A reanalysis of the wave observations in Lake George

A reanalysis of the wave observations in Lake George

Breugem, A.

Stelling, G.S. (mentor)
Holthuijsen, L.H. (mentor)
Zijlema, M. (mentor)
Zitman, T.J. (mentor)

Civil Engineering and Geosciences

2003-05

The wave growth experiment in the Australian Lake George (Young and Verhagen, 1996a) is the first multiple-station depth-limited wave growth experiment and the dataset is probably the best that is available. The lake has a horizontal flat bottom with a depth of about 2 meters and is orientated north-south. There are however some discrepancies in the wave growth data that were observed. The development of the waves differed significantly between northern- and southern-wind cases and to a lesser extent between day and night. In addition, the significant wave height decreases with an increasing fetch after a certain distance. These anomalies may have a significant influence on the coefficients of the wave growth expressions that were determined by Young and Verhagen (1996a). Therefore, the objective of the present study is to determine the cause of these anomalies and to investigate their influence on the wave growth expressions. Simulations with the SWAN wave model, in a version that uses the RIAM technique to solve the quadruplet wave-wave interactions show that the differences in the wave growth between northern and southern are caused by the lateral coastline over the first half of the lake. The observed wave growth during northern-wind is very much comparable to the idealized situation of wave growth in a one-dimensional situation with a straight coastline perpendicular to the wind direction. In southern-wind conditions, the wave growth over the first half of the lake is significantly slower. In addition, the recorded spectra in the first stations during southern-wind are anomalous. It was found that the decrease of the wave height in the second part of the lake is greater during northern-wind than during southern-wind. The decrease during northern-wind is much stronger during the night than during the day. The cause for this decrease of the wave height had not been found in the present study. There are however some indications that the shape of the lateral coastline are (at least partly) responsible, but that whitecapping and quadruplet wave-wave interactions mask this behavior. There may also be some secondary influences of atmospheric stability (stronger decrease in unstable conditions). The shape and location of the coastline in Lake George have a strong influence on the directional properties of the two-dimensional wave spectra. The wave model shows two peaks in the directional wave spectra at some measurement stations and in case of slanting wind conditions, the model shows that the waves tend to align to the main direction of the lake, rather than to the wind direction. New coefficients for the wave growth expressions are proposed here, based on the northern-wind cases as these cases seem to be fairly free from the influence of the lateral coastline. In addition, the influence of the decrease in the significant wave height is ignored explicitly

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TU Delft, Faculty of Civil Engineering and Geosciences, Hydraulic Engineering

Student theses

master thesis

(c) 2003 A. Breugem