Efficient modelling of ecomorphodynamics in estuaries to evaluate salt-intrusion solutions

Type
PhD research

Duration
March 2020 till March 2024

Persons involved:
Ir. Rutger W.A. Siemes (PhD-student)
Dr. Ir. T.M. Duong (daily supervisor, co-promotor)
Dr. Ir. B.W. Borsje (co-promotor)
Prof. dr. S.J.M.H. Hulscher (promotor) 

Funding
NWO Perspectief-programma: SALTISolutions, NWO Simon Stevin Meester Grant,
TGS-bridging grant

Summary of the research
Salt-intrusion is a significant problem in estuarine regions worldwide. Measures for mitigating salt-intrusion can be categorized as traditional ‘grey’ engineering or ‘green’ nature-based engineering. Traditional measures (e.g. dams) are robust but not resilient in the face of climate change. Nature-based measures (e.g. oyster beds, sand waves) have dynamics on their own as they might be able to adapt to long-term changes. This also means that interplay between physical processes (water movement, sediment transport, bed level changes) and ecological processes (oyster bed dynamics) on salt dynamics on the estuarine scale has to be assessed (i.e. the ecomorphodynamics). However, an ecomorphodynamic model that is able to evaluate nature-based solutions to counteract salt-intrusion on the estuarine spatial scale for time scales of up to 100 years (i.e. including climate change) is missing.

A high-fidelity model will be constructed of the Rhine-Meuse delta. This high-fidelity will be in 3D and includes tides and wind waves (sea-side) and discharge waves (river-side) and surface forcing as well as sediment transport and bed evolution. Such a high-fidelity model requires substantial computational efforts, especially for long-term modelling. To make the study of estuarine processes and long-term modelling feasible, a surrogate model will be constructed as well. Surrogates can be either a lower-fidelity model where the initial model is simplified or response surface surrogates which use statistical or empirical data-driven models to emulate the original systems, e.g. artificial neural networks. Such models can approximate the response pattern of a high-fidelity model and thus reduce computational efforts.

With the surrogate model, we will investigate how ecomorphodynamic processes at the estuarine bed affect development of the estuary sides (wetlands). In addition, the influence of ecomorphological development at the estuarine bed and estuarine sides on salt dynamics will be researched. Furthermore, we will apply climate change scenario’s to assess their impact within the estuary on salt intrusion problems. Finally, nature-based solutions (i.e. artificial sand waves, wetlands or oyster beds) will be implemented to assess their influence on salt dynamics for present and future, incorporating the created CC scenario’s.

Keywords
salt intrusion; nature-based solutions; estuarie scale; Rhine-Meuse Delta; estuarine bed; wetlands; ecomorphodynamics; process-based model; surrogate model; bed forms; climate change