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Estuaries and tidal lagoons display complex morphological characteristics on both the meso- and macroscale. Single and multiple channel–shoal patterns and branching or braided patterns can be encountered on the mesoscale. On the macroscale, hypsometry of tidal basins may differ widely. Our insight in and understanding of morphodynamic processes leading to these patterns is limited. While observations and empirical relations have been established, it is only during the last two decades that macroscale models have been introduced to explain macroscale features. The emergence of mesoscale features in the long-term macroscale evolution, however, was limited to empirical and qualitative findings. Recently, mesoscale, process-based models have been introduced that show ability to reproduce mesoscale patterns in a macroscale evolution. This contribution attempts to highlight this recent capacity by bridging meso- and macroscale observations and process knowledge to increase our understanding of estuarine and tidal basin morphological evolution. It is shown that positive feedback processes leading to selforganization may be derived from first physical principles on smaller scales. In fact, this may be seen as a first successful step in the issue of aggregation of smaller estuarine process scales to larger ones.
Biogeomorphological modelling of secondary channels in the Waal river
The Waal river is a sandy, meandering part of the river Rhine, flowing through the Netherlands. To maintain safety against flooding at increased river discharges, raising the dikes is no longer opted for. Instead, measures are considered to increase the discharge capacity of the floodplains and simultaneously develop floodplain nature. One of these measures involves the reconstruction of secondary channels. The combination of increasing discharges and developing nature is conflicting. The presence of vegetation in floodplains slows down flow velocities and enhances sedimentation. Vegetation may also affect the morphological development of secondary channels. Therefore, this study investigates the natural developments of secondary channels. In particular, this study focuses on biogeomorphology - the interaction between geomorphology and biota - of three man-made secondary channels located in a floodplain of the Waal. A novel approach is that the morphodynamic development of the secondary channels, together with the vegetation succession and their interrelationships are investigated. A two-dimensional application of Delft3D is used to numerically model the hydrodynamic and morphodynamic developments of the secondary channels. A rulebased ecological model is coupled to the spatial output to predict vegetation types, succession and hydraulic roughness. The changing hydraulic roughness is fed back into the hydro- and morphodynamic modelling, to account for the changes in vegetation composition. Ultimately, the morphodynamic development of the secondary channels over a period of 30 years is simulated. This paper discusses the biogeomorphological developments in the secondary channels and presents results of the numerical modelling.
Quantifying well-being values of environmental flows for equitable decision-making : a case study of the Hamoun wetlands in Iran
A Bayesian approach to decision-making under uncertainty : an application to real-time forecasting in the River Rhine
Enhanced ablity to forecast peak discharges remains the most relevant non-structural measure for flood protection. Extended forecasting lead times are desirable as they facilitate mitigating action and response in case of extreme discharges. Forecasts remain however affected by uncertainty as an exact prognosis of water levels is inherently impossible. Here, we implement a dedicated uncertainty processer, that can be used within operational flood forecasting systems.
Spatial variability of floodplain sedimentation at the event scale in the Rhine-Meuse delta, the Netherlands
This article addresses spatial variability of comtemporary floodplain sedimentation at the event scale. Measurements of overbank deposition were carried out using sediment traps on 11 floodplain sections along the rivers Waal and Meuse in The Netherlands during the high-magnitude flood of December 1993. During the flood, sand sheets were locally deposited behind a natural levee. At distances greater than 50 to 100m from the river channel the deposits consisted mainly of silt- and clay-sized material. Observed patterns of deposition were related to floodplain topography and sediment transporting mechanisms. Though at several sites patterns were observed that suggest transport by turbulent diffusion, convection seems the dominant transporting mechanism, in particular in sections that are bordered by minor embankments. The average deposition of overbank fines ranged between 1·2 and 4·0 kg m-2 along the river Waal, and between 1·0 and 2·0 kg m-2 along the river Meuse. The estimated total accumulation of overbank fines (not including sand sheets) on the entire river Waal floodplain was 0·24 Mton, which is 19 per cent ot the total suspended sediment load transported through the river Waal during the flood.
Morphological modelling of rivers with erodible banks
A bank erosion mechanism and provisions to account for the associated planform changes and input of bank erosion products are added to a two-dimensional, depth-averaged model of river morphology. The model is applied to a reach of the meandering gravel-bed River Ohre (Eger) in the former state of Czechoslovakia. The agreement with observations is poor, but this can be ascribed to shortcomings in the flow and bed topography submodels rather than to shortcomings in the bank erosion submodel. Better results are expected when a three-dimensional flow model, equations for sediment mixtures and a bank accretion mechanism are included. This inclusion will have to be preceded by fundamental research on bank accretion mechanisms and on hiding and exposure eects in the relationship for the influence of gravity pull on sediment transport direction.
The importance of floods for bed topography and bed sediment composition : numerical modelling of Rhine bifurcation at Pannerden
Equivalent roughness of alluvial bed
Some ecological consequences of a projected deep reservoir in the Kabalebo river in Suriname
Het Waterbouwkundig Laboratorium te Delft en Onderzoek in waterbouwkundige modellen