The impact of gustiness on sea surface height in storm surge situations

In this study the influence of wind gusts on sea surface height in storm surge situations is investigated. The storm surge model WAQUA/DCSM is used for this purpose. Gustiness was modelled in Monte Carlo experiments of idealised uniform wind fields. It is concluded that high gustiness amplifies a storm surge. This is due to the non-linear behaviour of the drag relation that defines the amount of surface stress on the water.

A parameterisation for the effect that is found in the Monte Carlo experiments is presented and verified with a non-uniform wind field. The parameterisation was used in the model (called new model). In this way a model with implicit gustiness (traditional model) and explicit addition of gustiness (new model) could be compared.

With ECMWF fields of wind, pressure and wind gust (only for in the new model) sea surface heights were simulated for the storm surge season 2007 - 2008. The results of the simulations of the new model were compared with those of the traditional model and observations of gauges along the Dutch coast. The new model deviates from the traditional model in high storm surge cases.

In a statistical analysis of the two models and the observations, we found that there is no clear correlation between the error of WAQUA/DCSM and the addition in surge due to gustiness. Furthermore, the range of the error of WAQUA/DCSM is far larger than the addition due to gustiness. It is thus concluded that for the moment it is not important to include explicit gustiness in the WAQUA/DCSM model. When large errors in WAQUA/DCSM are diminished, it can become more necessary.