|Simulating the long-term development of levee-basin topography on tidal marshes|Temmerman, S.; Govers, G.; Meire, P.; Wartel, S. (2004). Simulating the long-term development of levee-basin topography on tidal marshes. Geomorphology (Amst.) 63(1-2): 39-55. dx.doi.org/10.1016/j.geomorph.2004.03.004
In: Geomorphology. Elsevier: Amsterdam; New York; Oxford; Tokyo. ISSN 0169-555X, more
Accretion; Modelling; Numerical analysis; Salt marshes; Sediment analysis; Wetlands; ANE, Netherlands, Westerschelde [Marine Regions]; ANE, Netherlands, Westerschelde, Verdronken Land van Saeftinge [Marine Regions]; Belgium, Zeeschelde [Marine Regions]; Marine; Brackish water
Although natural levees and lower basins are typical geomorphic features along tidal marsh creeks, long-term sedimentation and elevation changes in tidal marshes were traditionally studied using 0-dimensional point models without considering spatial variations. In this study, the long-term evolution of the surface elevation of tidal marsh levees and adjacent basins was studied by applying a 0-dimensional, time-stepping model (MARSED) using spatially differentiated model parameter values for levees and basins. Firstly, the model was calibrated using field data on short-term (<1 year) spatio-temporal variations in sedimentation rates measured along four levee-basin transects within tidal marshes along the Scheldt estuary (SW Netherlands-Belgium). Secondly, the long-term (10-100 years) elevation change of the levees and basins was simulated, starting from a historically known marsh elevation. Predicted elevations were successfully validated against the present-day observed topography along each of the studied levee-basin transects. The model simulations show that the elevation difference between levees and basins tends to an equilibrium. Once levees grow 20 to 30 cm higher than the adjacent basins, the positive influence of the proximity of a tidal creek on the sedimentation rate on the levees is compensated by the negative influence on the sedimentation rate of the higher surface elevation on the levees. Once this sedimentological, geomorphic equilibrium condition is attained, both levees and basins accumulate at the same rate, which is in equilibrium with the rate of mean high water level (MHWL) rise. Finally, additional simulations show that the equilibrium elevation difference between levees and basins is mainly determined by the rate of mean sea-level rise and the incoming sediment concentration. A faster sea-level rise will result not only in a lower equilibrium elevation of the marsh surface relative to MHWL but also in a more pronounced elevation difference between levees and adjacent basins. On the other hand, higher incoming sediment concentrations will result in higher equilibrium elevations. Significantly larger elevation differences between levees and basins are only obtained for increased differences in incoming sediment concentrations between levees and basins. This study demonstrates that the long-term response of tidal marsh surfaces to different scenarios of changing sea-level and incoming sediment concentrations is not uniform in space, but that spatial variability in tidal marsh morphodynamics is important and that natural levees and inner basins will react in different ways.
- Habitat area evolution in the Western Scheldt over the last centuries, more