B. van Westen1, S. de Vries2, A.J.H.M Reniers2, J.P. den Bieman1, B.M. Hoonhout3
Coastal dunes serve as a first line of protection against flooding by the sea. In the recent past, the interest in secondary services provided by coastal dunes, such as ecological values and recreation, has increased. To manage and maintain the coastal as an attractive area that combines these services, the natural dynamics must be understood. In view of this, numerical models with quantitative predictive capabilities on the development of coastal dunes provide a useful tool for coastal zone managers. Several models related to aeolian sediment transport and dune development are currently available, but none of these individual models is currently used for engineering purposes. The aim is to improve the current aeolian modelling state of the art by coupling capabilities from different existing models, developing a modular aeolian transport model with quantitative predictive capabilities for dune development.
We have combined model formulations of three aeolian transport and dune models. The AeoLiS model (Hoonhout and de Vries, 2016) is a process-based aeolian sediment transport model with spatiotemporal varying sediment availability, capable of simulating both supply- and transport-limited situations. Coastal Dune Model (CDM) (Durán and Moore, 2013) does contain dune building processes including a quantitative description of turbulent flow fields over smooth hills, a continuum saltation model and avalanching. In cases where beach dune vegetation dynamics are significant, Dune-Beach-Vegetation (DUBEVEG) (De Groot, 2012) provides a practical implementation of vegetation dynamics. The supply-limited approach from AeoLiS is combined with the dune development processes and general formulas for vegetation growth and their influence on the shear stresses from CDM. Vegetation parameters as vertical growth, sediment burial tolerance, germination and lateral expansion are adapted from DUBEVEG. To reproduce the influence of the sea, marine sediment supply in the intertidal zone and the mechanical erosion of sediment and vegetation during extreme events are implemented as well.
The combined model is now capable of simulating barchan dunes (Figure 1a) and parabolic dunes (partly). The inclusion of seed germination and lateral vegetation expansion causes the growth of randomly located hummocks, creating embryonal dune fields (Figure 1b). The modular structure of the model makes it possible to couple it to hydrodynamic-, groundwater- or vegetation-models, with the eventual possibility to simulate complete coastal areas. The model can potentially be used to determine the influence of tidal ranges, storm frequencies, armoring, salinity and precipitation on dune building processes. This will result in a greater insight in the general behavior of coastal systems, including the evolution of embryonal dune fields as well as foredune characteristics like maximum height and auto cyclic formation of transversal dunes. On the other hand, the model can also be used during more practical situations such as computing recovery times of coastal dunes after extreme events or for the creation of artificial blowouts.
Figure 1 Simulation results of the coupled approach of (a) barchan dunes and (b) embryonal dune field.