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


\textbf{Experiment description}\newline
The field dataset collected at Egmond aan Zee in the Netherlands is used for both hydrodynamic and morphodynamic validation of the BOI-version of XBeach. Egmond aan Zee is located along the Dutch Holland coast \autoref{fig:overview_egmond}, where tides are semi-diurnal, with a neap and spring tidal range of ~1.4 and 1.8 m. Annual mean offshore wave height Hm0 = 1.3 m and wave period Tm02 = 4.5s \citep{wijnberg2002}. During northwesterly storms, significant wave heights can reach up to 7 m and storm surges can raise the water level by more than 1 m \citep{ruessink2019}. The coastal zone of the field site is characterized by 2-3 subtidal bars and an intertidal bar on a gently sloping intertidal (1:40) beach. The dune toe is located at 3 m + MSL and changes into a steep fore dune with a 1:2,5 slope. Around 14 to 17 m + MSL, the profile abruptly changes in slope and continues gently to the foredune crest at a height of 20 to 25 m+ MSL. Alongshore variability in foredune shape and height is small. During multiple years without dune erosion, embryo dunes can develop at the toe of the foredune \citep{winter2015}. The well-sorted quartz sand at the study site has a medium grain size of 250–300 µm, with a tendency to decrease in the landward direction.

A ‘quick reaction force’ was set up to collect field data directly preceding, during and following storms. The dune erosion event on 8-9 January 2019 is selected for validation. The offshore water level at the study site reached 2 m + MSL and the maximum significant wave height (Hs) was just below 5 m and maximum peak period (Tp) was 15 s. The waves arrived obliquely incident, from west-southwest during the beginning of the storm and the direction changed to the northwest for the remainder of the storm.

During the winter of 2018/2019 7 pairs of pressure sensors were deployed spaced 250 - 750 m apart, along a 1.5 – 3 km stretch of beach south of Egmond aan Zee (\autoref{fig:overview_egmond}, right panel). The pairs consist of a seaward and a landward sensor (~40m distance in cross-shore direction). The landward sensors were located above the high tide water level, each at different elevation levels (maximum 1 m difference). The surface elevations were collected at a frequency of 5 Hz and post-processed into consecutive bursts of 30 min, only the bursts in which the sensor was continuously submerged were considered, to calculate mean water levels and significant wave heights in the sea-swell (HS,SS) and infragravity (Hs,IG) frequency band. 

Full bathymetric (sonar-equipped jetski) and topographic (mobile laser scanner) surveys provided pre and post the storm observations. Bathymetric data was collected on 23 November 2018 and 22 January 2019, while topographic survey was collected directly preceding (7 January 2019) and post (10 January 2019) the storm event. The bed level measurements show that the storm did not result in large erosion volumes, but erosion of the lower dune face did occur along the entire field site. Due to the northwesterly wave incidence during the largest storms, the outer crescentic bar mostly rotated clock-wise, leading to an alternation of onshore and offshore migration alongshore. 

${tools.image(os.path.join(data_path,'Egmond'), 'overview_egmond.png', 'Location of study site (left panel). The beach poles form an alongshore reference line, with the km number referring to the distance to the zero point at the northern end of the Holland coast. The origin of the local coordinate system used (right panel) here is beach pole 41.25, with positive x and y in the seaward and southern direction, respectively. The crosses (‘x’) indicate the different pressure sensors.',label='overview_egmond',width=145)}

\textbf{Results Hydrodynamics}\newline		
The timeseries of observed and modeled water levels, high frequency and infragravity wave heights for all pressure sensors are presented in \autoref{fig:Egmond_waterlevel}, \autoref{fig:Egmond_Hm0SS} and \autoref{fig:Egmond_Hm0IG} respectively. Some of the sensors run dry during lower water elevations, especially the sensors closer to the beach (right column in the figures), explaining the gaps in the observations. The modelled surface elevations are collected at a frequency of 10 Hz and post-processed into consecutive bursts of 30 min to calculate mean water levels and significant wave heights in the sea-swell (HS,SS) and infragravity (Hs,IG) frequency band. Only the bursts for which the sensor was continuously submerged are considered.

${tools.image('Egmond/', 'XB_hydro_waterlevel.png', 'Observed water levels (black circles) against the modelled water levels (orange) for all pressure sensors. The panel in the middle shows the location of the pressure sensors, and the surrounding subpanels follow the order from North to South (top to bottom) and from sea (left) to the beach (right).',label='Egmond_waterlevel',width=165)}

${tools.image('Egmond/', 'XB_hydro_Hm0SS.png', 'Observed short-wave heights  (black circles) against the modelled short-wave heights (orange) for all pressure sensors. The panel in the middle shows the location of the pressure sensors, and the surrounding subpanels follow the order from North to South (top to bottom) and from sea (left) to the beach (right).',label='Egmond_Hm0SS',width=165)}

${tools.image('Egmond/', 'XB_hydro_Hm0IG.png', 'Observed infragravity wave heights (black circles) against the modelled infragravity wave heights (orange) for all pressure sensors. The panel in the middle shows the location of the pressure sensors, and the surrounding subpanels follow the order from North to South (top to bottom) and from sea (left) to the beach (right).',label='Egmond_Hm0IG',width=165)}

\textbf{Results Morphodynamics}\newline
The morphological model results are validated using the topography measurements of the beach and dunes, collected on January 10th. The vertical reference level of maximum dune retreat is determined at NAP + 3 m, based on the observed pre- and post-storm topography. A quantitative comparison between observed and modelled erosion volumes and dune retreat is presented in \autoref{tab:Egmond}. For transects T(y=0) and T(y=-1755), graphical comparisons are presented as well in \autoref{fig:Egmond_T_0} and \autoref{fig:Egmond_T_-1755}.

${tools.table('Egmond/', 'skill.tex', 'A quantitative comparison of modelled and observed erosion volumes [$m^3/m$] and dune retreat [m] at 3m + NAP for all 7 profiles. ', 'Egmond')} 

${tools.image('Egmond/T_0/', 'BL_BeforeAndAfterStorm_T_0.eps', 'XBeach results for cross-shore transect 0 at Egmond aan Zee. Initial bed levels are depicted by the black dotted line, observed post-storm bed levels by the black solid line and XBeach model results are presented in red. The modelled dune erosion is shown by the red shaded area.',label='Egmond_T_0',width=145)}

${tools.image('Egmond/T_-1755/', 'BL_BeforeAndAfterStorm_T_-1755.eps', 'XBeach results for cross-shore transect -1755 at Egmond aan Zee. Initial bed levels are depicted by the black dotted line, observed post-storm bed levels by the black solid line and XBeach model results are presented in red. The modelled dune erosion is shown by the red shaded area.',label='Egmond_T_-1755',width=145)}