2.6.1.2.1 Review of surface water models used in the Namoi subregion

This section presents a review of surface water models previously used in the Namoi river basin and discusses the relevance of those to the surface water modelling undertaken for the BA for the Namoi subregion.

Table 3 lists the five surface water modelling studies carried out in the Namoi river basin using four different models. The Namoi subregion, which forms part of the Namoi river basin, is included in all of these studies.

Table 3 Surface water models previously used in the Namoi river basin

Table 4 gives a summary of surface water modelling studies within the Namoi river basin. The right to publish the modelling data (as required in the Bioregional Assessment Programme) from these studies is either unavailable or uncertain in all except those from the Namoi Catchment Water Study and CSIRO’s Murray-Darling Basin Sustainable Yields Project. Except for the Namoi Catchment Water Study, none of the earlier studies assesses the impacts of coal resource development. Consequently, only the LASCAM model used in the Namoi Catchment Water Study is further reviewed in this section.

Table 4 Summary of Namoi surface water modelling studies and suitability of their use in the bioregional assessment

^aRiver routing was done.

^bDetailed climate trends not described in Schlumberger (2012).

^cRiver modelling using inflow to the reach (no consumptive use and regulation modelled).

na = not available

*right to publish modelled data

Namoi Catchment Water Study

Schlumberger Water Services (SWS) used the LASCAM hydrological model (Viney et al., 2000; Sivapalan et al., 2002) for surface water modelling in the Namoi Catchment Water Study. The modelling domain covers eastern and central surface water catchments above a location approximately 6 km upstream of Narrabri comprising the Peel River catchment and areas upstream of Keepit Dam (Schlumberger, 2012). Thus, SWS’s domain covers all coal mine development sites and most of the area of coal seam gas (CSG) future development sites identified in the CRDP for the Namoi subregion.

Data and model calibration

LASCAM was used on a series of 99 linked subcatchments, which were characterised in terms of land use and vegetation characteristics, and stream channel geometry. The input data used were rainfall, evaporation, vegetation cover, land use and soil type. A daily time step was used in calibrating the model using input data from 1996 to 2010. Among other observed variables the daily streamflow and flow duration curves were used to compare the modelled and observed results in calibration. A reference climate was derived from repeating 20 years of data from 1990 to 2009 and simulations were run for 90 years from 2010 to 2100 using the reference climate. No mention of river system modelling or river routing is found in Schlumberger, (2012), though routing is an integral component of LASCAM.

Scenarios used

Eight different development scenarios were modelled in the Namoi Catchment Water Study (Table 5). Of these, the scenario most comparable to the baseline future for the BA for the Namoi subregion is scenario 1, which considers six approved open-cut coal mines and one underground coal mine (Table 5). The difference between scenario 1 and the BA baseline is that the former includes the Canyon Coal Mine, which, since it closed in 2009, is not included in the latter.

The scenario in the Namoi Catchment Water Study that most closely approximates the CRDP future in BAs is scenario 2 which augments scenario 1 with two new open-cut coal mines, two expanded open-cut coal mines, one underground coal mine and two CSG developments. Scenario 2 includes one CSG field (Santos’ Bando CSG field) as well as the Canyon Mine which are not in the CRDP. Conversely, scenario 2 does not include the Vickery Coal Project or the Narrabri South underground coal mine, both of which are in the CRDP.

The Namoi Catchment Water Study reports that the main impacts to surface water will be derived from open-cut mining with little impact predicted from CSG or underground mine development. Predicted differences in long-term (2010–2100) average streamflow between scenario 1 and scenario 2 are reductions of approximately 0.1% at three locations in the Namoi River (approximately at Gunnedah, Boggabri and Narrabri) and approximately 0.0% and 0.2% at two locations in the Mooki River (Breeza and Ruvigne).

Table 5 Development scenarios used in Schlumberger’s modelling study

CSG = coal seam gas

Data: Schlumberger (2012)