Aeolian Sediment Transport at the Hondsbossche Dunes

Abstract

In 2014-2015 the coastal stretch between Petten and Camperduin was strengthened by using 35 million m3 of sand. At the seaward side of the Hondbossche & Pettermer sea defence a beach and dune system was built which is called the ‘Hondsbossche Dunes’. The old sea dike has disappeared behind the new dunes and is no longer an active part of the primary flood defence system. Since 2015 the Hondbossche Dunes (HD) protect the hinterland against flooding during storm erosion events and simultaneously it creates a large opportunity for the development of new nature and recreation areas. Along the Hondsbossche Dunes five different dune profile types have been constructed to stimulate morphological dynamics of the system. The Hondsbossche Dunes have the advantage of being a dynamic system which is highly adaptive to changes in climatic forcing. This climatic forcing redistribute the marine sand from the foreshore towards the dunes. To this day, the predicted influence of aeolian sediment transport on dune development for this system is only based on previous research and expertise. For this reason, the quantification and understanding how aeolian and marine sediments are transported towards the dunes is required in order to realize an effective approach for management and maintenance of the HD system regarding to the expected sea level rise and land subsidence. The main objective of this thesis is to explore the effect of aeolian sediment transport on the morphological development of the beach and dunes at the Hondsbossche Dunes, thereby concluding on the differences in response within the five different dune profile types. A conceptual framework of the parameters that characterize the system is introduced which distinguishes three components: (1) climatic forcing, (2) sediment supply and (3) dune types. Insight into these three components is obtained by a twofold approach: a data-analysis at the JARKUS transects for the first 19 months after construction and the application of the wind sediment transport model AeoLiS at a two-dimensional scale. The results obtained from the data-analysis show that an alongshore variations in beach and dune development is strongly present, for which the morphological changes were most pronounced in the seven months after construction. High beach volume losses were observed along the Hondsbossche Dunes. The volumetric losses were transported in alongshore direction leading to accretion of the beaches. Besides, volumetric losses were transported in cross-shore direction resulting in an average dune growth of 28 m3/m/y. The supply-limited model overestimates the measurements with a factor varying from 1.2 to 3. The model shows to predict alongshore variations in dune growth as a result of spatial variations in sediment availability regarding to topography and grain size characteristics. It is seen that the five man-made profile types show an appreciable different response to the aeolian sediment transport towards the dunes. Dune growth of a profile type is likely to be determined by: (1) a temporal variability in local processes that determines the aeolian sediment supply towards the dunes and (2) the dune geometry that determines the capacity of the profile type to capture the sediments.