Leschenault Estuary (WA, 2010-2011)

Leschenault Estuary Modelling

The Leschenault Estuary lies to the north of Bunbury, in the south-west of Western Australia. The estuary is about 13.5 kilometres long, up to 2.5 kilometres wide, and has a surface area of approximately 25 square kilometres. It is shallow, with a mean basin depth of just 0.7 metres. Rivers flowing into the Leschenault Estuary,, including the Wellesley, Brunswick, Collie, Ferguson and Preston Rivers, drain a total catchment of 1981 square kilometres. The estuary is connected to the ocean at the southern end by a artificial channel known as “The Cut”, about 180 m wide, which was constructed in 1951 (MPRA, 2007). Concerns about the Leschenault Estuary include recent evidence of eutrophication in the form of extensive macroalgal blooms, and the perception that excessive sedimentation from ”The Cut” is filling the estuary far quicker than expected (MPRA, 2007).

The estuary has previously been the subject of considerable scientific enquiry (see Journal of the Royal Society of Western Australia, 83(4), 2000, http://www.rswa.org.au/). Charteris & Deeley (2000) developed a two-dimensional tidal model of the inlet and demonstrated that current speeds reached about 1.3 m s-1 through “The Cut” whilst the circulation in the northern part of the estuary was relatively weak. Their study was purely barotropic and did not include the effects of density gradients on the residual circulation and flushing of the estuary.

The West Australian Department of Water’s management of the Leschenault Estuary includes the development of numerical tools to assist in formulating and evaluating management strategies. The CEM is developing a hydrodynamic, model of the region, currently operating in near real-time. The model and the model outputs are described under the links on the left. The objectives of the study are to develop a calibrated hydrodynamic model of the estuary and its environs in order to quantify transport and residence times in the estuary so as to better understand the fate and impacts of nutrient loads.

References

Charteris, A. & Deeley, D.M. (2000). Hydrodynamics of Leschenault Inlet, Western Australia. Journal of the Royal Society of Western Australia, 83(4), 251-254.

MPRA (2007). The Leschenault Inlt/Estuary – A Changing Environment. Marine Parks & Reserves Authority, Government of Western Australia, 25 pp.

McKenna, Mike. & Western Australia. Dept. of Water (2007). The Leschenault estuarine system, South-Western Australia : condition statement and recommendations for management / [prepared by Mike McKenna] Dept. of Water, Bunbury, W.A., 180 pp.