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During test T01, T02 and T03 of the 2006 Deltaflume experiment \citep{VanGent2008} the effect of the wave period on dune erosion was examined. It was found that the dune erosion volume increases for a larger wave period, which is caused by a larger flow related sediment transport. In addition, the increase in flow related sediment transport is mainly a result of a higher mean sediment concentration whereas the time and depth averaged flow velocity has the same order of magnitude within the range of wave periods examined.  
The aim of this subsection is to examine the processes, which cause the wave period effect in the model and to what extent these processes are in line with the mechanisms observed in the measurements. To this end test T01, T02 and T03 of the Delta-flume experiment are simulated. The simulations are 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 Tm-1,0 wave period. Settings for the wave energy dissipation model are found in Table 1 and other setting are defaults as listed in in Appendix X. 
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In Figure 1 simulated profile evolution during the tests compares well with the measured profile evolution. However, the bar type feature at the offshore edge of the developing foreshore is not reproduced in the simulations. Comparing measured and simulated dune erosion volumes in Figure 2 it is seen that for test T03 the erosion volume after 1 hour and 2.04 hours of waves is underestimated whereas for test T01 and T02 simulated erosion volumes are reasonably well predicted over all test inter-vals.
Figure 1 Simulated profile evolution (dashed lines) for test T01 (upper panel), test T02 (middle panel) and test T03 (lower panel) compared with measured profile evolution (solid lines) after t = 0.0, 0.1, 0.3, 1.0, 2.04 and 6.0 hours.
Figure 2 Simulated dune erosion volume above still water level (dashed lines) for test T01 (open squares), T02 (open triangles) and T03 (open circles) compared with measured dune erosion volume (solid lines) for test T01 (closed squares), T02 (closed triangles) and T03 (closed circles) as function of time.
Simulated time and depth averaged flows are compared in Figure 3, which shows that the mean flow slightly increases with a larger wave period (6\% between x = 170 m and x = 205 m). This tends to be a slightly different trend than observed in the measurements that show a 3\% increase in the same cross-shore area. It is remarked though that any firm conclusions cannot be made since the measured time and depth averaged flow velocities are based on limited sensors over depth (and for that reason it was concluded that the mean flows for test T01 and T03 are compa-rable). 
The increase in the simulated offshore directed mean flow is caused by an increase of the short wave related mass flux whereas the roller related mass flux is only slightly different. The maximum long wave related mean flow is larger during test T01 than during test T03.
Figure 3 Simulated test and depth averaged flow associated with short waves (dashed-dotted line), rollers (dotted line) and long waves (dashed line) for test T01 (left panel) and test T03 (right panel). The simulated total test and depth averaged flow (solid line) is com-pared with measurements (squares).
Simulated sediment concentrations are compared with measurements in Figure 4 and show an O(60\%) increase in the mean sediment concentration for a larger wave period between x = 170 m and x = 205 m. This increase is comparable as observed in the measurements (O(60\%) for the test and depth averaged sediment concentration). The simulated mean sediment concentration is underestimated with O(40\%) com-pared to the measurements between x = 170 m and x = 205 m for both model simulations.
Figure 4 Simulated mean sediment concentration (solid line) compared with test and depth averaged sediment concentrations obtained from the suction tubes (squares) for test T01 (left panel) and test T03 (right panel).
It is concluded that the effect of the wave period on dune erosion and dune face retreat is favourably predicted with the XBeach model. The simulated increase in dune erosion with a larger wave period is mainly caused by an increase of the mean sediment concentration of O(60\%), which is comparable to the measurements. The near dune return flow slightly increases with approximately 6\% for a larger wave period. However, the accuracy of measured time and depth averaged flows is insufficient to verify this increase.

The following results are obtained during the last test run:

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${tools.image('Deltaflume2006/T02/', 'hydro.png')}
${tools.image('Deltaflume2006/T02/', 'morpho.png')}
