Numerical Modelling of Aeolian Sediment Transport, Vegetation Growth and Blowout Formation in Coastal Dunes

Abstract

Coastal dunes are dominant features along much of the world’s sandy coastlines serving as the first line of protection against coastal flooding. Besides this primary purpose, the coastal dunes also provide a variety of other functions such as the supply of drinking water, nature conservation and recreational areas. With the secondary functions in mind, the Dutch coastal management strategy changed in 1990 from erosion control and stabilization of the coastline (reactive) to a policy of dynamic preservation (pro-active) with the introduction of a law called ‘’Dynamic preservation of the Dutch coast’’. This new dynamic strategy naturally induced irregularities in dunes that were completely stabilized before. One of these irregularities is the formation of a blowout. A small depression or hollow in the foredunes formed by wind erosion or wave impact may grow in time as sediment from the beach and foredunes is transported into the back dunes. In several Dutch cases such a blowout feature was artificially initiated as the exchange of sediment from the coastal system into the back dunes enhances the biodiversity significantly. Due to the high importance of the coastal dune performance as flood protection, good understanding and prediction of the (dynamic) coastal dune system is desired. Lately, general interest in this topic increased even more due to new societal challenges, such as decisions on coastal development for longer time scales, more complex management settings and sustainability. Coastal dunes and blowouts are shaped by wind induced sediment transport (aeolian sediment transport), biological - and hydrodynamic processes. To better understand and increase the predictability of dynamic systems, this study focuses on simulating the development of artificially initiated blowout features by including the combination of these relevant processes in the numerical model AeoLiS. This process-based model was originally developed to simulate aeolian sediment transport in supply-limited conditions, such as coastal areas. The study describes simulations of several academic dune formations to validate the applicability of the different (new) processes that were included in the numerical model. Finally, all processes are combined in simulations of a practical case that is used to compare numerical model results to field data on the development of multiple artificially initiated blowout features in the Dutch coast at Meijendel.