Palaeodrainage at Uluru-Kata Tjuta National Park and implications for water resources.

Abstract

The stakeholders in the atypical rangeland area of Uluyu-Kata Tjufa National Park in the Northern Territory are the Aboriginal owners, hundreds of thousands of tourists, and vulnerable desert wildlife species. Sustainable water resources and maintenance of the integrity of the unique geological, ecological and cultural environment at Uluyu are major issues being addressed by the trustees of the Park. The Dune Plains area between Uluyu (Ayers Rock) and Kata Tjula (the Olgas) is the setting for a deep palaeovalley. The flat, dune-covered landscape of the present-day Dune Plains area provides no indication of the existence of the underlying palaeovalley. Integrated datasets including aeromagnetic and airborne gamma-ray spectrometric imagery, processed Landsat Thematic Mapper imagery, a digital elevation model, and water-bore logs, have enabled reconstruction of the Dune Plains palaeoriver valley. The datasets reveal a heterogeneous basement topography of domes and basins with 100 m of vertical relief (a buried 'mini-Kata Tjuia') at depth beneath the Dune Plains area, between the rock monoliths. The ancient valley became completely infilled with lake, river and wind-borne sediments during the Tertiary and Quaternary. Major faults traversing the basement beneath the area influenced early erosion and valley initiation. The palaeovalley was originally a closed valley which later evolved to a through-flowing river that fed Lake Amadeus to the north. The Dune Plains palaeovalley is now the setting for a compound bedrock- Cainozoic-sediment aquifer system which is the major source of water supply for the inhabitants and tourists of Uluyu-Kata Tjufa National Park. Major landscape units making up the Uluyu area include groundwater calcrete, sheetwash slopes of red earth, sandplains and dunefields, and modern ephemeral alluvial braidplains that are constrained to corridors afforded by swale networks. The sheetwash unit forms gently sloping aprons around outcrops and supports banded mulga shrubland. During rainfall, surface run-off acts as a 'sheetflow recharge mechanism'. This mechanism maximises water conservation allowing survival of the mulga groves and associated ecosystems. During major rainfall events, the sheetflow processes augment replenishment of the aquifer system at the base of the slopes. The palaeodrainage configuration and hydrodynamics of both the surface environment and the subsurface aquifer system are complex. The methodology used to reconstruct the Dune Plains palaeodrainage and associated aquifer system, and the hydrodynamic processes described for the Uluru area are applicable to widespread rangeland areas elsewhere across the continent. Keywords: Uluyu, Kata Tjula, Dune Plains, palaeovalley, palaeodrainage, hydrology, groundwater, aquifer, sheetwash, red earths, calcrete, hydrodynamics, mulga (Acacia aneura), run-off, run-on, recharge.