Coastal Aeolian Sediment Transport in an Active Bed Surface Layer

Coastal Aeolian Sediment Transport in an Active Bed Surface Layer: Tracer Study and Conceptual Model

Uphues, Charlotte (TU Delft Civil Engineering and Geosciences)

de Vries, S. (mentor)
van IJzendoorn, C.O. (mentor)
van Prooijen, Bram (mentor)
Pearson, S.G. (mentor)
Hallin, E.C. (mentor)
Miot da Silva, G. (mentor)

Delft University of Technology

Civil Engineering | Hydraulic Engineering

2021-10-07

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.

Aeolian sediment transport
Supply limited
Sediment sorting
Armoring
Aeolian ripples
Tracers
Field measurements
Conceptual model
Beach

http://resolver.tudelft.nl/uuid:11fc3463-9bea-4638-b782-169abe398934

2022-10-07

52.25556,4.43611

The main body of this thesis (Part I: Paper) is provided in paper format with the aim to publish it in the Special Issue in Earth Surface Processes and Landforms “Coastal dunes: links between aeolian processes and landform dynamics”. Therefore, the Embargo option with end date October, 7 2022 (1 year after graduation) is chosen.

Student theses

master thesis

© 2021 Charlotte Uphues