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\textbf{Experiment description}\newline
One of the most memorable storm surges in recent history, is the storm surge in early February of 1953, leading up to the flooding of large areas in the southwest of the Netherlands and resulting in hundreds of casualties. The storm surge was especially disastrous because of the occurrence of the worst case scenario where a storm surge coincides with spring tide. A very strong northwesterly storm and spring tide led to one of the largest natural disasters (called the ‘Watersnoodramp’). It was one of the main causes for the initiation of the Dutch Delta plan, with the primary goal to increase and regulate the water security of the Dutch coast.

Because the event occurred in 1953, the amount of available data is limited. As such, a coastal profile representative for the Dutch coast is applied as pre-storm profile. For the hydrodynamic conditions, a combination of satellite derived reanalysis data, ERA5 \citep{bell2020} and literature \citep{gerritsen2005happened} is used. Finally, the properties of the simulated post-storm profile will be compared to reported dune erosion \citep{VanThielDeVries2009}, reported at around 90 m3/m and changes in dune foot location that are available from \citet{ruessink2002dunefoot}, ranging from 8 to 16 meters along the Dutch coast. Because of this, the main focus of this validation case will be the morphological in nature.

Using the available data, as explained in more detail in the following sections, boundary conditions are reconstructed, representative for the coastal section between Hoek van Holland – Scheveningen (\autoref{fig:overview_holland1953}).

The resulting hydraulic boundary conditions, explained in more detail below, are as follows:
\begin{itemize}
	\item The peak surge level consisting of high (spring) tide and storm surge is 4.0 m +NAP.
	\item The peak significant wave height Hs during the storm is 7.3 meters.
	\item The maximum wave peak period Tp is 14.1 seconds.
\end{itemize}

${tools.image(os.path.join(data_path,'Holland1953'), 'overview_holland1953.png', 'Overview of the extent of the southern part of the Dutch coast (Hoek van Holland to IJmuiden) and the location of the ERA5 data.' ,label='overview_holland1953', width=145)}

\textbf{Results}\newline		
Just like the pre-storm profile data, the post-storm data for the 1953 storm event is fairly limited. From \citet{VanThielDeVries2009}, a representative range for the dune erosion above storm surge level along the Dutch coast is available: 90 ± 26 m\textsuperscript{3}/m (with 90 m\textsuperscript{3}/m being the mean of all observations and 26 m\textsuperscript{3}/m being equal to 1 standard deviation). From \citet{ruessink2002dunefoot}, the cross-shore displacement of the dunefoot along the Dutch coast through the years is available. Looking at the 1953 timeframe specifically, a noticeable negative displacement (i.e. erosion) can be observed for all locations along the Delta coast (Walcheren and Schouwen) and the Dutch coast (Hoek van Holland to Den Helder). The displacement at Vlieland and Terschelling is less pronounced. Assuming that the entire displacement within this specific measurement interval is the result of the 1953 storm surge, the resulting dunefoot erosion can be deduced. An uncertainty range of ± 1.5 m is added due to the visual deduction method. The southern-most coastal sections show the largest dune foot erosion of up to 16.5 ± 1.5 m. Towards the north, the dunefoot erosion gradually reduces, down to 8.5 ± 1.5 m at Den Helder, possibly due to the increasing time difference between the peak waves and the peak water level, as was previously discussed. The source does not specifically mention the height at which the retreat is measured, a height of 1 meter above maximum storm surge level (i.e. 5 m +NAP) is assumed.

In \autoref{fig:Holland1953}, the predicted dune erosion due to the 1953-storm is presented and compared to the ranges of observed dune erosion and retreat.

${tools.image('Holland1953/', 'BL_BeforeAndAfterStorm_BOI.eps', 'Pre and post storm surge profile as computed by XBeach. Upper frame shows the dune erosion section, the lower frame shows the entire XBeach profile.',label='Holland1953', width=145)}

