Modelling shoreface profile evolution

Current knowledge of hydro-, sediment and morpho-dynamics in the shoreface environment is insufficient to undertake shoreface-profile evolution modelling on the basis of first physical principles. We propose a simple, panel-type model to map observed behaviour. The internal dynamics are determined by slope-dependent, wave-induced cross-shoreface transports, while the external driving factors are lateral sediment supply and sea-level rise. This model concept is tested with reasonable success against the observed behaviour of the Central Holland Coast, considering two hindcast periods, one covering the evolution over the last century, the other the Subboreal/Subatlantic evolution.\ud \ud A limitation of this model is that the cross-shoreface dynamics are solely steered by the variations of shoaling, short waves. Since a variety of other wave and current dynamics may be expected to be present in the coastal boundary layer, it may well be that the effects of the mechanisms and conditions which are not represented are hidden in the coefficients of the sediment-transport formula. This limits the accuracy of the coefficients as used, and our findings should be considered as an-order-of-magnitude estimate only. Indeed, behaviour-oriented modelling implies that generalization of results to arbitrary situations and conditions is not straightforward. Yet, we expect that some of the conclusions are more generally applicable.\ud \ud This concerns the substantiation of the assumption that the upper shoreface responds on a much smaller time scale than the lower shoreface, and the idea that the shoreface profile is not always and everywhere in equilibrium with its forcing. A worthwhile observation from the Holland Coast application is, that the bottom slope effect on the transport is only important at geological time scales. The profile evolution at the engineering time scales (say 10 to 100 years) is effectively quasi-static, in that there is no feedback between the long-term averaged transport and the state of the profile. This implies that at these smaller scales the profile changes can be predicted on the basis of a static sediment balance. This does not mean that the gravitational downslope transport is unimportant as a physical phenomenon in coastal profile evolution: It is only unimportant if a highly aggregated model like this is applied at relatively short time scales

Cross-shore stratified tidal flow seaward of a mega-nourishment

The Sand Engine is a 21.5 million m3 experimental mega-nourishment project that was built in 2011 along the Dutch coast. This intervention created a discontinuity in the previous straight sandy coastline, altering the local hydrodynamics in a region that is in influenced by the buoyant plume generated by the Rhine River. This work investigates the response of the cross-shore stratified tidal flow to the coastal protrusion created by the Sand Engine emplacement by using a 13 hour velocity and density survey. Observations document the development of strong baroclinic-induced cross-shore exchange currents dictated by the intrusion of the river plume fronts as well as the classic tidal straining which are found to extend further into the nearshore (from 12 to 6m depth), otherwise believed to be a mixed zone

Vers un nouveau plan delta pour garder les Pays-Bas à l’abri des inondations au cours du 21

Le Gouvernement néerlandais a récemment présenté des recommandations d’une portée considérable sur la manière de garder le pays à l’abri des inondations au cours du siècle à venir, étant donné la probabilité d’élévation du niveau de la mer et d’augmentation du débit des fleuves. Cet article explique quelles sont ces recommandations, qui reposent sur une réévaluation progressive des normes de sécurité, à la lumière de la croissance économique et du risque de victimes multiples, ainsi que les signaux fournis par les débats et les connaissances sur le changement climatique. Il conclut que la protection est réalisable à la fois d’un point de vue technique et d’un point de vue économique, pour un coût pouvant aller jusqu’à 3 milliards € par an, et que l’approche pourrait être utile à d’autres régions basses côtières situées au-dessous du niveau de la mer

Coping with Coastal Change

This chapter focuses on how to cope with coastal change and its implications. There are two major types of response: mitigation representing source control of drivers, such as greenhouse gas emissions and groundwater withdrawal, and adaptation referring to behavioral changes that range from individual actions to collective coastal management policy, such as upgraded defence systems, warning systems and land management approaches. Coping with coastal change involves analysis of all the drivers of change. All coping responses need to be consistent with wider societal and development objectives, and hence require implementation within an integrated coastal management philosophy. Proactive adaptation plans are already being formulated for urban areas such as London, the Netherlands and Ho Chi Min City. Some of the major adaptation challenges are in many developing countries, reflecting a large adaptation deficit; deltaic areas and small islands are the most vulnerable settings