The presence of Neogene fault systems can have a significant impact on hydraulic connectivity of aquifers, juxtaposing otherwise disconnected aquifers, enhancing recharge and/or discharge or acting as barriers to flow and consequently compartmentalising groundwater resources. Previously, regional airborne electromagnetics (AEM) transects allied with groundwater investigations have pointed to the potential for localised compartmentalisation of the Daly River Basin groundwater systems. However, existing data is sparse, and equivocal.In this context, the main aim of the Daly River Basin Project is to determine if compartmentalisation of the aquifers is a significant factor and thus should be explicitly considered in groundwater modelling and water allocation planning. The objectives of the project main goals of the project are to: (1) map Neogene faults through the use of airborne electromagnetic (AEM) and morphotectonic mapping, and (2) assess the permeability and transmissivity of mapped fault zones and their role in potential groundwater system compartmentalisation. Data acquisition includes 3325 line-kilometres of new AEM and airborne magnetics, ground (ground magnetic resonance (GMR)), and borehole geophysics, drilling, groundwater sampling and hydrochemical analysis, geomorphic and morphotectonics mapping. Hydrogeophysical, geomorphic and hydrogeological data will also be used to better understand groundwater-surface water connectivity and the potential for managed aquifer recharge schemes to replenish extracted groundwater resources. The outcomes of this project will inform decisions on water allocations and underpin effective and efficient groundwater use. This paper specifically reports on the ability of AEM and morphotectonics mapping to identify Neogene fault systems in the Daly River Basin.
Abstract Environmental radiocarbon was used to study aspects of groundwater origin, transport and mixing in the aquifer system underlying northern Victoria. The clearing of native vegetation and the advent of irrigation on the northern plains have upset the hydrological balance, caused water tables to rise and in some areas caused the waterlogging and salination of the land. Groundwater shallower than 30 m only yielded modern radiometric dates. Groundwater in the ‘Calivil/Renmark Aquifer’ in the Loddon and Goulburn Valleys has yielded ages up to 20 000 years and has a flow rate between 0.13 and 0.01 m day‐1. These values agree with the mean pore velocity calculated using Darcy's Law.
A local succession of interbedded dolostone, limestone and glauconitic sandstone in the central Daly Basin of the Northern Territory, dated as Early Ordovician, has for many years appeared incongruous in terms of lithology and age relative to mapped formations of the Cambrian Daly River Group. Geological mapping and stratigraphic drilling have now shown that this interval, recently named the Florina Formation and described here, unconformably overlies the karstified surface of the uppermost formation of the Daly River Group, the Oolloo Dolostone. It is the youngest formation of the Daly Basin succession, but due to the lengthy hiatus between it and the underlying units, it is not included within the Daly River Group. It comprises three intervals of carbonate rocks alternating with thicker intervals of siliciclastic rocks. The latter are viewed as forming under dominantly moderate energy, shallow marine conditions with sediments derived from a distant terrigenous source. The carbonate rocks were dominantly subtidal, too far offshore to receive significant amounts of terrigenous material but shallow enough to be above storm wave base. The Oolloo Dolostone is formally divided here into two members, the lower Briggs Member and the upper King Member. Both consist largely of dolostone, but the Briggs Member is typically well bedded, contains ooids and has a minor component of quartz sand. It accumulated mainly as ooid shoals seaward of tidal flats. The overlying King Member is massive to coarsely bedded with only traces of terrigenous sediment and was deposited in deeper water seaward of the Briggs Member.
The Western Australia (WA) and Northern Territory (NT) Governments proposed an area adjacent to the Ord River Irrigation Area for irrigation development. The Natural Resource Agencies of the two Governments determined that development would only be authorised once the existing water resource conditions were known, and when the proponent had shown that irrigation could be managed to preserve natural streamflows and operate sustainably. To enable the hydrogeological conditions to be determined and modelled, an airborne electromagnetic survey was commissioned. Each of the hydrogeological environments was evaluated to determine the effects of irrigation and land-use changes on groundwater levels, groundwater quality, and on flows in seasonal watercourses.The results of two generations of groundwater modelling were integrated in the environmental management plan for the irrigation project, with requirements for continuous monitoring and interactive groundwater modelling to be specified throughout the life of the irrigation project. This is an innovative application of geophysics, where the full life cycle of irrigation could be planned and water use managed, based on environments identified in an airborne survey.
Abstract The Mataranka Springs Complex is the headwater of the iconic Roper River of northern Australia. Using environmental tracers measured in springs and nearby boreholes, the origin of groundwater contributing to the springs was evaluated to help assess the impact of proposed groundwater extraction in the Cambrian Limestone Aquifer (CLA) for irrigation agriculture and for hydraulic fracturing in the Beetaloo Sub-basin (an anticipated world-class unconventional gas reserve). Major ions, Sr, 87 Sr/ 86 Sr, δ 18 O-H 2 O, δ 2 H-H 2 O, 3 H, 14 C-DIC were consistent with regional groundwater from the Daly and Georgina basins of the CLA as the sources of water sustaining the major springs (Rainbow and Bitter) and one of the minor springs (Warloch Pond). However, 3 H = 0.34 TU in another minor spring (Fig Tree) indicated an additional contribution from a young (probably local) source. High concentrations of radiogenic 4 He (> 10 –7 cm 3 STP g –1 ) at Rainbow Spring, Bitter Spring and in nearby groundwater also indicated an input of deeper, older groundwater. The presence of older groundwater within the CLA demonstrates the need for an appropriate baseline characterisation of the vertical exchange of groundwater in Beetaloo Sub-basin ahead of unconventional gas resource development.
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