Gradient in Longshore Transport of Sediment in UNIBEST-TC

Gradient in Longshore Transport of Sediment in UNIBEST-TC

Veuger, A.

d'Angremond, K. (mentor)
Van de Graaff, J. (mentor)
Roelvink, J.A. (mentor)
Boers, M. (mentor)
Klopman, G. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2001-06-01

The area of interest in this study is the closed part of the Holland coast. This is the coastal stretch from Den Helder to Hoek van Holland. Here the coast is not interrupted by tidal inlets like at the Waddeneilanden or Zeeland.Due to erosion and accretion the coast is not always stable. Many investigations have been done on these phenomena throughout the years.Programs to predict morphological changes along a granular coast are developed by several countries. In the Netherlands Delft Hydraulics developed the cross-shore profile model UNIBEST-TC. The program considers uniform longshore transport of sediment and does not incorporate the option of inserting a gradient in longshore transport of sediment. In reality this gradient in longshore transport of sediment will often occur and it can be of considerable importance to certain coastal developments. In a recent extension of the program, which is still on a experimental basis, the option to incorporate this gradient was included. In this study the effect of a gradient in wave driven longshore transport of sediment on the shape of the cross-shore profile was investigated. It was also investigated whether an inclusion of a gradient in longshore transport of sediment in the program UNIBEST-TC leads to a better simulation of the measured bottom evolution at eroding and accreting profiles. Furthermore it was investigated whether the differences in large scale coastal behaviour at the different regions along the Dutch coast can be explained by a gradient in longshore transport of sediment. It showed that, with an eroding gradient in longshore transport of sediment included in the program UNIBEST-TC, the profile becomes more steep in the breaker zone and the bar height and offshore migration speed of the bars is decreased. With an accreting gradient in longshore transport of sediment the opposite occurs: the profile becomes less steep in the breaker zone and the bar height and offshore migration speed ofthe bars is increased. Stable, eroding and accreting profiles along the closed part of the Holland coast were recognised using the JARKUS-data and the extended measurements. For several profiles along the coast simulations were made with and without the gradient included. It was tried to establish one model-setting for all profiles along the Dutch coast, to get a clear view of the effect of the gradient. This last showed to be very difficult or even impossible, which is probably caused by either difficulties in the simulation of the differences in cross-shore transport between the different regions alongshore or due to other phenomena not taken into account in the program UNIBEST-TC. From the analysis on the profile volume and profile steepness in this study, it was found that the inclusion of the gradient in longshore transport of sediment in UNIBEST-TC has a positive effect on the simulation of the development of the general profile shape of eroding and accreting profiles. Also the accretion near the shoreline, caused by cross-shore import of sediment from the deeper parts of the profile, with a profile indicated as stable from the measurements, can be reduced using an eroding gradient. Because of the limited time for this study only a few profiles along the Dutch coast were observed. It was found that from this limited amount of investigated profiles no real conclusions can be drawn concerning the question whether the differences in large scale coastal behaviour at the different regions alongshore can be explained by a gradient in longshore transport of sediment. Only a few assumption were made. A thorough investigation on this subject could be made in a future study. In this study also a method to calculate the gradient in longshore transport of sediment was developed. Though in the calculation of the gradient some simplifications were made, the results are satisfactory.

sediment transport
coastal morphology

http://resolver.tudelft.nl/uuid:f142a761-eab8-4c32-a246-8bffacbc5697

Student theses

master thesis

(c) 2001 A. Veuger