Abstract
This PhD-thesis investigated the effect of future climate change on dune erosion in the Netherlands. At present, dune erosion occurs under a combination of large storm surge and high waves, which are both generated by a storm event. Therefore to investigate the affect of future climate change on dune erosion
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requires an analysis of various aspects of the offshore hydrodynamical condition, specially on the affect of future projected changes in wave, wind and sea level rise After the 1953 storm surge disaster, which resulted in widespread flooding in the Netherlands, Belgium and the United Kingdom, regulations were adopted that implied that dunes should be able to withstand offshore storm events with a return frequency of 1:10,000 year. Previously the effect of climate change on 1:10,000 year storm surge levels was investigated. However the effect on 1:10,000 year wave conditions was not considered. To investigate this, wind and sea level pressure data from the 17-member ESSENCE-ensemble and the moderate A1b-emission scenario were adopted as a forcing for the NEDWAM wave model. It was concluded that the 1:10,000 year wave condition is not expected to change under future projected forcing. Second, future extreme wind conditions were analysed. To address this, extreme wind conditions from 12 climate models (GCMs) under the moderate rcp4.5 and the extreme rcp8.5 scenario were analysed. All models project large interannual variability, however there is no change in annual maximum wind speed or wind speed with return periods up to 1:500 year compared to present day. Additionally, there is no increase in annual maximum wind coming from north-west, the dominant wind direction to generate large storm surge and waves and hence severe dune erosion. It is noted however that there is considerable model variability. From these analyses it is not expected under future A1b, rcp4.5 and rcp8.5 conditions that storm surge levels and extreme wave characteristics will change. To analyse the effect of sea level rise on dune erosion, the dune erosion model XBeach was calibrated and validated, using wave observations and pre- and post-storm dune surveys south of Egmond aan Zee, the Netherlands. The calibrated XBeach predicted the overall magnitude and the alongshore variations of the observations reasonably well. This calibrated model was used to analyse the effect of different future sea level rise scenarios and of different wave angles for Egmond and Noordwijk aan Zee. For both sites, XBeach predicted a linear dependence of the erosion volume on sea level rise. In all simulations the erosion dominating infragravity waves remain the same compared to present day. The cause of the increase in erosion is the higher level of attack on the dune face due to higher sea surface height. Under future projections of climate change, the predominant mechanism driving changes in dune erosion is the rise in sea level and to a lesser extent changes in wind, wave and storm surges.
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