1.1.4.3 Groundwater flow

Groundwater flow in the pre-Cenozoic aquifers of the Clarence-Moreton bioregion is divided into a westerly and easterly flow component. The groundwater divide between an easterly and westerly flow direction (and thus, the eastern boundary of the Great Artesian Basin) is believed to be the Helidon Ridge (Smerdon et al., 2012), located near the western boundary of the Laidley Sub-basin. However, the exact orientation of this groundwater divide is at present poorly constrained due to insufficient monitoring bores. In addition, the location of the groundwater divide is likely to be different for different aquifers. Generally, flow in the alluvial aquifers follows that of the associated creeks and rivers with water levels responding to recharge, pumping and irrigation stresses. A few groundwater flow models have been built for the Lockyer Valley alluvial aquifer system in recent years. A detailed analysis of the groundwater flow in the Richmond River alluvial aquifer is presented in Drury (1982).

Vertical hydraulic relationships between shallow and deep aquifers or between different bedrock aquifers are poorly constrained throughout much of the Clarence-Moreton bioregion. However, where sufficient groundwater chemistry and water level are available (e.g. Lockyer Valley and Bremer/Warrill river basins), it is possible to infer hydraulic relationships between alluvial and bedrock aquifers. For example, groundwater chemistry and water level data show that the alluvial aquifer systems are strongly connected to the basalts of the Main Range Volcanics in the upper reaches of the river basins in south-east Queensland and north-east New South Wales. Further down gradient, where the alluvial aquifer systems commonly overlie Clarence-Moreton bioregion sedimentary sequences, the nature of the connectivity between alluvium and bedrock is more variable, both spatially and temporally. The high salinities of alluvial groundwater in some areas confirm that there is mixing of water between the alluvial and Clarence-Moreton Basin aquifers. However, elsewhere, distinct water chemistry and groundwater levels suggest that there is only limited connectivity.

1.1.4.3.1 Groundwater levels and yields

Groundwater levels in the unconfined to semi-confined alluvial aquifers range from 10 to 30 m, and are heavily influenced by recharge from excess rainfall and groundwater extraction for irrigation. Under the current management and climatic conditions, the Lockyer Valley alluvial aquifer remains under stress, and the groundwater resources there are exploited beyond their sustainable yields with pumping often continued until bore yields significantly decline, however, groundwater levels partially recover during high rainfall years. Since the 1970s, the majority of the monitoring bores in the Lockyer Creek basin have shown a net fall in groundwater level ranging from 5 to 15 m (Hair, 2007). A number of different studies have been undertaken to quantify the groundwater resources of Lockyer Valley alluvial aquifer (Durick and Bleakley, 2000; Hair, 2007; Chee et al., 2012; Bleakley and Boreel, 2012a, 2012b, 2012c; Wolf et al., 2012). Similar trends have been observed in the Bremer/Warrill alluvium since the 1960s with more significant declines since 1992. However, the break of drought in 2008 and the flooding of 2011 have resulted in a very significant recovery of groundwater levels in the Lockyer Valley and other river basins in south-east Queensland, with water levels often recovering to the pre-drought levels of the early 1990s.

In the Clarence area, the Richmond River alluvium also has shallow watertables. They have bore yields in the range 0.5 to 1.0 L/second. These unconfined to semi-confined aquifers have medium to high permeability and are replenished by the recharge from excess rainfall (Brodie, 2007). Groundwater levels in the Richmond and Clarence alluvial and coastal areas are of particular importance because of the presence of acid sulfate soils combined with drainage activities on a large scale. Acid sulfate soils are found underlying coastal flood plains and wetlands in the Richmond and Clarence river basins in New South Wales (locations reported in Section 1.1.2). Maintaining acid sulfate soils in a fully saturated state is the key to keeping them stable with drainage exposing the pyrites, which upon exposure to oxygen and oxidation, will generate acid. Johnston et al. (2004) concluded that the acidity of drainage water was highly sensitive to the hydraulic gradient between the groundwater table and the adjacent drain water level with most seepage occurring while the back swamp groundwater table being within a narrow elevation range, referred to as an ‘acid export window’. Land and Water Management Plans have been developed by the relevant councils with a primary focus on managing the impacts of acid sulfate soils. For instance, the plan developed by the Richmond River County Council has established a requirement for managing acidic and potentially acidic soils underlain by an artificially lowered watertable.

The Cenozoic Basalt aquifer in the Alstonville Plateau in the New South Wales part of Clarence-Moreton bioregion has productive areas within the 20 to 100 m depth range with yields ranging from 0.5 to 1.5 L/second. Despite the low to medium yielding nature of these basalt aquifers, high yields of up to 30 L/second have been reported at shallow depths.

In the pre-Cenozoic Clarence-Moreton bioregion aquifers in Queensland, the groundwater potentiometric contours show that groundwater levels and flows generally follow the topographic gradients (Pearce et al., 2007a, 2007b). For the pre-Cenozoic formations of the Clarence-Moreton bioregion, availability of groundwater level data is rather sparse both spatially and temporally. Groundwater level data for the Clarence-Moreton bioregion aquifers are available for much of the Lockyer Valley and in the Bremer/Warrill/Purka river/creek basins. The details of this are available in the corresponding hydrogeological investigations reports for these basins (Pearce et al., 2007a, 2007b, DNRM, 2005) as well as in the groundwater database (Department of Natural Resources and Mines, 2013). However, the spatial and temporal resolution of the basin’s groundwater level data is not adequate to support a long-term trend analysis, and in particular, there is a lack of nested bore sites where different basin aquifers are monitored at the same site in order to determine vertical relationships.

The pre-Cenozoic aquifers within the Clarence-Moreton Basin sequence are generally low yielding with average yields ranging from 0.5 to 2.5 L/second in the sandstones, siltstones and conglomerates of the Bundamba Group. Reported average and maximum bore yields for the Walloon Coal Measures, Kangaroo Creek Sandstone and Grafton Formation are 0.5, 0.4 and 0.3 L/second, respectively (Brodie, 2007). The maximum yields reported for these aquifers are 5, 10 and 1.5 L/second, respectively. The most significant aquifer in the Clarence-Moreton bioregion Management Area is the Woogaroo Subgroup. The Ripley Road Sandstone is the upper unit in the Woogaroo Subgroup, and is equivalent to the Precipice Sandstone of the Surat Basin. Past investigators have referred to this sequence as the Helidon Sandstone (which is not a current stratigraphic name anymore). The unit comprises fine- to coarse-grained quartzose sandstones occurring from the surface to a maximum depth of 500 m. It is a reliable producer of good quality water, with yields of up to 15 L/second thus providing base flow to the creeks where it is present within the Lockyer Creek.

1.1.4.3.2 Groundwater planning and use

Groundwater planning and management is performed by the respective state governments in the Clarence-Moreton bioregion. Water resources in New South Wales are governed by a number of acts and are administered by the New South Wales Department of Primary Industries, specifically New South Wales Office of Water (Anderson et al., 2013). The Office of Water is primarily responsible for the strategic management of the state’s fresh water resources where groundwater planning and management is implemented through ten-year water sharing plans. Water Sharing Plan Areas are subdivided by Groundwater Management Areas and Groundwater Sources. The major coal producing basins of New South Wales contain 35 Water Sharing Plans, 60 Groundwater Management Areas and 184 Groundwater sources (Anderson et al., 2013). The long-term average annual extraction limits (LTAAEL) for the aquifer systems are reported in respective Water Sharing Plans. The LTAAEL is the proportion of the long-term average annual recharge of water to the groundwater system that is available for extraction. The pre-Cenozoic aquifers are classified into one management unit called the Clarence-Moreton Groundwater Management Area. There is currently limited use of this aquifer system.

Similarly, Water Resource Plans in Queensland have been established for the management of the artesian and some sub-artesian groundwater resources. Great Artesian Basin Water Resource Plan and Resource Operation Plan governs the management of the artesian aquifers. Water sharing plans and water resources plans relevant to the Clarence-Moreton bioregion are listed in Table 8. The allocation and licensing of water are subject to these water sharing/ water resource plans. An entitlement and licence is required to take water from a sub-artesian aquifer mentioned in the Water Resource/Water Sharing Plans.

Various studies conducted in recent years report the overuse of the alluvial groundwater resources in the Clarence-Moreton bioregion. For example, Hair (2007) reported that under the current management and climatic conditions, the Lockyer Valley alluvial aquifer remains under stress with the groundwater resource being heavily pumped beyond the sustainable levels. A water balance calculation by Hair (2007) indicated that during average rainfall years, the total groundwater pumping throughout the Lockyer Valley exceeded recharge by approximately 3375 ML/year. Similarly, enhanced declining trends in the water levels of the Bremer Valley alluvial aquifer have been noted since the 1990s resulting from excessive use. The aquifer risk assessment report published by the New South Wales Department of Land and Water Conservation (1998) classified the Richmond alluvium as a high risk aquifer and the Tweed and Clarence coastal sands as medium risk aquifers. Basalt aquifers of the Alstonville Plateau have been formalised into a groundwater management area which has been classified as a highly stressed aquifer due to the risk of over-extraction or contamination (DLWC, 1998).

1.1.4.3.3 Groundwater monitoring and assessment

Adequate monitoring information is available only for the alluvial aquifers. The Lockyer Valley alluvial aquifer has approximately 400 existing monitoring bores located throughout the valley. Groundwater levels are monitored in most of these bores on a quarterly basis. Around 130 monitoring bores have been recorded in the groundwater database for the Bremer/Warrill alluvium. While the oldest record commenced as early as 1964, there are only a few bores with adequate long-term records. As part of the National Action Plan for Salinity and Water Quality (Pearce et al., 2007a), 50 monitoring bores were installed in the Walloon Coal Measures and Marburg Subgroup aquifers as well as in the alluvial aquifer in the Bremer river basin and the water levels in these bores were measured on a three month basis since 2004. A number of piezometers have been installed in the Richmond River alluvium by the New South Wales Department of Natural Resources in the late 1990s and some have continuous data loggers to record hydrographs of groundwater levels. Similarly long-term monitoring of groundwater levels in the Alstonville basalt aquifers commenced in 1987 with construction of two nested bores and an addition of another seven bores in 1999.

In general, however, groundwater level monitoring is sparse in the bedrock aquifers and this is particularly the case on the New South Wales side of Clarence-Moreton bioregion. For instance, there are not many bores in the New South Wales part of the basin, which have more than 100 records of groundwater level data.

1.1.4.3.4 Knowledge gaps

Based on the literature and database reviews that underpinned this contextual statement, a lack of knowledge on the hydrogeology of the Clarence-Moreton bioregion is significant compared to other basins where CSG activity is taking place such as the Surat Basin. While different aquifer systems have been delineated and characterised, there is a lack of continuous monitoring of water quality and quantity that is adequate enough to support any numerical modelling framework with the exception of the alluvial aquifers of the Lockyer Valley and possibly the Bremer river basin, Warrill Creek and Purga Creek basins. Even for monitored bores, screening information is absent in many instances from the digital groundwater database in New South Wales, which limits the use of these data (although records of the hydrostratigraphic unit of the screened interval may exist as hard copies). Lack of knowledge on the vertical connectivity of the different aquifer layers poses a challenge to any meaningful application of groundwater models to predict the pathways of coal seam gas impacts. It is notable that the water sharing plans for some of the groundwater management areas are in the development phase. Similarly, with groundwater quality monitoring in the New South Wales part of the Clarence-Moreton bioregion, the data are sparse and where available, data quality is often limited. For instance, the depth at which water quality is measured is often missing from the datasets resulting in ambiguity about the aquifer being monitored. In general, scarcity of data that supports hydrogeological characterisation in addition to groundwater quality and quantity data represent the main challenges for the Clarence-Moreton Bioregional Assessment.

Table 8 Water Sharing Plans for the Clarence-Moreton bioregion