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The ebb-tidal delta of the Ameland Inlet system is of great ecological importance since it hosts a variety of benthic habitats. In a pilot project, a (mega)nourishment of 5 million cubic meters of sand was carried out on the outer ebb-tidal delta. Since the strong correlation between habitat preference and sediment characteristics on the ebb-tidal delta, it is crucial to gain insight in the mechanisms governing sediment sorting in this area. To study the initial response of grain size distribution patterns, and subsequently potential changes to benthic habitats, process-based models are useful tools. Here, we present a hydro- morphodynamic model of the Ameland Inlet which is able to simulate grain size sorting patterns. Building upon previous modelling efforts, we specifically focus on the inclusion of graded sediment transport and bed stratigraphy. The simulations, here with the nourishment excluded, reveal that the model results on grain size distribution can be related well to the forcing in combination with the local depth. Particularly, it turns out that tidal motion is responsible for the sorting pattern in the deeper parts of the ebb-tidal delta, whereas the grain size distribution in the shallower, offshore parts is particularly shaped by wind and wave processes. Model sensitivity to several numerical parameters (thickness transport layer, MORFAC) is also investigated and seems relatively small, although further investigation is needed here. A preliminary comparison reveals that the model results compare qualitatively well to field data, although the shallower offshore areas seem to be predicted too coarse in the model

Rijkswaterstaat moet een suppletiestrategie ontwikkelen en uitvoeren welke voldoet aan de veiligheidsopgave en in samenhang is met natuurbehoud en –ontwikkeling van de Nederlandse kust. Dit document beschrijft de vraagstukken voor de komende vijf jaar voor mogelijke effecten van zandsuppleties op de ecologie van de Nederlandse kust. Het doel is om te onderzoeken hoe suppletiestrategieën in de nabije toekomst kunnen bijdragen aan het kustbeheer in samenhang met het kustecosysteem. De resultaten hiervan zullen ingebed moeten worden in de suppletiepraktijk via aanpassing en/of aanvulling van de richtlijnen voor suppleren.

The relationships between water level and discharge along the river channel are vital for decision support systems in river basin management. Normally the reliability of the so-called rating curves along the river channel depends greatly on the accuracy and duration of the measured discharge and water level data. In the Elbe Decision Support System (DSS), the rating curves are combined with the HEC-6 model to investigate the effects of river engineering measures on the Elbe river system. Under such situations, the uncertainty originated from the HEC-6 model is of great importance for the reliability of the rating curves. This paper presents a two-step approach to analyze the uncertainty in the rating curves and propagate it into the vegetation model used in the Elbe DSS. The first step is to identify the uncertainty sources. An analytical method is adopted to propagate the uncertainty sources into the final rating curves. The second step is to propagate the uncertainties in the rating curves into the model outputs of the vegetation model using Monte Carlo Analysis. By this two-step uncertainty analysis approach, the uncertainty in the rating curves is successfully propagated into the vegetation model in the Elbe DSS. The final Monte Carlo Simulation results show large uncertainties in the model outputs.

Morphological modelling aims to explain and predict the changes in rivers, seas and estuaries due to these interaction. In recent history, a lot of progress has been made, especially with stability analysis approaches. However, so far only the physical interactions have been taken into account. It is known however, that biological factors are important to the dynamics of the water systems. In this paper a first step is made in the inclusion of biology into the morphodynamic models. This inclusion is based on the effect that benthic organisms have on the erodibility of the bed. This can easily be included by a change of the critical bed shear stress. These changes in the critical bed shear stress then influence the morphology. This idea has been applied to two cases. The results of the first case indicate that this approach can reproduce the influence of benthic organisms on the mud content of the bed in estuaries. The second case shows that even low numbers of organisms can influence the characteristics of large bed forms.