LONGSHORE SEDIMENT TRANSPORT DUE TO SEA BREEZES: AN IMPOUNDMENT STUDY

Abstract

The coastline of Perth, Western Australia, is subject to one of the strongest and most consistent sea breeze systems in the world. A significant feature of the sea breeze is that it blows obliquely-onshore and has a major impact on the incident wave climate and ensuing longshore sediment transport. Reviews of field data on longshore sediment transport have concluded that there are large uncertainties regarding the behaviour on low-wave energy, steep beaches. This study investigates the applicability of conventional equations to predict littoral drift rates on a site characterised by steep beach morphology, low-wave energy conditions and a bi-modal wave climate. Littoral drift rates were measured during an impoundment study, which involved monitoring the longshore transport rate by blocking sand movement with a permanent shorenormal groyne. Weekly surveys were conducted during a five-month period and these successive surveys provide data on changes in beach morphology and volume. The results are compared with three different predictions based on wave data and littoral drift equations (CERC and Inman and Bagnold (1963) equations). The longshore sediment transport is predicted well using the CERC equation when only considering the contribution of the wind waves. The sea breeze generated littoral drift is estimated 40,000–60,000 m. This investigation confirms that the sea breeze system plays and important role in determining the sediment budget in the region. INTRODUCTION The beaches along the coastline of Perth, Western Australia, are characterised by a steep gradient (5–6 ) and are subjected to low-wave energy conditions. The coastline is 1 Graduate Student, Geography Department, Loughborough University, Loughborough, LE11 3TU, UK. A.M.Tonk@lboro.ac.uk 2 Senior Lecturer, Geography Department, Loughborough University, Loughborough, LE11 3TU, UK. G.Masselink@lboro.ac.uk 3 Associate Professor, Centre for Water Research, University of Western Australia, Nedlands, WA 6907, Australia. Pattiara@cwr.uwa.edu.au