Evolution of beach profiles under random waves

Evolution of beach profiles under random waves

Janssen, C.M.

d' Angremond, K. (mentor)
Bezuyen, K. (mentor)
De Graaf, G. (mentor)
Holmes, P. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

River, Estuary and Coastal Engineering

1993-10-01

Cross-shore sediment transport is an important phenomenon in coastal engineering, which mainly accounts for the short-term changes in the coastline. To study on- and offshore transport the evolution of the beach profile is considered. For investigation of the beach profile small-scale physical models are often used. A problem in using a physical model is the introduetion of scale-effects resulting from the impossibility of sealing all parameters correctly. Many researchers therefore derived sealing laws which determine the relationship between the model scale and the seale of the other parameters. A literature review revealed that many of them give contradictionary results. A different problem in using physical models is that for small-scale models the required model grain diameter of the sediment becomes too small, which would introduce cohesive forces in the sediment. For this reason light-weight material is sometimes used as the beach material. However there are still doubts about the validity of the use of light-weight material. In order to study the behaviour of light-weight material in physical models, experiments were performed using random waves in the large wave tank of the Hydraulics Laboratory. Both sand and anthracite were used as the model materials. Although all the resulting beach profiles showed accretive conditions, characterized by the development of a berm at the beach and the deepening of a step in the breaker zone, differences between the profiles in the anthracite and sand models were very large. Beach profiles were analyzed using different methods. The eigenfunction analysis turned out to be helpful only for the analysis of field data. In the other methods the relation between the characteristic features of the profile and the parameter H/wT was investigated. This parameter is assumed to be a criterion to differentiate between on- and offshore transport and represents the wave conditions and sediment characteristics for the evolution of the beach profile. In general the relation was rather poor and there is clearly a need for further theoretical and model studies.

sediment transport
coastal engineering
beach profile

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Student theses

master thesis

(c) 1993 Janssen, C.M.