Ellis Penning, Henk Steetzel, Robbin van Santen, Jasper Fiselier,

Marieke de Lange, Vincent Vuik, Sonja Ouwerkerk, Jaap van Thiel de

Vries

NATURAL FORESHORES AS AN ALTERNATIVE

TO TRADITIONAL DIKE RE-ENFORECEMENTS:

A FIELD PILOT IN THE LARGE SHALLOW LAKE MARKERMEER,

THE NETHERLANDS

What are natural foreshores?

Long term safety:

Marshes grow

with SLR

reefs

Marshes, mangroves, reedbeds

Foreshore & beach sand nourishments

Use & produce

ecosystem services

Limited wave reduction

Enhanced wave reduction

Maximized wave reduction

What are natural foreshores?

Long term safety:

Marshes grow

with SLR

reefs

Marshes, mangroves, reedbeds

Foreshore & beach sand nourishments

Use & produce

ecosystem services

Limited wave reduction

Enhanced wave reduction

Maximized wave reduction

What are natural foreshores?

Long term safety:

Marshes grow

with SLR

reefs

Marshes, mangroves, reedbeds

Foreshore & beach sand nourishments

Use & produce

ecosystem services

Limited wave reduction

Enhanced wave reduction

Maximized wave reduction

From coastal to inland applications

Markermeer: 700 km2 Fetch: up to 40 km Avg. Depth: 2-4 meters No tides, substantial waves and water level fluctuations due to wind Managed unnatural water level: -0,4 NAP winter -0,2 NAP summer Houtridbijk splits lake Markermeer from lake IJsselmeer Houtribdijk needs maintenance (26 km)

Considerations during design phase Pilot under the National High water protection programme – innovation funds:

• Only sand nurishments applied from water - cheaper and faster

• Stable slope – steeper is cheaper

• Account for sediment consolidation of the underground

• Can vegetation aid the stability of

the construction during normal

and extreme situations

• Legal requirements

Details design

Section 1 en 4 : sand

Section 2 en 3: top layer mixed with clay

Vak 1 Vak 2 Vak 4 RestvakVak 3

zand

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zand

holoceen+zand holoceen + zand

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zand

• Each section half planted, half empty

• Willow mats with reeds (section 3 and 4)

• Exclosures to define effect of grazing

Role of vegetation

Section 1 Section 2 Section 4 Section 3

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Monitoring

4 years

• Hydrodynamics and meteorology (continuous)

wave- and flow patterns as forcing factor

• Morfodynamics (monthly)

consolidation, erosion/sedimentation due to hydrodynamics and vegetation

• Vegetation development (2x year)

safety and biodiversity

Hs = 0.9 m

Water levels under influence of wind

Morfological developments - september

Morfological developments - october

Morfological developments - november

Morfological developments - december

Morfological developments - january

Morfological developments - februari

Morfological developments - march

Morfological developments- april

Morfological developments sept-march

Wind screen

Effect interpolation

Interaction with dike

Slope development

Analyses slope development

Analyses morphological developments

First impressions

• A stable, yet dynamic foreshore

• Steep slope (1 : 10) along the waterline

• Swash-berm up to NAP+0,5 m

• Underwater plateau nearly flat at -1m NAP

• Effect of coarse sand?

Sediment grain size

Role between mean grain size and slope

Design:

D50 = 200/250 µm slope 1:30/40

Present:

D50 = 350/400 µm slope 1:10

Next steps

• Monitoring until 2018

• Use of data for improvement and validation of models

• Extrapolation to other locations

• Need for testing of extreme conditions in controlled

flume experiment