulation of sediments.

How to adapt to increasing flood risks?

Traditional engineering

Combining with new

ecosystem-based adaptation

Emerging concept

Building with Nature

Building with Nature =

use the natural dynamics of the ecosystem to create

flexible and sustainable infrastructure while enhancing

nature values and other ecosystem services

www.ecoshape.nl

From conventional to ecosystem-based

coastal defence

(Temmerman et al. 2013 Nature)

Why use nature-based flood defence?

Why should we make use of natural processes and

natural ecosystems in flood risk mitigation (in

combination with hard engineering)?

1. Adaptable

2. Resilient, robust, sustainable

3. Cost reduction

4. Provides benefits (i.e. ecosystem services)

Traditional engineering increases flood risks in long term !

NOT SUSTAINABLE WITH GLOBAL CHANGE

(Temmerman et al. 2013 Nature)

How to adapt to increasing flood risks?

City City

Traditional engineering increases flood risks in long term !

NOT SUSTAINABLE WITH GLOBAL CHANGE

(Temmerman et al. 2013 Nature)

How to adapt to increasing flood risks?

City City

Ecosystem-based adaptation

provides LONG-TERM SUSTAINABLE flood defense

(Temmerman et al. 2013 Nature)

How to adapt to increasing flood risks?

(Temmerman et al. 2013 Nature)

Ecosystem-based adaptation

provides LONG-TERM SUSTAINABLE flood defense

How to adapt to increasing flood risks?

Ecosystem-based adaptation

often COST-EFFECTIVE

because MULTIPLE ECOSYSTEM SERVICES

(Temmerman et al. 2013 Nature)

How to adapt to increasing flood risks?

From hard barriers to soft transition zones

seawards landwards

Learn from implemented nature-based

coastal defence test cases

Test case 1 │ Sandy coasts: Sand Engine along the Dutch coast.

Test case 2 │ Estuaries, coastal bays, muddy coasts: coastal protection by ecosystem engineers: oyster reefs, mangroves.

Test case 3 │ Estuaries and deltas: Flood protection by means of management realignment and flood control areas.

Test case 4 │ Muddy coasts: Oyster Reefs for Coastal Defense and Food Production: Experience from Bangladesh (ECOBAS) (by Prof. Shahadat Hossain)

TEST CASE 1 – Sandy coasts: the sand

engine along the Dutch coast

• Netherlands: decrease of natural sediment supply owing to

● Sea level rise

● Human interventions

• Consequence: Structural erosion

• Solution: Nourishments Shoreline retreat Egmond (1679 – 1996)

Beach nourishment

• One Mega Nourishment vs long term annual nourishment

schemes

• Minimum impact on ecosystem

• Natural redistribution of sand along coastline

• Smart design to promote nature development and

recreation

• Engineers and ecologists team up

Artist impression of development – not based on science

Sand Engine Delfland: 100-150 ha, ~20 mln m3 (design)

Sand Engine Delfland: Design considerations

Construction

28 March 2011

24 May 2011

18 April 2011

11 July 2011, final layout

27 March 2013

• Much potential for Sandy Strategies worldwide

• Sand Engine concept is transferable, not SE itself

Test case 2 – Coastal protection by

ecosystem engineers

Schematic representation of how sub- and intertidal habitats are connected, and can facilitate each other directly and indirectly.

Source: Bouma et al., Coastal Engineering 2014

Ecosystem engineers:

• reduce wave energy

• trap sediment and grow with SLR

• and deliver many other ecosystem services

The role of reef structures (oysters, corals)

Construction of oyster reefs in NL

Sedimentation behind oyster reefs

Development oyster reef

Other examples – USA

Source: Cheong et al., Nature Climate Change 2013

The role of mangroves

Mangrove forests have some very important values.

● protect coastal zones against erosion and extreme weather.

● provide key nursery areas for fish and home to other animal species

● provide source of livelihood for millions of people living along tropical coastal areas.

30

Key processes of mangroves for climate

change mitigation and adaptation

Mangrove degradation and eroding

coastlines

32

• coastal squeeze • aquacultures, plantations • subsidence

Mangrove restoration to counteract coastal

erosion

massive failure of classical approach:

● small success of replanting mangroves

● counterproductive effects of hard structures

a possible way out:

● thorough system understanding: biotic and abiotic conditions

● restore mangrove habitat by restoring sediment balance

● let nature do the work: Building with Nature

Source: Han Winterwerp, Deltares

Managing mangroves for coastal defence

www.wetlands.org

TESTCASE 3 – Managed realignment

Breaching the line of defence (Breached realignment)

Lowering or removing the line of defence (Banked realignment)

Regulated tidal exchange

Managed realignment

Dike removal

New Dike

Flood control area (FCA) with controlled

reduced tide (CRT)

FCA-CRT storm flood

FCA-CRT normal tide flood

FCA-CRT normal tide ebb

Flood controlled inundation area (FCA)

Lippenbroek: 10 ha of tidal nature developping: May 2008

Flood control area (FCA) with controlled

reduced tide (CRT)

Polder management

Raise land through natural

sedimentation

Phase 1: nature

Phase 2:

aquaculture

Phase 3: farming

De Mesel et al., 2013

Testcase 4: Oyster reefs for coastal

defence and food production in Bangladesh

ECOBAS Alternative concept (BwN): using reef structures to improve coastal safety

Deliver a source of aquatic food.

Hard engineering Ecological engineering

Earthen

embankment Hard engineered

structure

KEY MESSAGE: HIGH GLOBAL POTENTIAL for

ecosystem-based adaptation to coastal flood risks

(Temmerman et al. 2013 Nature)

Steps to be taken

account quantitatively for long-term ecosystem

dynamics = essential for predictability and reliability

Source: Cheong et al., Nature Climate Change 2013

Thank you!

MORE INFORMATION:tom.ysebaert@wur.nl