Townley, L.R., and Fleming, P.M. (1993). Hydrologic overview of the Shoalwater Bay region - with special emphasis on the eastern dune fields. Report to the Commonwealth Commission of Inquiry, Shoalwater Bay, Capricornia Coast, Queensland. CSIRO Division of Water Resources, Consultancy Report 93/30, 86pp., October 1993.
A review is provided of existing data on the hydrology and hydrogeology of the Shoalwater Bay region generally, and the eastern dune fields of the Shoalwater Bay Training Area (SWBTA) in particular. The review covers the climate, landforms, vegetation, surface hydrology and hydrogeology of the region, and includes some comments on the reliability of the data. There is a significant lack of detailed information about the hydrogeology of the region. In particular, the elevation and physical properties of the basement below the dune fields are unknown. There is also a lack of information about indurated layers within the sand mass, and their relationships with apparently perched lakes and sinkholes.
Based on the available data, a conceptual model of the hydrology of the eastern dune fields of the SWBTA is presented. The model focuses on the catchment of the northern Sandy Creek, which provides important base flow for the water supply of Livingstone Shire on the Capricornia Coast. The catchment has two distinct regions: a relatively flat region which provides storm runoff during and shortly after rainfall events, and a portion of the eastern dune fields, from which groundwater outflow provides base flow throughout the year.
Possible effects of sand mining are discussed in the context of the conceptual hydrological model, in order to identify questions which can not be answered or which can only be answered with uncertainty. A mathematical model is used to support the argument that if mining causes an increase in hydraulic conductivity below the regional water table and if mining were to occur near the inland end of the dune fields, base flow would tend to increase slightly, rather than decrease. There would also be a tendency for seasonal fluctuations in base flow to decrease, such that base flows in the dry season would be marginally higher than before mining. Both effects are probably negligibly small, if not undetectable, because of the small size of mined areas relative to the contributing area of the sand mass, and because of normal climatic and hydrological variability. Mining too close to perched lakes would certainly destroy those lakes. Accidental spillages of fuels, oils or other chemicals, either through mining or military activities, could adversely affect water quality in the northern Sandy Creek. The effect of mining in the Dismal Sector would have a negligible effect on groundwater outflows to Port Clinton and the Coral Sea, and in particular, an infinitesimal effect on the salinity in those water bodies.
A program of research is suggested to allow the development of a descriptive model of the hydrology and hydrogeology of the eastern dune fields of the SWBTA, capable of assessing potential impacts of proposed sand mining on the existing and future water supply for the Livingstone Shire, and on the interrelationship between salt water and fresh water in Port Clinton and along the coast of the Coral Sea. Further confidence about a number of hydrological and hydrogeological issues could be obtained by a fairly brief field investigation. A detailed model of the region will only be possible after extensive drilling and/or geophysical investigations, and a period of monitoring of groundwater levels.
Copyright © 2005 by Lloyd Townley