Surface Water-Groundwater Model Development for Integrated Assessment
Creators: name: Blakers, Rachel
Publisher: name: The Australian National University
Year: 2022

description: This thesis develops an approach to the modelling of connected surface water and groundwater resources that is designed to support the needs of those who undertake integrated modelling and assessment. The research is motivated by an integrated assessment (IA) project undertaken in the Namoi Catchment in New South Wales, Australia, which examines the social, economic, and ecological consequences of water resources management decisions. To better understand the catchment-scale hydrogeological processes operating in the study area, two data-mining techniques are developed that exploit readily available hydrometric data. The first is a cluster analysis of groundwater hydrographs to improve knowledge of the connectivity between aquifers; the second looks at correlations between cumulative rainfall departure (CRD) and groundwater levels to gain insight into recharge pathways and the impacts of groundwater extractions. The results of the analysis have implications for conjunctive water management, highlighting areas of connectivity where groundwater extraction is likely to be supported by surface water recharge, and areas of disconnection where extraction risks mining the alluvial aquifer. The work also informs the design of a suitable integrated surface water-groundwater (SW-GW) modelling approach. For SW-GW modelling to support IA, a key challenge is to minimise data requirements and computational complexity while maintaining a sufficiently good representation of system behaviour to support the needs of socio-economic and ecological analyses. A survey of existing surface water and groundwater models examines the strengths and weaknesses of various methodologies. Based on the findings of the survey, two novel SW-GW models are devised to meet the specific needs of IA projects and address gaps in existing tools. The first model, IRG-lumped, is a spatially-lumped, conceptual model that represents hydrogeological processes at the catchment scale. The second model, IRG-spatial, replaces the groundwater component of the IRG-lumped model with a spatially-distributed, physics-based approach. The IRG-lumped and IRG-spatial models are calibrated and validated for Maules Creek Catchment, a sub-catchment of the Namoi. Uncertainties in the model parameters and outputs are examined using an ensemble of independent calibrations. Even though both models are designed to be relatively parsimonious, they still suffer from a high degree of parameter uncertainty. This is partly due to the complex hydrogeology of the Maules Creek Study Area and limitations in the available observational data. For use in IA projects, the two models have varying strengths and weaknesses. For projects where the primary aim is to simulate groundwater-dominated baseflows, the IRG-lumped model may be preferred as it runs quickly and does not need detailed information on aquifer hydrogeology. The Maules Creek application demonstrated that the model is able to simulate average changes in groundwater heads in a sloping aquifer. However, choosing an appropriate, spatially-lumped representation of a heterogeneous aquifer can be challenging, requiring extensive data analysis and the application of expert judgement. The IRG-spatial adds value if the calculation of spatially varying groundwater heads is needed, but it is more computationally intensive. Unexpectedly, it can be easier to apply than the IRG-lumped model if suitable data is available, since it deals naturally with aquifer heterogeneity. The results of this research demonstrate that, for IA projects, neither approach is unequivocally superior for modelling connected surface water and groundwater systems. The appropriate model must be chosen considering the needs of the specific project and the physical characteristics of the study area.