Influence of basalt flows and alluvial deposition on surface and groundwater hydrology on the Great Divide, North Queensland

Whitehead, P.W., and Nelson, P.N. (2008) Influence of basalt flows and alluvial deposition on surface and groundwater hydrology on the Great Divide, North Queensland. In: Papers from 2008 Western Pacific Geophysics Meeting. From: American Geophysical Union, Western Pacific Meeting, 29 July – 1 August 2008, Cairns, QLD, Australia.

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Abstract

Saline groundwater poses problems in parts of the irrigation area that straddles the Great Divide near Mareeba, north Queensland. In some places the watertable has been rising rapidly, leading us to examine aquifer geology to determine why. Two study sites were chosen, both being relatively flat areas where the catchments of the Mitchell River (which flows in to the Gulf of Carpentaria) and Barron River (which flows into the Coral Sea) adjoin. Aquifer geology was examined using aerial magnetic survey data, drilling records from existing bores, on-ground magnetic surveys, drilling and other on-ground observations. At the first study site, in Cattle Creek catchment (sub-catchment of the Mitchell River) east of Mareeba, basalt flows approximately 10 m thick and several 100 m wide were found, buried under 7 m of alluvium. The basalt flows cut across from Granite Creek catchment (sub- catchment of the Barron River) into Cattle Creek catchment. The continental divide in this region has therefore migrated west since the eruption of the basalt, 1.79 million years ago. A rapid rate of watertable rise in Cattle Creek has previously been attributed to high recharge from within the catchment. However groundwater flow may be following the trend of the sub-surface strata, rather than reflecting the surface drainage divides. The rising watertable levels in the Cattle Creek catchment may therefore be influenced by groundwater flows from the adjacent Granite Creek catchment. At the second study site, north of Mareeba, buried basalt flows also occur along the continental divide between Mitchell River and Barron River. Borehole data, combined with accurate surveying of bedrock in the present river channel, showed that the paleo-channel down which the lava flowed must have been a tributary of Mitchell River. The major tributaries of this blocked channel were diverted to the east to become the headwaters of Barron River, resulting in the western migration of the continental divide. The consequent reduction in stream energy available to the truncated headwaters of Mitchell River has led to channel infill and aggradation of more than 30 m since the diversion of the Barron River. In regions where surface gradients are low, catchment area management may need to consider the practices operating in adjacent catchments.

Item ID: 8329
Item Type: Conference Item (Presentation)
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Date Deposited: 09 Mar 2010 03:08
FoR Codes: 04 EARTH SCIENCES > 0406 Physical Geography and Environmental Geoscience > 040603 Hydrogeology @ 50%
04 EARTH SCIENCES > 0406 Physical Geography and Environmental Geoscience > 040607 Surface Processes @ 50%
SEO Codes: 96 ENVIRONMENT > 9609 Land and Water Management > 960905 Farmland, Arable Cropland and Permanent Cropland Water Management @ 100%
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