11-04-23

Challenge the future

DelftUniversity ofTechnology

Dune erosion during storm surgesJaap van Thiel de Vries

Picture: Beach and dunes near Westenshouwen

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Dune erosion

Maximum storm surge level

Pre-surge dune foot

Post-surge dune foot

Pre-surge beach width

Post-surge beach width

Mean sea level

Dune erosion during storm surges

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Societal importance

Dutch safety policy against flooding:

•“Dijkringen”

•Weakest link in a “dijkring” determines safety against flooding

•Strength primary water defenses against normative conditions is assessed every five years.

•Strength dunes is assessed with empirical guideline elaborated from large scale dune erosion experiments

Dune erosion during storm surges

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Societal importanceHondsbosche en Pettemer sea defense Scheveningen

Head of Noord-Holland Head of Walcheren

Dune erosion during storm surges

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Thesis outline

Thesis outline:• Large scale dune erosion tests in the Deltaflume• Interaction of dune and swash• New approach in modeling near dune hydrodynamics• New approach in modeling near dune sediment

concentrations• Coupling of new physical insights in a 2DH

morphodynamic model

Objective: Improve our physical understanding of dune erosion in order to develop a more generic dune erosion model.

Dune erosion during storm surges

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Deltaflume experimentDimensions: 220m x 5m x 7m

Depth scale = 6

Irregular waves; Hm0=1.5m

Dune erosion during storm surges

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Deltaflume measurements

In-situ

Stereo Video

Dune erosion during storm surges

MOBILE FRAME

STEREO VIDEO

FLUME WALL

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Deltaflume results

Pressure sensors on flume wall: Suction tubes on shallow water frame:

Dune erosion during storm surges

duingolfschot

Korte (wind) golvenLange golven

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Deltaflume results

Incoming bore

Shore line

Reflected wave

Dune crest

Dune erosion during storm surges

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Modeling near dune hydrodynamics

The generation of long waves due to variations in the wind generated short waves

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Modeling near dune hydrodynamics

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Modeling near dune hydrodynamics

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Near dune sediment concentrations

Tbore

Hypthesis: High near dune sediment concentrations are caused by wave breaking induced turbulence that is injected in the water column over a short time interval and reaches the bed as a pulse.

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Near dune sediment concentrations

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XBeachNew physical insights are coupled in the morphodynamic model XBeach that:

• Solves both short waves (energy balance) and long waves (Nonlinear Shallow Water Equations);

• Includes a formulation that also relates the sediment concentration to the wave breaking induced turbulence pulses that potentially reach the bed;

• Includes the longshore direction.

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