TNC meeting, May 28-31 2013, New Orleans, Louisiana

Science & Tools: Effectiveness and Multiple Benefits of Natural Defenses/Infrastructure: How Does It Stack Up Against and Integrate

with Built Infrastructure

Dutch experiences

Jaap KwadijkDirector of Science Deltares

Flood risk in The Netherlands

20th November 2012Economically Efficient Flood Protection

Standards

2/3 flood-prone, 9 million inhabitants, 65% GNP, 1800 billion € invested value

All generations have their own flood)

1675 1682 1916 1953

4

Before 1995, Dutch reaction built infrastructure

1995, a transistion, Room for the River

?

0 0 5 15 20 25 km10100 km

zwolle

strenghtened dike

wijhe

deventer

zutphen

arnhem

westervoort

wageningenrhenen

wijk bijduurstede

leerdam geldermalsen

gorichem

zaltbommel

nijmegen

mook

boxmeer

doesburg

olst

T 1349 069en_sh

doetinchem

New standards fail proof, multifunctional Deltadikes?

New solutions to prevent floods

Building with nature, sand engine, oyster reefs (eco engineering)

Focus on ecosystem-based eco-engineering

Why should we make use of natural processes and ecosystem services in flood risk mitigation (in combination with hard engineering)?

1.Cost reduction2.Reduces risk on failure3.Adaptable

Marshland kwelders

Foto paesens-moddergat

Effective low cost low tech saltmarshproduces safety& large natural value

Dutch historical large scale land reclamation = building with nature

soft eco-engineering dike concept with reef, marsh, dune combinations

Not safe enough?

safe

Long term safety: Marshes grow with SLR

Very safereefs

Marshes/ mangroves

Sandy foreshore needs

nourishment

Wavereducing forest-dike combi ‘fort Steurgat’

Deltares/RWS concept achieves required 1/2000 safety standards and now under construction

Wave reducingwillow-tree plantationsLow cost low tech

Clay dikewill be lower than traditional design

100m wide

Vegetatie als golfremmer

Saltmarsh grows with sea level and maintains stability and safetyFlexible, low tech, low maintenance cost, longshore connectivity

Hinterland

Old dike

Muddy coastline

Wave reducing saltmarsh

Super storm stable vegetated

dune

Muddy coast Soft Safe Dike: saltmarsh/dune/dike hybridMuddy coast Soft Safe Dike: saltmarsh/dune/dike hybrid

Existing dike

500m

Artificial oyster reefs

Small scale pilot 2009

12 x 4 m

Large scale pilot 2010

Each reef: 400 m3, ± 230 tons of oyster shells

200 x 10 m

Oyster reefs as a short / midterm solution for erosion problem in the Oosterschelde

Sand Engine to cope with SLR: Experiment Observed evolution (1st year)

Measured bathymetry after 1 year

Initial

After 3 year

After 5 years

After 10 years

After 20 years

D3D Model prediction 20 years (pre-project)

Figures courtesy of Rijkswaterstaat / Shore Monitoring & Research

Measured / predicted evolution (Delft3D)

Problem: Safest delta in the world

By law (water act):

•Extremely high safety standards •Maintenance of the structures

•Detailed standards on flood prevention structures

Pro’s and con’s

• Some are extremely efficient examples (sand nourishment)

• Some are probably effective

• Potentially more adaptable

• Potentially multi purpose

• Not clear how effective the measures are

• No handbooks on design and evaluation

• Not considered as “engineering”

• Not “one size fits many”• Legal risk to implement

them