The Netherlands is a country with a history of human activity along the coast to ensure water safety. In the 1990's a new approach to coastal management was adopted that allowed for more experimentation in the Dutch dunes. Since then a slew of different types of projects have been undertaken, one of which is the construction of foredune blowouts. Foredune blowouts are gaps or indentations in the dunes from which bare sand can erode due to the wind. The motivation for the creation of constructed foredune blowouts can range from wanting to reintroduce gradients back into the landscape to ecological restoration, or water safety.
Over the years different construction methods and designs have been created, however the evaluation of these projects has been difficult in the past due to broadly defined goals and limited monitoring data. The aim of this research is to investigate the potential of constructed foredune blowouts have in achieving water safety and preserving natural values in the Netherlands by modeling constructed foredune blowouts and evaluating the effect of various design aspects.

Insight into the effects of different designs of foredune blowouts is gained through the use of a modeling study that is set up in AeoLiS, a supply-limited aeolian sediment transport model. Different combinations of width, orientation and number of foredune blowouts are simulated in a stretched profile of a section of the Dutch Coast, leading to thirty two simulations. Additionally three alternate methods of implementing foredune blowouts as well as a scenario without a foredune blowout are simulated.

Model results show a pattern of erosion in the intertidal range and deposition along the dunefoot with limited sediment traveling from the beach through the foredune blowout. There is a clear pattern of erosion and deposition along the erosional walls of the foredune blowout and a limited development of a depositional lobe behind the blowout. Simulation of a foredune blowout induced through the removal of top soil and vegetation exhibits similarities with observations in the field.

Constructed foredune blowouts offer a method of creating areas of bare sand which can create space for ecological succession in the vicinity of the blowout. The sand that is removed may also be used to reinforce weaker areas of the dune row. They can offer a diverse looking landscape if that is desirable. However model results do not indicate that constructed foredune blowouts facilitate additional growth of the dunes. The changes in bed level in the model are primarily a redistribution of sediment already situated within the primary dune row.

Coastal aeolian sediment transport is influenced by supply-limiting factors such as sediment sorting by grain size. Sorting processes can cause a coarsening of the bed surface and influence the formation of aeolian ripples. However, it is not fully understood what influence sorting processes have on the magnitude of this transport. In this study, sorting processes of different grain sizes when interacting with wind and their influence on the magnitude of aeolian transport are investigated by performing a tracer study and developing a conceptual model. Sand grains were painted in different colors according to particle size and placed on Noordwijk beach, Netherlands. Several experiments were conducted with varying wind speeds. Surface sampling and cameras tracked the sand color movement on the bed surface, and wind speed and direction were measured. The tracer experiments show that for moderate wind conditions, ripples developed. Once the ripples have formed, the supply of finer tracer grains in downwind direction decreased over time, while the supply of coarser grains remained constant. A strong linear relationship between ripple speed and wind speed was found. For higher wind velocities, no ripples or differences in transport of grain size fractions were observed. Alternating phases of erosion and deposition of upwind sand were observed which could not be related to local variations in wind speed. Based on these results and literature, a conceptual model for an Active Bed Surface Layer (ABSL) with two regimes corresponding to moderate (I), and high (II) wind speeds was developed. The concept enables to estimate the magnitude of aeolian sediment transport as a function of wind speed, bed characteristics, and upwind sediment supply. For Regime I, a linear relationship between sediment transport and wind speed is suggested and for Regime II a third power relationship in combination with a process-based model accounting for supply limitations is suggested.