Hindcast tidal inlet of Ameland storms: January and March 2007

Abstract

During the storm season from October 2006 untill April 2007 several severe storms occurred at the North Sea. Three storm periods are selected to study the realiability of the SWAN wave model by means of a hindcast. The objective of this hindcast is to gain insight into the performance of the SWAN model, especially under storm conditions for the Hydraulic Boundary Conditions with particular emphasis upon the strengths and weaknesses of the model. The three selected stormperiods (11 and 12 January 2007, 17 and 18 January 2007 and 17 and 18 March 2007) can be described as regular western storms with wind directions varying from the southwest to the northwest and with moderate waterlevels. For these storm periods, measurements from twelve locations using the measurement network at the Tidal inlet of Ameland are used. At the start of this study, the measured wave conditions are validated agian by a consistency check. In order to prevent a selection of spurious measurements for the comparison of measured and modelled waves, all suspicious measurements are excluded from the hindcast selection. The selection of hindcasting moments is based on three different hypotheses. These hypotheses were formulated using the expected behaviour of SWAN during wind growth at shallow water, current conditions and triad interactions. In totally 31 moments are simulated (representing one third of the storms) with the current version of SWAN. The analysis of the differences between the modelled and measured wave parameters and wave spectra shows that for typical Wadden Sea conditions (wind growth over shallow water) SWAN seriously underestimates the significant wave heights. The wave period is well simulated by SWAN. The largest underestimation is observed at the buoy locations at the shallow locations. In the table below the averaged deviation (sigma factor) of SWAN in relation to the measurements is given for different areas.SB