4.1 Surface water

Activities that block or obstruct small flood runners are of ‘potential concern’ in about 6% (1,613 km2 ) of the Cooper Creek floodplain, excluding the riparian and wetland areas. Ongoing site-based assessment and investigation of changes to agricultural productivity, protected wetlands, and protected fauna and flora on the floodplain is warranted to protect these sensitive ecosystems. Water-affecting activities are regulated under state legislation to mitigate potential impacts on sensitive areas

Changes in runoff and annual flows are often difficult to detect given the large variability in runoff response and inaccuracy of stream gauge data, especially for low flows (Tomkins, 2014; Zhang et al., 2018). Overland flow obstruction decreases the extent and duration of floodplain inundation (Figure 59, Butcher and Hale, 2011). Tall embankments and soil removal to form the embankments, which are no longer standard practice, have altered inundation patterns at Embarka Swamp (Reid, 1988). Embarka Swamp is located on the Main Branch of Cooper Creek in the Coongie Lakes Ramsar wetland site. These and other impacts can be avoided by careful design to minimise flow obstructions and impoundments (refer to the civil construction node description). Estimates of water impounded under a maximum likely future resource development scenario are unlikely to be greater than a conservative estimate of the minimum detectable change in annual flows at a stream gauge (refer to the overland flow obstruction node description).

Activities that impact on water are regulated to limit the extent of an affected watercourse or volume of water that is impounded (Department of Environment and Science (Qld), 2016; South Australian Arid Lands Natural Resources Management Board, 2017a). Proponents have strategies to avoid or mitigate overland flow obstruction during civil construction (for example, Santos (2015); Senex Energy (2016); Beach Energy (2019)). There is high confidence that state and regional regulations, as well as industry mitigation strategies, can mitigate potential impacts in sensitive areas.

Flooding can be catastrophic for agricultural production in terms of loss of stock, fodder, topsoil and crops, as well as damage to surface infrastructure. However, flooding is also essential for riparian and wetland ecosystems, with flood pulses replenishing instream waterholes, and connecting wetlands with main river channels. Detailed flood modelling enables careful design of roads and other infrastructure on the floodplain to minimise flow obstructions, impoundments and damage to infrastructure. The user panel for the Cooper GBA region identified a need for detailed flood modelling to better understand how resource development could impact the floodplain and landscape of the Cooper GBA region ( Box 2 ).

Box 2 Collecting data to build a hydrodynamic flood inundation model of Cooper Creek floodplain

The Cooper Creek floodplain spans across Queensland and South Australia, is large (about 32,000 km 2) and floods frequently. It has extremely complex terrain, very low gradients and sparse observed data. It is among one of the most complex floodplains in the world and is by far the most complex floodplain in Australia. Until now, detailed floodplain inundation modelling has never been attempted in the region due to the size and complexity of the Cooper Creek floodplain.

In 2019, the Program conducted light detection and ranging (LiDAR) aerial surveys covering an area of 31,780 km 2 across the Cooper Creek floodplain, and the Thompson and Barcoo river systems.The digital elevation model developed from the LiDAR dataset has been used to build a hydrodynamic flood inundation model to better understand how and where to manage potential impacts on the floodplains of the Cooper GBA region.

The LiDAR data are available for download in 1 km 2 tiles through the national Elevation Information System (ELVIS) data portal or from data.gov.au . The digital elevation model can be used by regulators, proponents and the public to inform decisions and improve future management and protection of Cooper Creek floodplain.

The calibrated hydrodynamic flood inundation models developed for the Cooper GBA region can evaluate how flood characteristics may change under future development and climate change scenarios in the complex Cooper Creek floodplain ( Box 3 ). The size and complexity of Cooper Creek floodplain meant the flood model was divided into the Queensland (23,000 km 2 with 7,420,953 mesh elements) and South Australia (9,000 km 2 with 4,754,440 mesh elements) models.

Box 3 State-of-the-art 2D hydrodynamic flood inundation models

For the first time, a state-of-the-art 2D hydrodynamic flood inundation model (MIKE21FM) has been developed for all 32,000 km 2 of the Cooper Creek floodplain. The flood inundation model was calibrated using stream gauge and satellite monitoring data for historical floods. There is good agreement between the calibrated model and Landsat and MODIS satellite data for historical floods in an area characterised by extremely complex terrain, very low gradients and sparse water level observations. Figure 11 shows the modelled extent of 1-in-10-year floods for the Queensland and South Australia flood models. Different dates are shown for each model as the spatial extent of data meant that satellite data to calibrate the model was not available for both areas at the same time.

FIGURE 11 Modelled extent of a 1-in-10-year flood showing modelled flood depth on 31/01/2004 for the Queensland flood model (model area 1) and on 03/04/2010 for the South Australian flood model (model area 2 )

Model 1 is from the Stonehenge and Retreat stream gauges north of Windorah, Queensland to the Nappamerri stream gauge east of Innamincka. Model 2 is from the Nappamerri stream gauge past Innamincka, north of Moomba to Coongie Lakes wetland area in South Australia. Flood depth is typically less than 3 m and is greater than 5 m in waterholes, Lake Yamma Yamma and Coongie Lakes wetland.

The Queensland flood model extends from the Stonehenge and Retreat stream gauges in Queensland to the Nappa Merrie stream gauge in South Australia. The South Australian flood model extends downstream from the Nappa Merrie stream gauge into Coongie Lakes wetland area.

Data: Geological and Bioregional Assessment Program (2021e)

Element: GBA-COO-3-694

Any accidental release of contaminants into surface waters could spread rapidly and accumulate in sediments and so is of ‘potential concern’ in 12% of the Cooper GBA region. Compliance reporting in Queensland and South Australia demonstrates that existing state-based regulations, approval conditions and industry practices designed to avoid spills and leaks, and in the event of a spill to ensure remediation occurs quickly, are effective.

Chemicals or compounds used or produced in unconventional gas resource development can be unintentionally released to the environment beyond any engineered bunding or control, including spills and leaks of liquid or solid contaminants. Surface water contamination leading to pollution due to accidental release, or from accidental release via soil contamination, occurs when the concentration of a biological, chemical or physical property is sufficient to cause an adverse effect (refer to the soil contamination and surface water contamination node descriptions).

Potential impacts due to accidental release are primarily managed through existing avoidance and mitigation strategies prescribed in state-based regulations (Government of South Australia, 2015; Department of Environment and Science (Qld), 2016) (refer to the accidental release node description). The assessment assumes that if an accidental spill occurs there are limited options to avoid or remediate surface water contamination due to more rapid spreading of chemicals through surface water and partitioning to and accumulation in sediments (National Research Council, 2000; Eggleton and Thomas, 2004; Jaffé, 1991). This highlights the importance of compliance with existing state-based regulations and approval conditions to avoid spills and leaks. Confidence in existing avoidance and mitigation strategies is high. However, there is insufficient species-specific information to establish robust thresholds to evaluate material thresholds for the toxicity of potential pollutants for protected fauna.

Controlled release of wastewater to the environment is of ‘low concern’ as it is strongly regulated by both the Australian Government and state governments. Stringent approval conditions, monitoring, treatment and compliance requirements ensure that the treated wastewater is consistent with the sensitivity of the receiving environment.

Controlled release of wastewater is the intentional and approved release of treated water into the environment, including evaporation from storage ponds, reuse for operations water, dust suppression, irrigation or stock drinking water, and disposal of treated wastewater into existing drainage features in the landscape or by reinjection into deep underground formations such as depleted oil and gas reservoirs or deep unused aquifers (Holland et al., 2020).

Quality of treated wastewater released to surface waters is closely monitored and strongly regulated by both the Australian Government and state governments (Commonwealth of Australia, 2014). While there is very little baseline water quality information available for the Lake Eyre Basin, the water quality requirements stipulated in approval conditions are informed by the Australian and New Zealand Guidelines for Fresh and Marine Water Quality (ANZG, 2018) and are designed to prevent adverse effects of contamination of soils, surface waters, aquifers and riparian or floodplain environments. There is high confidence in the cause-and-effect relationships and existing mitigation strategies, and low confidence in the material change thresholds for protected fauna, flora, wetlands and areas.

Water-affecting activities are regulated under state legislation to mitigate potential impacts on sensitive areas. There is high confidence that licensed surface water extraction – currently approximately 2% of annual flows – is of ‘low concern’ as it will not materially alter channel flows, scouring or flooding in Cooper Creek.

Surface water can be extracted from water flowing in channels and the water stored in waterholes. Surface water extraction could reduce channel flows downstream of the extraction point. A licence is required in both Queensland and South Australia (refer to the civil construction drilling and hydraulic fracturing node descriptions) under the relevant water sharing plans.

Total licensed surface water extraction for all water users is approximately 30 gigalitres per year, or about 2% of annual surface water flows in Cooper Creek at Nappa Merrie (gauge 003103A) (Santos, 2017; Geological and Bioregional Assessment Program, 2018a). Total estimated water volumes (surface water, groundwater and reuse of co-produced water) needed over 50 years for the maximum resource development scenario is approximately 400 megalitres per year. This contrasts with extraction of 40,000 megalitres per year from Cooper Creek as part of unsuccessful irrigation proposals in the 1990s and 2000s (for example, Walker et al. (1997); Carini et al. (2006); Sheldon et al. (2010)) (refer to the channel flow node description).

There is high confidence that surface water extraction for future development will not materially alter channel flows, scouring or flooding in Cooper Creek. This is supported by state and regional water allocation regulations, total extraction volumes and mean annual flows in Cooper Creek. However, less is known about how material changes to floodplain inundation and scouring will affect environmental values.

Last updated: