The limitations on the surface water balance estimates provided here are a result of the limitations in the numerical modelling. The surface water numerical modelling is described in companion product 2.6.1 for the Belyando river basin (Karim et al., 2018) and should be read in conjunction with discussion on surface water balance in this product.
The limitations on the conceptual groundwater balance estimates provided in this section are a result of gaps in the understanding of groundwater processes such as the volumes and rate of inter-aquifer flow, evapotranspiration rate, fluxes between surface water and groundwater and the level of detail available in mine EISs on groundwater inflows and external water requirements. The Bioregional Assessment Programme (Dataset 1) includes information on data source and reliability. Other limitations include only using one method to estimate recharge from rainfall and not taking into account the effects of vegetation cover on recharge rates.
The degree and distribution of connectivity between shallow groundwater systems and surface drainage is not well understood in the area covered by the surface water and conceptual groundwater balance (Belyando river basin). This has a bearing on whether there may be an overestimation or underestimation of any surface water – groundwater fluxes, which in turn would have an effect on uncertainty in the water balances, and surface water and groundwater modelling. There is potential that small changes to the groundwater discharge component of the water balance may cause changes to components of the surface water balance, such as low-flow indices and increase in number of zero-flow days. It is difficult to represent such variability in a water balance. Furthermore, as detailed in Bainbridge et al. (2014) and Section 3.3 of companion product 3-4 for the Galilee subregion (Lewis et al., 2018), natural streamflow for the Belyando River and the Burdekin river basin on a whole varies considerably from year to year, which can include long periods of no stream flow. This has a direct bearing on the surface water budget for any given year and to the degree that surface water – groundwater interactions may occur.
The utilisation of more sophisticated analysis methods and other datasets (e.g. remote sensing) to estimate evapotranspiration and recharge may decrease uncertainty for this component of the water balance. As an example, Section 3.5 of companion product 3-4 for the Galilee subregion (Lewis et al., 2018) includes a qualitative interpretation derived from the Landsat archive of Digital Earth Australia (Geoscience Australia, 2017) of aspects of the local hydrology for springs at the Doongmabulla Springs complex. As outlined in Section 3.7 of Lewis et al. (2018), further work utilising the Landsat archive could be undertaken to quantify some of the hydrological processes that are evident in the imagery.
The assumption behind the calculation of the conceptual groundwater balance is that the groundwater flow systems are in equilibrium (Section 22.214.171.124.2). This assumption can be further tested by improving the understanding of groundwater flow pathways and the use of environmental isotopic tracers.
As discussed in detail in Section 2.1.5 of companion product 2.1 for the Galilee subregion (Evans et al., 2018b) the assumption that all baseflow in the Burdekin river basin is derived from fully saturated groundwater discharge and not through other processes, such as interflow, should be tested.
Water allocations from water supplies that are external to mine development areas are yet to be finalised. The amount of external water required will vary from year to year and would depend on factors including: stage of life for the mine development, actual groundwater inflows to mine areas, available rainfall harvested on-site, and amount of water available from surface water systems.
Further discussion on gaps and opportunities for future work are also outlined in Section 3.7 of companion product 3-4 for the Galilee subregion (Lewis et al., 2018). Future iterations could also investigate the water balance post-closure of the mines, and include other factors such as water stored in remanent open-cuts, changes to groundwater recharge and groundwater flow fluxes out of the model area, and changes to recharge rates due to climatic variation.
Product Finalisation date
- 2.5.1 Methods
- 2.5.2 Water balances
- Currency of scientific results
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- About this technical product