Directional Waves in the Nearshore Coastal Region of Perth ...

Directional waves in the nearshore coastal region of Perth, Western AustraliaHuey Jean TanABSTRACTThe conventional approach for wave analysis is the relatively simple monochromatic waveapproach, which is still widely used in coastal and offshore applications. This traditionalmethod does not consider the direction of wave propagation, which is an important factor toconsider in order to realistically characterise the natural surface waves of the ocean.Directional wave methods are more complex, time consuming and expensive than theconventional monochromatic wave approach. However, it has been proven that directionalwave analysis offers a more accurate representation of natural ocean waves, and that there aresignificant differences between the transformations of monochromatic and directional waves.Directional waves in the nearshore coastal region influence the direction of littoral drift on thebeach, which, in turn, affects the morphology on the beach. The beaches along the coastlineof Perth, Western Australia, exhibit seasonal variations in beach morphology. The main aimof the present study was to carry out an analysis of the directional waves in the nearshoreregion of the coastal waters of Perth. This was achieved by analysing the directional wavedata collected at Cables Artificial Surfing Reef (ASR) in August 1999 (i.e. winter) and at CityBeach during January and February 2001 (i.e. summer). More specifically, due to the fact thatwave growth and the direction of wave propagation are directly affected by wind, this studyinvestigated the wave response to the changing wind climate. The summer data (i.e. at CityBeach) indicated that the propagation of nearshore waves were predominantly in the northeastdirection, whereas the winter data (i.e. at Cables ASR) displayed directional waves in apredominant east-southeast direction. This is in agreement with the observations by Masselink& Pattiaratchi (2001) of the prevailing northward sediment transport during the summermonths and southward longshore transport during the winter months. Swell waves duringsummer is predominantly in the east-northeast direction, whereas the dominant swell directionin winter is east-southeast. The daily sea breeze events during summer generate sea waves inthe northeasterly direction. Sea waves generated by storm events change from southeasterly tonortheasterly with the passage of mid-latitude depressions, however the direction of swellwaves remain constant in the east-southeasterly direction. During the summer samplingperiod, the mean significant wave height (H s ) was 0.77 m, and the maximum H s achievedduring a sea breeze event was 1.33 m. For the winter sampling period, the mean H s was 1.17Abstracti