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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
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
