22.214.171.124.1 System boundaries and hydrostratigraphic units
The Maranoa-Balonne-Condamine subregion includes the following geological environments (from youngest to oldest) that contain individual groundwater systems:
- alluvial aquifers associated with major rivers (i.e. the Condamine, Balonne, Dumaresq and Macintyre rivers) and antecedent systems that form paleochannel infill and a broad alluvial cover over much of the subregion
- fractured rock aquifers within the Main Range Volcanics Formation
- sedimentary rocks of the geological Surat Basin that comprise aquifers of the Great Artesian Basin (GAB).
Most of the Maranoa-Balonne-Condamine subregion lies within the Murray–Darling Basin and the above-mentioned groundwater systems are included in the Commonwealth’s Basin Plan 2012 (developed under the Commonwealth’s Water Act 2007), with the exception of the GAB formations in the northern part of the Maranoa-Balonne-Condamine subregion. Under the Basin Plan, the Maranoa-Balonne-Condamine subregion includes ten groundwater sustainable diversion limit resource units that lie entirely within the subregion (Figure 20).
Figure 20 Groundwater sustainable diversion limit resource units for the Commonwealth's Basin Plan 2012, developed under the Commonwealth's Water Act 2007
Resource units that lie entirely within the subregion are in bold within the legend.
Throughout the subregion, groundwater is widely extracted for stock and domestic purposes, and to a lesser extent town water supply and intensive agriculture (e.g. feedlots). Groundwater extraction for irrigation is concentrated within alluvial aquifers flanking the upper reaches of the Condamine River, sections of the Macintyre and Dumaresq rivers, Macintyre Brook and north-west of St George. Aquifers of the GAB are a major water source for stock and domestic and town water supply purposes across the entire subregion. In addition, a significant amount of groundwater is extracted from the Walloon Coal Measures, within the GAB sequence, as a by-product of coal seam gas production.
126.96.36.199.2 Alluvial aquifer systems
Much of the subregion is covered, to varying extents, by an upper and lower alluvial system containing groundwater. The deeper system was previously referred to by the Murray‑Darling Basin Commission as the Gunnedah Subsystem (in NSW, this includes the Gunnedah Formation and underlying Cubbaroo Formation, although these are not widely recognised in Queensland). The deeper system is overlain by the more extensive Narrabri Subsystem (in NSW consisting of the Narrabri Formation, which again is not widely recognised in Queensland) (Barnett et al., 2004).
The extent of the Gunnedah Subsystem is poorly defined as a result of being obscured by the overlying Narrabri Subsystem (Skelt et al., 2004b). Within the Maranoa-Balonne-Condamine subregion much of the Gunnedah Subsystem is restricted to the southern part of the Border Rivers river basin, extending south into NSW between Mungindi and the south-eastern boundary of the subregion (to the west of Texas).
Kellett et al. (2006) reported a lower alluvial aquifer confined to a north-east to south-west buried paleochannel (the Dirranbandi paleochannel), roughly paralleling the Culgoa-Balonne rivers from north of St George to the NSW border.
The most productive alluvial groundwater systems in order of usage are located within the Condamine (Upper Condamine Alluvium), Maranoa-Balonne and Border Rivers river basins.
Condamine river basin
The Condamine Alluvium lies within a broad alluvial plain flanking the upper reaches of the Condamine River to the south-east of Chinchilla (Figure 24). The alluvium is on average between 20 and 30 m thick but thickens to 150 m south of Dalby (Hillier, 2010). The most productive groundwater area occurs in sand and gravel aquifers located in the central part of the area of mapped alluvium. No large groundwater reserves occur in the western area of mapped alluvium (Hillier, 2010). Skelt et al. (2004a) recognise alluvial aquifers within the area as part of the extensive Narrabri Subsystem that covers much of the subregion and extends into NSW. However, this designation is not universally accepted, and it has been suggested that the deeper alluvial aquifers may be equivalent to the Gunnedah Formation (which is included in the Gunnedah Subsystem by Skelt et al., 2004a).
Groundwater in the area has been used extensively for irrigation, industrial and stock and domestic purposes, with large-scale expansion first occurring in the 1960s. By 1970 it was recognised that the groundwater system was being over-exploited and an embargo on the issue of further groundwater extraction licences was introduced in the same year (Skelt et al., 2004a). Further, the Basin Plan has recognised this overuse and has set the sustainable diversion limit (SDL) less than the current use (baseline diversion limit (BDL)) (Table 9 and Table 10). Huxley (1982) reported that the aquifers of the Condamine Alluvium range from unconfined to semi-confined conditions and divided the alluvial sediments in to two groups based on depositional environment and hydraulic behaviour. The first group comprised sheetwash alluvium from adjacent weathered hard rock areas, consisting of predominantly clayey sediments, flanking the valley margins; the second group comprised sandier floodplain alluvium within the Condamine River Valley and tributary valleys deposited by the Condamine River and its antecedents. The two groups of alluvium are likely to intertongue, but the actual relationship is unknown (Huxley, 1982).
Border Rivers river basin
Within the Border Rivers river basin, groundwater exists within alluvial sediments associated with the Dumaresq and Macintyre rivers and Macintyre Brook. East of the confluence of the Macintyre Brook and the Dumaresq River, alluvial sediments are increasingly confined to narrow valleys. This contrasts with alluvial sediments to the west of the Dumaresq and Macintyre confluence, which are more extensive and are characteristic of an alluvial plain. Most water bores are located upstream of the Dumaresq and Macintyre confluence where fresh supplies are found, and these are dominantly used to irrigate lucerne and other fodder crops (Baskaran et al., 2009).
Both the Narrabri and Gunnedah formations are recognised within the area. The Gunnedah Formation is a fining upward sequence comprised of sands, gravels and clays up to 70 m thick (CSIRO, 2007). The Gunnedah Formation is overlain by the Narrabri Formation, which comprises sands, gravels and silts 10 to 30 m thick that form an unconfined aquifer (CSIRO, 2007). The topmost parts of the Gunnedah Formation consist of a 2 to 15 m thick semi-permeable clay sequence that separates the Narrabri Formation from underlying high permeability units.
Maranoa-Balonne river basin
Within the Maranoa-Balonne river basin, alluvial sediments associated with the Maranoa and Balonne rivers systems are widespread across much of the southern portion, reaching thicknesses of greater than 180 m (Exon, 1976). Both upper and lower alluvial aquifers are present, the latter only occurring in a small band in the south of the river basin. Most of the groundwater is saline; however, good quality water occurs in the vicinity of St George. The upper, coarse-grained, unconfined to semi-confined, alluvial aquifer system occurs extensively across much of the area. Aquifer thicknesses range from 20 m in the south-east adjacent to the Moonie River, to 60 m in the west (Kellett et al., 2006). The variable distribution of clay and sand within the upper alluvial aquifer is considered to result in a reduced vertical and horizontal hydraulic connection between sand beds when compared to the lower alluvial aquifer. The upper alluvial aquifer system has previously been referred to as the Narrabri Subsystem (Skelt et al., 2004b) and currently (for most of its extent) as the ‘St George Alluvium shallow’ groundwater sustainable diversion limit resource, under the Basin Plan. However, portions of the alluvial system in the north-east and north and south are within the ‘Sediments above the GAB: Condamine-Balonne’ groundwater sustainable diversion limit resource unit.
Underlying the upper alluvial system in the south of the river basin is a less extensive confining bed and lower alluvial aquifer system (referred to as the ‘St George Alluvium deep’ under the Basin Plan), which are restricted in distribution to the Dirranbandi paleochannel (Figure 23) (Kellett et al., 2006). Large thicknesses of Cenozoic alluvium in the Maranoa-Balonne river basin have only been encountered in this paleochannel.
The confining bed is considered to be leaky, consisting of 20 to 60 m of sediment dominated by clay and silt with minor sand beds in the lower part of the sequence.
The lower confined alluvial aquifer is higher yielding than the shallow alluvial aquifer and consists of a basal sequence of clay, silt and fine sand overlain by up to 20 m of coarse sand and gravel (Kellett et al., 2006). The aquifer thickness typically ranges between 20 and 40 m over much of its extent, increasing to 100 m at the depocentre of the Dirranbandi paleochannel (about 50 km south-west of St George).
Groundwater is extracted from the lower alluvial aquifer for irrigation and is concentrated in an area about 30 km north-west of St George. The distribution of bores within the upper alluvial aquifer is more widespread, and extracted groundwater is used mainly for stock and domestic purposes.
Moonie river basin
Little information is available regarding the shallow alluvial system (Narrabri Subsystem (MDBC, 2000)) within the Moonie river basin. Alluvial sediments are possibly up to 100 m thick with groundwater drawn from depths of between 10 and 35 m for stock and domestic use (CSIRO, 2008). A small portion of the St George Alluvium Shallow extends into the river basin.
Groundwater development in the Moonie river basin is low and widely distributed, and the surface – groundwater connectivity in the region is largely unknown (CSIRO, 2008).
188.8.131.52.3 Fractured rock aquifer systems
Condamine river basin
Within the Condamine river basin, significant but variable amounts of groundwater occur with the basalts of the Main Range Volcanics Formation (previously referred to as the Queensland Basalts (Barnett et al., 2004) and as the Upper Condamine Basalts in the Basin Plan). Located along the eastern margin of the Condamine river basin at depths of between 11 and 41 m, the aquifers generally consist of an upper unconfined weathered and fractured zone with a lower, more limited in extent, semi-confined fractured zone. Average aquifer thicknesses are in the order of 28 m (Skelt et al., 2004a). The basalts of the Main Range Volcanics Formation are covered in part with alluvium, including the Condamine Alluvium (QWC, 2012).
Groundwater is of excellent quality and is extracted for irrigation, stock and domestic use and town water supplies.
184.108.40.206.4 The Great Artesian Basin
The GAB is a variably confined groundwater basin comprising a multi-layered complex of sandstone aquifers (Figure 21). These aquifers are separated and confined by fine-grained mudstone and siltstone aquitards (Smerdon and Ransley, 2012).
The entire Maranoa-Balonne-Condamine subregion falls within the boundary of the geological Surat Basin which forms part of the wider GAB. To varying extents, the intake beds for the GAB outcrop over much the northern and eastern areas of the subregion – where alluvial cover is absent. In the northernmost extension of the region (north of Mitchell) the entire Mesozoic sequence of the GAB outcrops.
Groundwater bores intersecting the GAB are widespread within the subregion. Bores tapping the deeper aquifers of the GAB (i.e. Hutton and Precipice sandstones) tend to be located toward the shallower parts of the GAB, i.e. the north-western and eastern margins of the subregion. In contrast, bores tapping the shallower Cadna-owie – Hooray and equivalents aquifer are widely distributed across the entire subregion. Groundwater extraction is primarily for stock and domestic purposes, and town water supply.
Extraction of groundwater from the GAB aquifers has occurred since the late 1800s and has been historically elevated due to uncontrolled flow from artesian bores. Extraction has resulted in groundwater declines by up to tens of metres in some areas (Habermehl, 2002). The St George – Cunnamulla area has experienced the greatest decline in artesian pressure of anywhere in the GAB: over 100 m since development (Habermehl and Lau, 1997). This large drop in pressure has reversed vertical hydraulic gradients to the extent that in the St George area the hydraulic head in the Gubberamunda Sandstone is now 25 m lower than the head in the Mooga Sandstone.
The pressure decline in the St George area has been arrested since the Great Artesian Basin Sustainability Initiative was introduced in 1999. Under this initiative and earlier programs, 1287 bores had been controlled and 22,412, km of bore drains had been removed and replaced with 38,877 km of piped systems throughout the GAB at July 2013 (Great Artesian Basin Coordinating Committee, 2014). This reportedly resulted in an estimated water saving of 326,999 ML/year. The Queensland Department of Natural Resources and Mines (2005) reported in 2005 that water pressures had increased, resulting in an increase in hydraulic head of over 8 m in some bores in the St George – Cunnamulla area. However, it is noted that some areas have shown continued decline where hydraulic heads have not yet responded to reduced extraction (Macaulay et al., 2009).
The recent expansion of coal seam gas extraction from the Surat Basin in the east of the subregion has given rise to increasing volumes of co-produced groundwater extraction from the Walloon Coal Measures. The Walloon Coal Measures are considered an aquitard at a regional scale; however, more locally, some portions of the sequence act as an aquifer (QWC, 2012; Habermehl, 1980). The Walloon Coal Measures are laterally continuous with the Birkhead Formation of the Eromanga Basin, which occurs toward the western boundary of the subregion.
220.127.116.11.5 Hydrostratigraphic relationships
As of June 2012, an estimated 1400 coal seam gas wells (including wells that had produced water during the test phase) were reported as extracting water from the Walloon Coal Measures (QWC, 2012). Concerns surround the possible impact that large-scale extraction of groundwater from the Walloon Coal Measures may have on aquifers such as the Hutton, Springbok and Gubberamunda sandstones, as well as the Condamine Alluvium where it is in direct contact with the Walloon Coal Measures. Current management arrangements and future assessments of coal seam gas impacts in the Surat Basin are detailed in the Underground Water Impact Report for the Surat Cumulative Management Area (QWC, 2012).
Hydrostratigraphic relationships in the Maranoa-Balonne-Condamine subregion are presented in Figure 21, which indicates the temporal sequence of geological unit development and relative groundwater flow potential. The ‘Cenozoic aquifers and aquitards’ shown in Figure 21 represent the alluvial aquifers in the Maranoa-Balonne-Condamine subregion.
Figure 21 Hydrostratigraphic relationships in the Surat Basin, Coonamble Embayment and adjoining Eromanga Basin of the Great Artesian Basin
Source data: derived from data presented in Figure 4.4 in Ransley and Smerdon (2012) Recent geological mapping by the NSW Government has resulted in some changes to the stratigraphy in the Coonamble Embayment where the Griman Creek Formation has now been recognised as the topmost GAB formation.
18.104.22.168.6 Groundwater monitoring and assessment
Within the Maranoa-Balonne-Condamine subregion groundwater monitoring is undertaken by state water agencies for a variety of purposes including water level, water quality and salinity monitoring. Monitoring is focused on priority groundwater areas including the GAB, Condamine Alluvium, Border Rivers Alluvium, the St George Alluvium, and basalts of the Main Range Volcanics Formation. Within Queensland, water quality and water level data are collected by the Department of Natural Resources and Mines as part of the state’s Groundwater Ambient Water Quality Network and Groundwater Level Network to assist planning and management of groundwater resources. Water quality sampling frequency varies from one to three years and water level measurement frequency varies between two and four years depending on location (Department of Natural Resources & Mines, 2013a, b).
In addition, the Department of Natural Resources and Mines operates separate network monitoring water levels within the GAB in order to assess impacts of development and to gauge the effectiveness of management strategies such as the Great Artesian Basin Sustainability Initiative bore rehabilitation program.
Additional monitoring is undertaken by coal seam gas companies in parts of the Surat Basin. A cumulative management area has been established within the Surat Basin under the current Queensland regulatory framework, where monitoring aims to assess the cumulative impacts of coal seam gas activities on groundwater resources. Within the Surat Cumulative Management Area the Queensland Office of Groundwater Impact Assessment is responsible for assessing impacts and establishing integrated management arrangements in the Underground Water Impact Report for the Surat Cumulative Management Area (QWC, 2012). The Underground Water Impact Report obliges coal seam gas companies to undertake monitoring and in some cases construct new monitoring points, which contribute to:
- a regional monitoring network
- reporting of water pressure and quality
- reporting of water production data
- reporting of water quality and bottom hole pressures in selected coal seam gas wells (QWC, 2012).
In some cases coal seam gas companies may be required to undertake monitoring activities on lands other than those over which they hold tenure (QWC, 2012).
Increasingly, there is a requirement for mining companies, as part of mine approval conditions, to undertake local-scale monitoring and report unexpected groundwater level changes to the Department of Natural Resources and Mines.
New South Wales
The NSW Office of Water (2009) states that over 500 artesian bores in the NSW portion of the GAB Groundwater Source have been monitored for pressure, flow, temperature and groundwater quality. However, monitoring has been discontinued in many bores as they were decommissioned, became sub-artesian or were assessed as unsuitable for monitoring due to the condition of the borehead. The NSW Office of Water (2009) indicated that 60 of these GAB bores were being monitored at least once every two years.
No non-GAB bores are monitored within the NSW portion of the Maranoa-Balonne-Condamine subregion.
Figure 22 Distribution of Queensland and NSW groundwater monitoring bores in the National Groundwater Information System database
Source data: Bureau of Meteorology (2013) ‘Great Artesian Basin’ monitoring bores are those locations where groundwater is actively monitored in the GAB; the remaining groundwater wells may be installed in any of a number of groundwater systems (including the GAB).
Product Finalisation date
- 1.1.1 Bioregion
- 1.1.2 Geography
- 1.1.3 Geology
- 1.1.4 Hydrogeology and groundwater quality
- 1.1.5 Surface water hydrology and water quality
- 1.1.6 Surface water – groundwater interactions
- 1.1.7 Ecology
- Contributors to the Technical Programme
- About this technical product