PowerPoint-presentatie

Dune erosion during storm surges
Jaap van Thiel de Vries
19-7-2017
Picture: Beach and dunes near Westenshouwen
Delft
University of
Technology
Challenge the future
Dune erosion
Post-surge beach width
Post-surge dune
foot
Maximum storm surge level
Mean sea level
Pre-surge dune foot
Pre-surge beach width
Dune erosion
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
storm surges
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Societal importance
Hondsbosche en Pettemer sea defense
Head of Noord-Holland
Scheveningen
Head of Walcheren
Dune erosion
storm surges
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Thesis outline
Objective: Improve our physical understanding of dune
erosion in order to develop a more generic dune erosion
model.
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
Dune erosion
storm surges
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Deltaflume experiment
Dimensions: 220m x 5m x 7m
Depth scale = 6
Irregular waves; Hm0=1.5m
Dune erosion
storm surges
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Deltaflume measurements
FLUME WALL
In-situ
MOBILE FRAME
Stereo
Video
STEREO VIDEO
Dune erosion
storm surges
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Deltaflume results
Pressure sensors on flume wall:
Lange
golven
Suction tubes on shallow water frame:
Korte (wind) golven
duin
golfschot
Dune erosion
storm surges
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Deltaflume results
Dune crest
Shore line
Reflected wave
Incoming bore
Dune erosion
storm surges
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Modeling near dune hydrodynamics
The generation of long waves due to variations in the
wind generated short waves
Dune erosion
storm surges
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Modeling near dune hydrodynamics
Dune erosion
storm surges
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Modeling near dune hydrodynamics
Dune erosion
storm surges
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Near dune sediment concentrations
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.
Tbore
Dune erosion
storm surges
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Near dune sediment concentrations
Dune erosion
storm surges
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XBeach
New 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.
Dune erosion
storm surges
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LEF Restaurant en Bar
Doelenplein 2, Delft
Google maps
Dune erosion
storm surges
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