Extension of a Cross-Shore Beach Profile Model for Coarse Materials and Steep Slopes

Date of Award

Spring 2004

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil & Environmental Engineering

Program/Concentration

Civil Engineering

Committee Director

David R. Basco

Committee Member

A. Osman Akan

Committee Member

George F. Oertel

Call Number for Print

Special Collections LD4331.E54 H28 2004

Abstract

In the present SBEACH model, the effective grain size can range from 0.13 to 1.0 mm. The grain size greatly influences three main processes of the model: fall velocity, sediment transport direction, and sediment transport rate. First, the theory of the fall velocity, which is called Hallermeier's formula in the SPM (1984), is replaced by the new theory in the CEM (2002). Second, the sediment transport direction is changed by two criteria. One was developed by Sunamura and Horikawa (1974). This theory includes the beach slope. The other was derived by Ahrens and Hands (2000). The effective grain size range is between 0.0625 and 30 mm. Finally, we assume that there is a similar trend between the cross-shore sediment transport rate and longshore sediment transport rate if the grain size becomes bigger. Based on this hypothesis, the cross-shore sediment transport rate coefficient is estimated for coarse sand by using two longshore sediment transport theories. Several modules in the original model were modified, based on the above theories. In this study, the modified model is called SBEACHX.

Model tests are performed under simple initial information to investigate the influence of the modules in SBEACHX if the grain size becomes large. The results are analyzed in terms of fall velocity, sediment transport direction, sediment transport rate, wave height, and wave period. It is found that as the grain size becomes larger, the sediment transport rate becomes smaller.

The efficiency of SBEACHX is investigated by comparing the results from SBEACHX with measurements from HR Wallingford, UK, and from the Public Works Research Institute (PWRI), the Ministry of Construction, Japan. However, SBEACH and SBEACHX could not reproduce beach profile change starting with the same initial beach profile and input wave conditions as the experiments. By analyzing the results, three reasons can be considered. The first reason is that the storm wave conditions in the laboratory experiments are not strong enough to move the sediment in SBEACH. The second reason is that there is a limitation of slope in the sediment transport model. The third reason is that the algorithm of the sediment transport for the swash zone in SBEACH is not appropriate for coarse materials and steep beaches. Also, the sediment transport direction theory in SBEACH cannot predict the correct direction from the Japanese experiment.

Finally, it is concluded that the modified model developed in this study cannot predict beach profile change with coarse material. For future work, more full-scale experiments with coarse materials and steep slopes under proper storm conditions for SBEACH are recommended to investigate the sediment transport model with considering coarse materials and steep slopes.

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DOI

10.25777/5hvy-w425

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