Constructing notches in foredunes: Effect on sediment dynamics in the dune hinterland

Measurements were carried out on the island of Ameland (The Netherlands) to determine whether notches cut into foredunes stimulated the supply of fresh calcareous beach and dune sand into the white and grey dune habitats behind the dunes, increasing these habitats' biological quality. Sediment characteristics and dynamics (deposition flux and grain size properties) as well as aspects of the vegetation (occurrence, composition and cover density) were studied along six transects, three behind an intact foredune and three behind a foredune with a notch cut into it. Compared to an intact foredune, the notched foredune exhibited higher deposition and accumulation behind the dune. The extra supply of sand was small, however, and for the notches studied, limited to the zone within approximately 50–60 m of the foredune's crest. Farther away from the dune, the effect of the notches became negligible. The presence of a notch did affect the grain size composition of sediment deposited behind the foredune. For intact foredunes, the grain size composition behind the dune was similar to that on the dune itself. When a notch had been cut, the sediment was finer behind the foredune, gradually coarsening away from the dune. Sand spray (deposition of sand eroded from the dune and transported in modified saltation during heavy winds) explains these granulometric results. The effect of the notches on the vegetation in the grey dune habitat behind the foredune was small and, for the notches studied, limited to the first approximately 35 m of the grey dune area, between 30 and 65 m from the foredune's crest. The notches had a greater effect on the white dune habitat but – in the opinion of the authors – this remained disproportionately small relative to the effort required for notch excavation and maintenance.