Groundwater systems System boundaries and hydrostratigraphic units

The major hydrostratigraphic units present in the Clarence-Moreton bioregion are:

  • Cenozoic to recent alluvium and volcanic formations
    • alluvial systems are shallow formations along the river valleys and flood plains within the basin and the volcanic formations include the Cenozoic basalt aquifers. The alluvial aquifer systems include the Lockyer Valley alluvium, the Bremer River, Warrill Creek and Purga Creek alluvial systems, the Logan/Albert river alluvial systems, the Tweed River alluvium, the Clarence River alluvium and the Richmond River alluvium.
  • Jurassic to Cretaceous sandstones
    • including the Grafton Formation, the Orara Formation, the Walloon Coal Measures, the Koukandowie Formation and the Gatton Sandstone
  • Woogaroo Subgroup
    • with a Triassic to Early Jurassic origin
  • basement aquifers
    • Paleozoic age basement rocks, Permian to Triassic intrusive rocks and Permian to Triassic sedimentary and metasedimentary rocks.

Alluvial aquifer systems

Alluvial aquifers are the major source of groundwater supply within the basin. The unconfined alluvial aquifers receive much of their recharge from river and creek beds as well as from rainfall (diffuse) recharge. In the headwaters and especially where the alluvial aquifers are incised deep into the Main Range Volcanics, bedrock also is a substantial contributor of recharge to the alluvium. In addition, at the edge of the alluvial aquifer systems, Clarence-Moreton bioregion formations recharge the alluvium locally.

The Lockyer Valley alluvium extends over more than 200 km2 and is approximately 30 to 35 m thick (Hair, 2007; Cox and Raiber, 2013) throughout much of the unconfined to semi-confined aquifer. It is one of the most heavily developed aquifer systems in the Clarence-Moreton bioregion. The alluvium is characterised by coarse gravel towards the headwater areas in the southern tributaries where the gradient is steep; the gradient decreases towards the north-east where the alluvium is dominated by clay, sandy clay, sand, sandy gravel or gravel. The alluvial sediments are generally marked by fining-upwards sequences throughout the Lockyer Valley. The central and lower portions of the valley have a considerable cover of clays ranging from a thickness of 2 to 20 m. The groundwater yields from the alluvium ranges up to 50 L/second, although low supplies in the order of 0.01 L/second have also been reported (Pearce et al., 2007b).

The Bremer River, Warrill Creek and Purga Creek alluvial systems are composed of Cenozoic to Quaternary alluvial and colluvial sediments, deposited along the major drainage systems spread over the Bremer river basin which is located 40 km south-west of Brisbane and which is a tributary system to the Brisbane River. The aquifer material generally consists of unconsolidated alluvial and colluvial sediments adjacent to existing channels and drainage lines with the flood plain sediments being predominant in the lowermost sections (Pearce et al., 2007a).

Most of the groundwater resources in the Logan sub-basin are found in the Logan/Albert rivers alluvium, and this also includes smaller tributaries such as Teviot Brook. The majority of the alluvium where most of the groundwater is extracted has a thickness ranging between 5 and 25 m in this sub-basin. Further details of the alluvial aquifer in the Logan sub-basin are reported in the Logan Basin Draft Resource Plan - Environmental Investigations Report – Volume I (DNRM, 2007).

The Tweed River alluvium is composed of the shallow ‘upriver’ alluvial aquifer and the coastal floodplain alluvial aquifers. The shallow ‘upriver’ alluvial aquifer is characterised by coarse material and is well connected to the surface water system. The coastal floodplain alluvial aquifers are composed of relatively fine material often interspersed with silt and clay layers. The Richmond River alluvium belongs to the north-east of the New South Wales part of the Clarence-Moreton bioregion. It comprises Quaternary fluvial and estuarine sediments of gravel, sands, silts and mud. They form unconfined to semi-unconfined aquifers with medium to high permeability. These aquifers are generally shallow with good water quality and yields in the order of 0.5 to 1 L/second (Brodie, 2007). Similarly, the Clarence and Coffs river alluvial systems are formed by the Clarence River and cover an area of about 924 km2 in the New South Wales part of the Clarence-Moreton bioregion.

Bedrock aquifer systems

The Main Range Volcanics have thicknesses of typically less than 250 m near Toowoomba (Figure 18, Section 1.1.3) but reach maximum thicknesses of up to 900 m in the southern Main Range (Section They are one of the most important aquifer systems in the Clarence-Moreton bioregion. While there is only limited irrigation associated with the basalts of the Main Range due to the steep gradients, they have a strong influence on recharge to alluvial aquifer systems and are a major source of creek flow particularly in the headwaters of the Lockyer Valley basin, Bremer/Warrill river basins and in the Logan river basin.

The Alstonville Plateau basalt aquifers represent an area of highland basalts that rise up above the alluvial floodplain sediments, located between Lismore and Ballina, and covering an area of approximately 391 km2. The Cenozoic basalt sequence is recognised as an important aquifer system in the Lower Richmond river basin in the Clarence-Moreton bioregion in north-east New South Wales. The aquifer is comprised of a Cenozoic Basalt Plateau that overlies older sedimentary rocks of the Clarence-Moreton bioregion. They also include the Lismore Basalt unit, which is the south-easterly portion of the larger Lamington Volcanic. The aquifer nature range from shallow unconfined to deep semi-confined aquifer systems in fractured horizons.

In the New South Wales part of the Clarence-Moreton bioregion, the alluvial deposits are underlain by the Orara and Grafton formations, Walloon Coal Measures and the Marburg Subgroup (consisting of Koukandowie Formation and Gatton Sandstone, Section 1.1.3). While unconfined groundwater systems occur at shallow depths in the alluvial systems, Cenozoic volcanics and older sediments of the basin, the sandy nature of Kangaroo Creek Sandstone and Piora members suggests that they may act as confined aquifers or aquitards at depth in the basin. But they have poor aquifer properties below about 150 m and have limited hydraulic communication beyond a limited area adjacent to the outcrop (Doig and Stanmore, 2012). The Rappville and Bungawalbin members in the Grafton and Orara formations are likely to act as aquicludes and thus prevent vertical migration of water across them thus isolating any local aquifer system that may exist (Doig and Stanmore, 2012). Much more work is required to verify the hydraulic nature of these formations.

The Walloon Coal Measures are often considered as an aquitard on a regional scale due to their low permeability and storage capacity. They are dominated by fine-grained sediments and contain shales and siltstones. However, particularly towards the basin margin, sandstones are more dominant in the Walloon Coal Measures sequence, and the Walloon Coal Measures are likely to act as an aquifer in these areas (Doig and Stanmore, 2012). The Mclean Sandstone, which represents the upper part of the Walloon Coal Measures, as well as the underlying Koukandowie Formation are considered as low permeability aquifers, aquitards or aquicludes at depths below any near surface groundwater system influence (Doig and Stanmore, 2012). The Gatton Sandstone underlying the Koukandowie Formation is also a low permeability aquifer. The Woogaroo Subgroup contains quartzose sandstone, shale, siltstone and conglomerate and has medium-grained sandstones devoid of carbonaceous material and is considered to be a good aquifer system.

In the Queensland part of the Clarence-Moreton bioregion, the Grafton and Orara formations are absent and the Quaternary alluvium and Cenozoic Main Range Volcanic rest directly above the Walloon Coal Measures. Other older formations follow similar hydraulic characteristics as in the New South Wales side of the basin. It may be noted that the hydraulic characteristics of these formations are generalised and are likely to be variable in different parts of the basin due to the variable nature of lithology within each lithographic unit (Section 1.1.3).

Basement aquifer systems

Only very limited data are available on the hydrogeology of the hydraulic basement to the Clarence-Moreton bioregion and the basement blocks that limit the Clarence-Moreton bioregion in Queensland and New South Wales. While there is only limited information available, yields are likely to be low, although higher yields of up to 16 L/second have, for example, been reported for the Neranleigh Fernvale Beds near the Gold Coast (Metgasco, 2007). Variable yields have also been reported for Permian to Triassic intrusive rocks in south-east Queensland (Helm et al., 2009), with typical yields ranging up to 2 L/second, but higher yields of 2 to 5 L/second obtained in areas of locally enhanced fracturing. However, generally, most of the basement rocks are assumed to have relatively limited storage (Helm et al., 2009).

Last updated:
8 January 2018
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