Groundwater modelling report – Southern Riverine Plain. CSIRO: Water for a Healthy Country National Research Flagship

[摘要] A numerical groundwater flow model for the Southern Riverine Plains was initially developed by Sinclair Knight Merz in 2007 (SKM, 2008) as part of the Murray-Darling Basin Sustainable Yields Project. During the course of the current study the model has been updated to reflect more recent groundwater extractions and measured groundwater response, recalibrated and applied in the running of various scenarios based on assumed future climate and future development options.The Southern Riverine Plains is an area which has seen development of the groundwater resource since the early 1970s, with extractions peaking in 2002/03 at slightly over 400 GL. They are currently averaging approximately 305 GL/year. The development in the groundwater resource has seen it become an increasingly important component of water resource management in the basin. The area contains four key environmental assets, the Gunbower-Koondrook-Perricoota Forest, the Barmah-Millewa Forest, the Edward-Wakool River System, including Werai Forest, and the Lower Goulburn Floodplain.A series of seven predictive model scenarios were run for 50 years from 1 July 2010. The results of these scenarios were assessed against four criteria aimed at determining the sustainability of the particular scenario. These criteria are:•Criterion 1. Stabilisation of groundwater levels (key environmental function). To meet this sustainability criterion groundwater levels must have stabilised or be rising at the completion of the scenario model run – i.e. after 43years of extraction at the defined preliminary extraction limit – at the Resource Condition Indicator (RCI) sites. •Criterion 2. Stabilisation of extraction (productive base). The groundwater extraction rates are automatically reduced in groundwater models if a model cell from which groundwater is being extracted dries out due to excessive drawdown. To meet this criteria the model must maintain pumping at the required rate for the duration of the scenario model run. •Criterion 3. Prevention of dewatering confined aquifers (productive base). To meet this criterion the predicted groundwater levels at all RCI sites must remain above the top of a confined aquifer.•Criterion 4. Maintenance of current environmental river flows (key environmental outcome). This criterion mandates that the sustainable extraction limit must be equal to or less than the current level of groundwater extraction. In this regard the current level of groundwater extraction is defined as the average of the last five years of groundwater extraction within the available record – i.e. from 2004 to 2008 inclusive.The scenario modelling predicted that induced river losses to the groundwater system, caused by groundwater pumping, ranged from 280 to 350 GL/year across the entire Southern Riverine Plains model domain. This represented 60 to 75 percent of the total groundwater extraction volumes being realised as ‘losses’ in streamflow. The groundwater modelling undertaken in this investigation suggests that sustainable extraction limits for the modelled area are about 128 GL/year for the Lower Murray region of New South Wales, 302 GL/year for the Victorian Riverine Plain (including 120 GL/a of pumping from the Shepparton Formation in the Shepparton irrigation region) and 27 GL/year for the modelled part of the Ovens-Kiewa Sedimentary Plain. If a precautionary approach is applied in order to account for model uncertainty then the extraction limits should be factored down to 102, 245 and 21 GL/year respectively.

[发布机构] CSIRO

[学科分类] 地球科学(综合)