Australasian Hydrographic Society Education Award
It is with great pleasure that we announce the award of Aus$ 2500 for Academic Year 2006 to Philip James Dufty of the School of Biological, Earth and Environmental Sciences, University of New South Wales, to facilitate research for his Honours year. His Research Proposal is entitled ‘Bank Erosion and Vessel Wash on Estuarine Reaches of the Hawkesbury River, New South Wales’. As many readers will appreciate, this is research that will investigate a problem that is being experienced worldwide wherever rivers carry vessel traffic and their banks are constructed on a sedimentary base.
Erosion of the bank occurs through erosion of the toe and undercutting, leaving an overhang that then becomes unstable, fails and slumps down the riverbank. There are a variety of anthropogenic and natural circumstances that can cause this phenomenon, for example land clearing and high rainfall causing flooding, but this research is concerned with manmade erosion caused by vessel wash. Vessel-induced waves have a magnitude and erosivity controlled by the vessel's hull form, gross weight and speed all contributing to its draught and output of energy. The most damaging waves are created when the vessel is heavily laden, with maximal draught and travelling at low-to-critical speed. Whilst high speeds are quite popularly considered to be the most damaging, this is not the case when the speed is such that the vessel has a reduced draught through planing across the water surface. This is the case in many pleasure craft and specially designed high-speed river ferries; they create a more obvious wake but these waves are small, of shallow depth and less energy.
The upper reaches of the Hawkesbury River are ideal for this study as they flow through plains, which for the last decade have experienced markedly below average rainfall and also have flow regulation to conserve water; they are thus suffering no erosion from the flood factor. This facilitates the focus on vessel waves as the contributing factor of erosion. The sites selected for research have varying levels of vessel activity, both spatially and temporally, with observations being taken at an additional site which has no vessel traffic as a ‘no vessel’ control; all sites having similar bank morphology, tidal range, bank vegetation, aspect and fetch. The investigations will include differences in erosion rates according to vessel activity, rate differences resulting from bank material composition, rate differences for different positions on the bank if rates are greatest when previous erosion has already occurred and if point bars are sites of significant disturbance from vessel activity.
The research will consist of four main components. (1) Monitoring wash activity involving simple current/wave meters to obtain the overall level of wash activity as a function of vessel numbers and vessel activity. (2) Determination of bank erosion rates by survey using laser total station or optical level, a series of erosion pins inserted into the banks at field sites, which are related to accurately established benchmarks. (3) Sediment analysis wherein small quantities of sediment, typically less than 100gms, are extracted and subjected to detailed particle size analysis to determine the proportion of sand, silt and clay within the sediments. Where several stratigraphic elements are exposed in the banks a sample will be taken from each unit. (4) Depth of disturbance to determine the depth of activity with regard to erosion and deposition on a point bar from different levels of vessel activity during a full diurnal tidal cycle. The proposed methodology will look at erosion in relation to maximal, medial and minimal vessel activity, each aggregating a total of forty days intensive study. It is quite likely that this study may be continued on into the future.
Australia on the Map
A ‘400 years of Mapping Australia Conference’ is to be held in Darwin, Australia between 23rd and 25th August (inclusive) 2006. The conference and exhibition is part of AOTM celebration of Willem Janzoon's charting of 150 nautical miles of the east coast of the Gulf of Carpentaria in 1606, possibly the first European contact with Australia. The Australasian Hydrographic Society is strongly involved with this year of international celebration and encourages hydrographers, cartographers, historians, land surveyors and explorers and associated government agencies and private sector firms to fully support this conference. It is being organised by the Mapping Sciences Institute, Australia, the Institution of Surveyors, Australia, the Northern Territories Library and the Department of Planning & Infrastructure. For further information go to www.mappingsciences.org.au or e-mail menzies2@bigpond.net.au.
Contact
Australasian Hydrographic Society
Att. E. R. Whitmore
4/6 Carrington Street
Wahroonga, New South Wales
2076
Australia
Tel: +61 2 94892091
Fax: +61 2 94892048 |
