<%namespace name="tools" file="tools.tex"/>

Test T04 of the Deltaflume experiment 2006 \citep{VanGent2008} is carried out with an initial profile that contains a small dune in front of a larger volume dune that collapses after approximately one hour of waves (interval C and D). After breaching of the small dune, the foreshore is already very efficient in reducing wave impacts on the dune face resulting in small erosion rates over the remaining test intervals. In this test it is examined to what extent the dune breach can be reproduced with the XBeach model and whether the (substantially smaller) erosion rate at the end of a storm is correctly predicted. The simulations is performed on a regular grid with dx = 1 m and input to the model are time series of short wave varying energy (low pass filtered on the wave group time scale) and incoming (bound) long waves. The time series are constructed from pressure and flow measurements at x = 41 m from the wave board. The short wave group velocity (associated with advection of wave action) is based on the $T_{m-1,0}$ wave period. Settings for the wave energy dissipation model are equal to the settings for the T03 test.

Simulated profile evolution and dune erosion volumes are shown in \autoref{fig:deltaflume2006_t04_profile} and \autoref{fig:deltaflume2006_t04_morpho} respectively. The simulated hydrodynamics are presented in \autoref{fig:deltaflume2006_t04_hydro}. For the first three intervals (the small dune breaches in interval 3) the dune erosion rate is slightly overestimated but the profile evolution compares favourably with the measured profiles. Considering the last two intervals, erosion rates and dune face retreat are too large. 

Breaching of a small dune in front of a larger volume dune causes that suddenly the foreshore is significantly closer to equilibrium with the storm surge conditions. As a result near shore hydrodynamics, near shore sediment transports and wave impacts on the dune face are less severe. It is concluded that the feedback between profile evolution and near dune processes is not sufficiently well included in the model at the end of test T04, which is representative for conditions at the end of a storm. More insight in the model performance at the end of a storm could possibly be obtained by comparing the evolution of simulated driving processes (undertow, sediment concentrations and avalanching) with measurements. 

${tools.image('Deltaflume2006/T04/', 'T04_profiles.eps', 'Profile development during test T04', 'deltaflume2006_t04_profile')}
${tools.image('Deltaflume2006/T04/', 'T04_morpho.eps', 'Erosion pattern and volumes and retreat distance during test T04', 'deltaflume2006_t04_morpho')}
${tools.image('Deltaflume2006/T04/', 'T04_hydro.eps', 'Hydrodynamics during test T04', 'deltaflume2006_t04_hydro')}
