%%===DeltaBasin H5019.50 V4==================================================================================

In experiment V4 of the Delta Basin H5019.50 pilot experiments \cite{Boers2008} the influence of structures on erosion of dunes next to is investigated. The depth scale of the experiment is n\subscript{d} = 60, the length scale is n\subscript{l} = 120. The grain size is \SI{125}{\micro\meter}. The initial cross-shore profile is an exact 1:10 reproduction of the cross-shore profile used in the 2005/2006 Delta Flume experiments. Dikes and dune revetments consisted of a concrete layer on a fill of sand. All connections in the experiment are closed and abrupt. The water level was constant at 0.45 m above the concrete floor at the waveboard. Dunes and dikes had a crest height of 0.617 m. The dune foot revetment had a crest height of 0.50 m on top of which a 11.7 cm thick sand layer was placed. The wave conditions correspond to a Jonswap spectrum with a wave height of H\subscript{m0} = 0.15 m and peak period of T\subscript{p} = 2.07 s. 

%---RESULTS--------------------------------------------------------------------------------------------------
\autoref{fig:MR_V4CompADeltaR} presents a spatial overview of the dune crest retreat $\Delta$R\superscript{*} and the erosion volume A at t = 90 min. XBeach underestimates the erosion above the dune revetment, see dune revetment sections DR11 \& DR12 in \autoref{fig:MR_V4CompADeltaR}. To erode the dunes above the revetment waves must reach the dune front. Therefore wave runup is an important process in the development of the erosion above the revetment. Currently XBeach only simulates long wave runup. Therefore it is concluded that in agreement with the skillbed report \citep{XBTestbed2010} wave runup of short waves should also be included in the avalanching algorithm. The erosion in the revetment breach (B11) is predicted well. The predicted dune crest retreat shows a close resemblance with the measurements, see the upper panel of \autoref{fig:MR_V4CompADeltaR}. The erosion volume is slightly underestimated, see the lower panel of \autoref{fig:MR_V4CompADeltaR}.

\autoref{fig:MR_V4CompMeanDune} compares the mean dune crest retreat $\overline{$\Delta$R\subscript{*}}$, the mean erosion volume $\overline{A}$ and the mean bottom elevation $\overline{\textrm{z}\subscript{b}}$ of dune sections D1 \& D2. The predictive capabilities of XBeach in dune sections D1 \& D2 is relatively good. The predicted shape of the mean bottom elevation above SSL is similar to $\overline{\textrm{z}\subscript{b,WP}}$ derived from the profile measurements, but has an offset in seaward direction. Offshore from x = $\pm$19.5 m $\overline{\textrm{z}\subscript{b,Pred}}$ is between the minimum and maximum measured values. A bar developed seaward of x = $\pm$18.5 m which was not predicted by XBeach, see the lower panel of \autoref{fig:MR_V4CompMeanDune}. The development in time of $\overline{\Delta \textrm{R}\superscript{*}\subscript{Pred}}$ is not simulated properly by XBeach. The predicted rate of dune crest retreat decreases too rapidly in XBeach, see the upper panel of \autoref{fig:MR_V4CompMeanDune}. Despite this the predicted $\overline{\Delta \textrm{R}\superscript{*}\subscript{Pred}}$ is for roughly 66\% of the time within the standard deviation of the Argus measurements. The predicted mean erosion volume $\overline{\textrm{A}\subscript{Pred}}$ is underestimated, see the middle panel of \autoref{fig:MR_V4CompMeanDune}. This is partially explained by the fact that the foreshore in XBeach raised more than in the experiments. The development in time of $\overline{\textrm{A}\subscript{Pred}}$ is simulated well by XBeach. Generally the performance of XBeach for experiment V4 is less for experiments V1 \& V3 but is still considered relatively good.


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\begin{sidewaysfigure}[p]
	\centering\fbox{
	\psfragfig{721_Images/MR_XBeachComparison/EPS/V4/MR_CompADeltaR}}
	\caption[Spatial comparison of experiment V4 at t = 90 min]{Experiment V4: Spatial comparison at the end of the experiment at t = 90 min. Upper panel: Spatial overview of the dune crest retreat $\Delta$R\superscript{*} measured by the Argus system ({\color{blue}\rule[0.08cm]{0.4cm}{0.01cm}}), the profile measurements ({\color{black}$\bullet$}) and the XBeach prediction ({\color{red}\rule[0.08cm]{0.4cm}{0.01cm}}). Lower panel: Spatial overview of erosion volume A based on profile measurements ({\color{black}$\bullet$}) and the XBeach prediction ({\color{red}\rule[0.08cm]{0.4cm}{0.01cm}}).}
	\label{fig:MR_V4CompADeltaR}
\end{sidewaysfigure}

\begin{figure}[p]
	\centering
		\begin{tabular}{|m{13.9cm}|}
		\hline\vspace{1.75mm}
			\psfragfig{721_Images/MR_XBeachComparison/EPS/V4/Dune/MR_CompDeltaRMean}\vspace{-0.75mm}\\
			\psfragfig{721_Images/MR_XBeachComparison/EPS/V4/Dune/MR_CompAMean}\vspace{-0.75mm}\\
			\psfragfig{721_Images/MR_XBeachComparison/EPS/V4/Dune/MR_CompBottom}\vspace{3mm} \\
		\hline
	\end{tabular}
	\caption[Mean erosion parameters of D11 in Experiment V4]{Mean erosion parameters of D11 in Experiment V4. Upper panel: Mean dune crest retreat $\overline{\Delta \textrm{R}\superscript{*}}$ of 1. Argus measurements ({\color{blue}\rule[0.08cm]{0.4cm}{0.01cm}}) and its standard deviation ({\color{blue}$--$}), 2. XBeach ({\color{red}\rule[0.08cm]{0.4cm}{0.01cm}}), 3. Profile measurements ({\color{black}$\bullet$}) and its standard deviation (whiskers). Middle panel: Mean erosion volume $\overline{A}$ of 1. XBeach ({\color{red}\rule[0.08cm]{0.4cm}{0.01cm}}) and its standard deviation ({\color{red}$--$}), 2. Profile measurements ({\color{black}$\bullet$}) and its standard deviation (whiskers). Lower panel: Mean final bottom elevation $\overline{z\subscript{b}}$ of XBeach ({\color{red}\rule[0.08cm]{0.4cm}{0.01cm}}) and profile measurements ({\color{black}\rule[0.08cm]{0.4cm}{0.01cm}}), the initial bottom elevation of XBeach ({\color{red}$-\cdot-$}) and profile measurements ({\color{black}$-\cdot-$}), SSL ({\color{blue}$--$}) and minimum \& maximum measured elevation ({\color{Gray}$--$}).}
	\label{fig:MR_V4CompMeanDune}
\end{figure}