Spatial variability of aeolian sand transport rates in a foredune notch Thesis
- Author
- Hammecher, L.
- Year
- 2023
- Publisher / Organisation
- Univeristy of Utrecht
- Pages
- 23
- Summary
- After decades in which the dominant coastal management strategy in the Netherlands consisted of planting of vegetation to suppress dune dynamics, nowadays dune management projects intent to restore natural dynamics. The fixed foredunes resulting from the previous management strategy act as an almost complete barrier to aeolian transport from the beach towards the back dunes. This has resulted in a decline in biodiversity. Additionally, this has prevented dunes from growing vertically with the rising sea level. New forms of management strive to prevent further loss of biodiversity, and stimulate the vertical growth of dunes. At multiple locations, management projects have consisted of the excavation of foredune notches. That has been done to simulate natural blowouts, in which winds are able to freely transport beach sediments through the dune towards the hinterland. Previous research has focused on wind flow patterns in excavated notches, but the spatial variability in aeolian sediment transport is yet unknown. To study this variability, measurements were carried out in a foredune notch at Bloemendaal aan Zee, in October-November 2022. Additionally, the relation to wind speed and direction was studied, as well as the effects on the morphology. This was done using sand catchers, ultrasonic anemometers and RTK-GPS surveys. Thisstudy shows that the spatial variability of sand flux through the notch is dependent on the offshore wind direction and the local morphology. Sand fluxes in the notch varied between 1.02 and 177.72 g m-1 s -1 , and the highest fluxes were measured on the landward side of the deflation basin. With increasing oblique approaching winds, the sediment flux in the notch increased landward, while notch axis-parallel winds resulted in decreased transport through the notch. This pattern is caused by topographical steering, and the fact that oblique approaching winds tend to accelerate within the notch, gaining more potential to transport sediment. The local morphology steers the local wind direction, creating the observed sand transport patterns within the notch.