Modelling the dynamics of vegetated intertidal wetlands, such as salt marshes, comes with challenges. In these wetlands, vegetated flats are typically incised by tidal creeks. The combined effects of bottom friction and vegetation drag cause characteristic asymmetries in tidal flow patterns in these wetlands. To realistically model the hydro- and morphodynamics in such wetlands, we need high-resolution information of the bathymetry and vegetation distribution as well as appropriate boundary conditions. Specifically, for these vegetated areas the drag needs to be computed correctly. There are two sources of drag, namely bottom friction and vegetation drag. In recent years, high-resolution vegetation information and bottom friction information were used in a combined drag formulation for hydrodynamic modelling with a novel subgrid-based approach. This method improved hydrodynamic model results for vegetated intertidal wetlands (Baltus, 2022; te Booij 2024). While the model results improved, the computational grid was too coarse to adequately capture the scales of the vegetation patch distribution and accompanying tidal creeks. Insight in these detailed flow patterns is of great importance in modelling long-term development of salt marshes. To get insight in detailed flow patterns in vegetated wetland at the scale of vegetation patches, we would like te validate a recently developed subgrid-based flow velocity reconstruction for use in hydrodynamic and morphodynamic modelling of salt marshes.
You will focus on a salt marsh in the Wadden Sea around the Elbe estuary. For this area lots of hydrodynamic data is available, including the bathymetry, water levels and flow velocities. Your challenge will be to derive parameter values for the vegetation cover and to apply these in setting up a subgrid-based model. Furthermore, you will be determining the sensitivity for relation between the computational grid and subgrid scales for the flow velocity reconstruction. For this assignment, you will use the subgrid-based hydrodynamic modelling software 3Di*. The subgrid modelling approach of 3Di, enabling the numerical representation of high-resolution bed levels, has already been shown to contribute substantially to the accuracy of simulations of the characteristic tidal asymmetries in this area. Nevertheless, using high-resolution flow patterns, to enable high-resolution vegetation and morphodynamic studies, is something to be explored.
*3Di is a hydrodynamic modelling software package developed by Nelen & Schuurmans, see https://3diwatermanagement.com/
References
Baltus, O. (2022). Representing spatially variable bathymetry and vegetation in a hydrodynamic model: A subgrid-based case study in the Whitianga Estuary, New Zealand. Nelen & Schuurmans.
te Booij, B. (2024). Catching the details of mangrove dynamics: A case study in lac bay Bonaire. Nelen & Schuurmans
Other relevant information
You will be given the opportunity to analyse fieldwork data, to learn to use the hydrodynamic software package 3Di and to work with the latest extensions of this model. Through this project you will also obtain scientific and practical knowledge on field data analysis and the physics of intertidal wetlands.
Supervision
Are you interested in this assignment? Contact the Master thesis coordinator.
