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Morphological development after the July 2014 flow slide on the tidal flat of Walsoorden in the Western Scheldt
A large flow slide occurred at the tidal flat of Walsoorden in July 2014. A flow slide occurs when the slope is sufficient steep and a trigger starts the process of liquefaction or breaching. A measurement campaign was initiated to measure the bathymetry around the tidal flat, starting a few months before the flow slide. After the event monthly measurements were taken to monitor the development of the area. Based on the bathymetry measurements, the volume changes in the channel and in the gap were determined. An existing Delft3D model schematisation of the Western Scheldt was used to calculate the morphological development. The model was setup around the tidal flat of Walsoorden. The morphological changes determined by the model are different from the bathymetric changes found in the measurements. In the model the sediment accretion smoothens out; the sediment is deposited on the sides of the accumulation. Most of the sediment from the channel is transported in ebb direction. The model shows almost no sedimentation in the gap, which is contradictive with the measurements. The sensitivity of the model was tested to investigate the differences between the observations and the model.
Operationalizing socio-economic and climate tipping points
The objective of this deliverable is to operationalize the concept of tipping points within COACCH. Tipping points are an important notion in climate change research and communication. Tipping of large elements of the climate system may cause rapid change in the biophysical system (e.g. accelerated sea level rise) which has profound consequences for the socio-economic structure of Europe. However, also gradual changes in climatic conditions may significantly and abruptly alter socio-economic structures in Europe. COACCH therefore set out to significantly advance the knowledge on climate tipping elements and socio-economic tipping points induced by climate change.
Climate change induced salinization of drinking water inlets along a tidal branch of the Rhine River : impact assessment and an adaptive strategy for water resources management
This study presents the results of an impact analysis of climate change on salinization and the long-term availability of drinking water resources along the river Lek, a tidal branch of the Rhine delta, and a potential mitigation measure. To this end, a one-dimensional modelling approach was used that enabled studying 50 years of variation in discharge and tide in current and future climate. It was found that all locations are increasingly vulnerable to salt intrusion caused by the combination of sea level rise and decreasing river discharges. This affects both the yearly average chloride concentration and long duration exceedances of the threshold value of 150 mg/L. It was also found that diverting a higher fresh water discharge to the Lek of several tens of cubic meters per second reduces the risk of salinization at the upstream inlet locations. However, the increased influence of seawater intrusion on the drinking water inlets cannot be fully compensated for by this measure. The potential gain of the extra water for the drinking water inlets along the Lek has to be balanced against the impact of this measure on water levels and stream flows in other parts of the river system.
Morfologisch advies broedeilanden : veiligstellen De Bol
Dit rapport beschrijft een verkennende morfologische studie naar de aanleg van een zandsuppletie ter bescherming (versterking) van het bestaande broedeiland De Bol op het plaatcomplex Hooge Platen (Westerschelde). De doelstelling van de suppletie is het broedareaal op De Bol veiligstellen.
Morfologisch advies broedeilanden : broedeiland Plaat van Walsoorden
Dit rapport beschrijft de morfologische haalbaarheidsstudie naar een broedeiland op de locatie Plaat van Walsoorden.
Government facilitation of external initiatives : how Dutch water authorities cope with value dilemmas
Water authorities search for new collaborations with non-governmental actors, with the aim of facilitating societal initiatives. A comparative case study was conducted to analyze the value dilemmas faced by water authorities when they choose to facilitate and how they cope with these dilemmas. The study found that the most prevalent dilemma is between traditional democratic values and efficiency-related values. In the chosen solutions, the latter seem to prevail over the former. Casuistry, cycling and hybridization are common coping mechanisms. The study shows the potential of non-governmental initiatives in the water sector while also reflecting critically on dominant administrative values.
Modeling the morphodynamics of the mouth of the Scheldt estuary
Recent research on the Scheldt estuary mainly focused on the Western Scheldt. There is now a renewed interest in the mouth of the estuary as the Flemish government explores the feasibility of large-scale morphological interventions in that area. This paper describes the ongoing development of a process-based numerical model (Delft3D) of the Scheldt estuary. The so-called Delft3D-NeVla model computes morphodynamics forced by waves, tide, wind and river discharge, and affected by sediment dredging and dumping to maintain navigation channels at the desired depth. After further calibration and validation, the Delft3D-NeVla model will become an important tool to understand and predict the morphodynamics of the mouth of the estuary due to natural processes and large-scale morphological interventions such as relocation of navigation channels.
Simulation of long-term morphodynamics of the Western Scheldt
In this paper we use a 2D process-based model to hindcast morphodynamic behavior of the Western Scheldt estuary. The periods of 1860-1970 (110 years) and 1905-1970 (65 years) are simulated. We compare the results to a historically unique dataset of bathymetric maps. The results show that the model results get better over time. The results show that the model is capable of simulating the large scale erosion and sedimentation that has occurred in the considered period. We attribute this to the self-organization of both the model and reality. The interaction between the major tidal forcing and the estuaries' fixed outline overrules other uncertainties over long time scales. Our research shows that process-based models applied in confined environments and under constant forcing conditions may perform well especially on long time scales. This makes them potentially suitable for centennial time scale forecasts related to, for example, climate change.
Sustainability of the multi-channel system in the Westerschelde under influence of dredging and disposal
This paper presents an on-going study meant to improve our knowledge on the morphological development of estuaries for supporting estuarine management considering accessibility for navigation and the ecological value. We focus on the question whether a multi-channel system in the Westerschelde can be sustained under pressure of future deepening and maintenance. After reviewing the previous work on this subject the remaining questions are inventoried and further research for answering each question is proposed. The results of the proposed study will directly be applicable for developing better strategies for disposal dredged sediments, supporting decision making concerning sand mining and further deepening of navigation channels, and for monitoring the effects of human activities on the morphological development in the estuary.
Transport of fine sediments in a narrow converging estuary : the Sea Scheldt
In this paper we study the transport of fine sediments by river-induced flushing, estuarine circulation and tidal asymmetry in the Sea Scheldt, Belgium. This study is carried out with an idealized schematization of the river, modeled as an exponentially converging river with constant depth and rectangular cross section, using Delft3D. Sediment is only imported from the lower sea boundary. Values for tidal amplitude and river flow, prescribed at the models’ open boundaries are comparable to those in the Scheldt. We show that a turbidity maximum is formed at the head of the salinity intrusion, driven by estuarine circulation, and in balance with river-induced flushing. For the given conditions, the model does not predict any fine sediment transport beyond that turbidity maximum.