Groundwater modelling report - Lower Gwyder.CSIRO: Water for a Healthy Country National Research Flagship

[摘要] An existing numerical groundwater flow model (Bilge, 2002) was applied to assess impacts of various assumed future climate and development scenarios. The original model was not updated or revised, but it was translated from an older version of the modelling software. The calibration was checked and found to be consistent with the original. The groundwater model was used to assess the long-term impact of a preliminary extraction limit for groundwater pumping from the Lower Gwydir alluvial aquifers. Predictive models were developed and run for six fifty-year scenarios and the results assessed against four criteria aimed at determining the sustainability of the particular scenario. Thesecriteria are: Criterion 1. Stabilisation of groundwater levels (productive base and key environmental outcome requirement). To meet this sustainability criterion groundwater levels must have stabilised or be rising at the completion of the scenario model run (i.e. after 43 years of extraction at the defined preliminary extraction limit) at the RCI (Resource Condition Indicator) sites. Criterion 2. Ability to maintain volume of extraction (productive base requirement). 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 of confined aquifers (productive base and key environmental outcome requirement). To meet this criterion the predicted groundwater levels at all RCI sites must remain above the top of a confined aquifer. Criterion 4. Impact on surface-water streamflows (key environmental assets and key ecosystem functions requirement). 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. Current levels of groundwater extraction are about 41.3 GL/year and the NSW Water Sharing Plan target has been set at a level of 32.3 GL/year. Model results indicate that annual extraction of 32.3 GL/year appears to be sustainable, provided local management rules are implemented, when assessed against the four sustainability criteria used in this study. Onthis basis a preliminary extraction limit of 32 GL/year is proposed, factored down to 24 GL/year to account for model uncertainty.

[发布机构] CSIRO

[学科分类] 地球科学(综合)