Surface water numerical modelling for the Galilee subregion. Product 2.6.1 for the Galilee subregion from the Lake Eyre Basin Bioregional Assessment.

Karim, Fazlul and Viney, Neil and Wang, B and Peeters, Luk and Zhang, Y. and Marvanek, SP and Shi, Xiaogang and Yang, Ang and Buettikofer, H (2016) Surface water numerical modelling for the Galilee subregion. Product 2.6.1 for the Galilee subregion from the Lake Eyre Basin Bioregional Assessment. CSIRO PUBLISHING. ISBN 9781925315370

Abstract

Coal and coal seam gas (CSG) development can potentially affect water-dependent assets (either negatively or positively) through a direct impact on surface water hydrology. This product provides modelled estimates of potential surface water changes due to likely coal resource development in the Galilee subregion. First, the methods are summarised, followed by details regarding the development of the model. The product concludes with predictions of the hydrological response variables, the hydrological characteristics of the system that may change due to coal resource development. The uncertainty and limitations of the models are also reported. The difference in results between baseline and the CRDP is the change that is primarily reported in a BA. This change is due to the additional coal resource development (ACRD) – all coal mines and CSG fields, including expansions of baseline operations that are expected to begin commercial production after December 2012. There are no coal or CSG developments in operation as of the last quarter of 2012 for the Galilee subregion for the baseline coal resource development. There are 17 proposed new developments in the Galilee subregion for ACRD. There is enough available information to include seven of these developments in the numerical modelling for the Galilee subregion.The seven development projects being modelled are the open-cut coal mines Alpha Coal Project and Hyde Park Coal Project, and the combined open-cut and underground coal mines Carmichael Coal Mine, China First Coal Project, China Stone Coal Project, Kevin’s Corner Mine and South Galilee Coal Project. A generic methodology for surface water numerical modelling in the Bioregional Assessment Programme is presented in companion submethodology M06 (as listed in Table 1). This product describes how the methodology has been applied in the Galilee subregion. Numerical simulation of the likely changes in surface water due to coal resource development requires a model or model sequence that can simulate change in the regional groundwater system, the alluvial groundwater system and the stream network. In the Assessment for the Galilee subregion an indirectly coupled model sequence of two models – consisting of a regional groundwater analytical element model (referred to as GW AEM) and a rainfall-runoff model (the Australia Water Resource Assessment Landscape model, referred to as AWRA-L) – is used to simulate the hydrological changes on the surface water systems of the subregion. Development of a single coupled and integrated surface and groundwater model is beyond the resources and data available for the Galilee subregion bioregional assessment. The surface water modelling domain comprises the Belyando, Cape and Suttor river basins and includes 61 model nodes at which daily streamflow is predicted. The model simulation period is from 2013 to 2102. The prediction results show that the ACRD in the Galilee subregion can have substantial impact on the hydrological response variables. The comparison among the 61 receptors shows that for the hydrological response variables that characterise high flow conditions, the relative hydrological changes are larger for the receptors where the maximum ACRD percentage is larger. In general, the biggest impacts (flow reductions of up to 20%) occur immediately downstream of ACRD developments and are particularly evident in receptors where the footprint forms a large proportion of the receptor catchment. For every high flow hydrological response variable, the biggest impacts are predicted to occur at a modelling node with a small upstream catchment on Sandy Creek. This node is located downstream of the South Galilee Coal Project. The ACRD impacts on the low streamflow hydrological response variables appear to be more substantial than those on the high streamflow hydrological response variables. However, they also appear to be associated with greater uncertainty in both the predicted change and the timing of the maximum change. For the low flow variables the biggest impacts occur in the middle reaches of the Belyando River and reflect an accumulation of impacts from multiple developments. These results also suggest that changes to low flow characteristics are caused by a combination of the instantaneous impact of interception from the additional mine footprints and the cumulative impact on baseflow over time caused by groundwater table drawdown, while the changes to high flow characteristics are dominated by direct interception of runoff. The change in baseflow due to changes in surface water – groundwater interactions under the CRDP is small compared to other components of the water balance and the effect of rainfall interception by mine sites. In the Galilee subregion, the accuracy with which mine footprints are represented depends fully on the resolution of the planned mine footprints provided by the mine proponents. This therefore is one of the crucial aspects of the surface water model as it potentially has a high impact on predictions and it is driven by data availability rather than availability of resources or technical issues. Outputs from the surface water modelling are used for the receptor impact modelling (see companion product 2.7 for the Galilee subregion) and in the impact and risk analysis (see companion product 3-4 for the Galilee subregion).