VGP Technical Report 36 - Gippsland Groundwater Model (GGMv1.1) Groundwater impact assessment -Re-calibration of numerical model
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Product description:About the Victorian Gas Program: The Victorian Gas Program (VGP) is a comprehensive science-led program, incorporating geoscientific and environmental research to assess the risks, benefits and impacts of potential onshore conventional gas exploration and production. The program is also investigating the potential for further discoveries of onshore conventional and offshore gas in the Otway and Gippsland geological basins and assessing the feasibility of additional onshore underground gas storage in depleted reservoirs around the Port Campbell area. The VGP includes an extensive, proactive and phased community and stakeholder engagement program, through which the results of the scientific studies are being communicated. Executive summary: A regional-scale groundwater impact assessment model has been re-calibrated and deemed as fit for purpose as part of the Victorian Gas Program (VGP). The numerical model is a revised version of a previous groundwater model of the Gippsland Basin, from the 2015 Victorian Water Science Studies (VWSS). The model has been used to assess the potential impacts onshore conventional gas development may have on groundwater in the Gippsland Basin. As part of the VGP environmental studies, the Geological Survey of Victoria (GSV) recalibrated a Gippsland groundwater model from the VWSS program in order to quantify potential groundwater impacts from onshore conventional gas development in the Gippsland Basin. The model is required to quantify individual and cumulative impacts from hypothetical development scenarios, including changes to groundwater levels and pressures, changes to river baseflows, and changes to water availability for groundwater dependent ecosystems. This Gippsland groundwater model was revised in two stages: 1. Re-calibration of a numerical groundwater model to simulate conventional gas development using the previously constructed conceptual groundwater model. 2. Application of hypothetical gas development scenarios to assess potential impacts to existing groundwater conditions in the Gippsland Basin. This report presents the first stage, summarising the model’s development and recalibration to simulate potential impacts of onshore conventional gas development in the Gippsland Basin. The model was calibrated using automated and manual methods to ensure aquifer parameters and calibration targets remained within acceptable ranges. All available groundwater monitoring data was compiled and included for both the steady-state and transient model calibrations. Primary calibration targets were the depth to watertable and the modelled versus measured groundwater levels. Calibration of the steady-state model showed that modelled flow paths were generally in good agreement with flow paths expected from the theoretical considerations developed in the conceptual model. The transient model calibration was based on calibration in which parameter optimisation was applied for the period 1990–2018. The aquifer parameterisation of layers attributed within the Strzelecki Formation was revised following a previous review of the Strzelecki Formation parameterisation. Transient conditions for the period 1960–2018 revealed satisfactory correlation between modelled and measured data during the initial 30 years of simulation. This period was a transition from pseudo-steady conditions to temporal conditions when stress periods were at annual intervals. This suggests that the simulated steady-state solution describes the 1980 groundwater conditions adequately. During the 1980–1999 calibration period there was a scaled RMS of 3.99 per cent, which improved during the 2000–2018 calibration period to a scaled RMS of 2.68 per cent. Assumptions have been made in the calibration as a result of limitations that determine the spatial and temporal variation uncertainties in the model. These assumptions provide a foundation for the development of the model. Whilst there is always some level of uncertainty, the best available data has been used to limit associated errors. Review of the spatial and temporal model calibration data, and the results of sensitivity analysis, has confirmed that the numerical groundwater model is appropriate for assessing predicted groundwater level changes under the hypothetical onshore conventional gas development scenarios proposed. Bibliographic reference: HOCKING, M., BEVERLY, C., BOLD, T.A. & IVERACH, C. 2020. Gippsland Groundwater Model (GGM v1.1) Groundwater impact assessment - Re calibration of numerical model, Onshore Gippsland Basin, Victoria. Victorian Gas Program Technical Report 36. Geological Survey of Victoria. Department of Jobs, Precincts and Regions. Melbourne, Victoria. 271p. Download: The downloadable version of this report is supplied in PDF format (PDF 130 MB). | ||||||
