Présentations Colloques

Oral Presentation
Session 8.10: Recent developments in groundwater modeling and mathematical tools in Hydrogeology
Cook Scott
Interpreting hydraulic and hydrochemical data in an Australian alluvial aquifer-aquitard system using multivariate statistics
Groundwater in the Mooki River alluvium (New South Wales, Australia) supports a valuable agricultural industry and is important for town water and environmental flows. Irrigation extraction has caused widespread groundwater level decline and local salinity increases are becoming evident. However, despite the high economic and ecological value of the groundwater resource, considerable uncertainty remains in system conceptualisation which translates into uncertainty in appropriate management solutions. **We aimed to reduce this uncertainty and improve understanding of system behaviour by (i) undertaking a statistical assessment of temporal groundwater level and chemistry data to identify chemical and hydraulic trends since the 1960’s+ and (ii) relating these trends to hydraulic connectivity and anthropogenic environmental stresses.**Historic groundwater chemistry records were quality-checked and supplemented with additional targeted sampling. Manual water level readings were historically recorded bimonthly in government monitoring bores. We recorded water levels with dataloggers at 15-minute intervals in representative boreholes for comparison. The hydraulic and hydrochemical time series data were analysed using multivariate statistics and interpreted in the context of lithological setting, groundwater extraction and climatic variability. The 15-minute interval groundwater level data enabled estimation of loading efficiency to distinguish loading response from recharge and an assessment of how monitoring frequency influences interpretation. **Our analysis provided insight into catchment processes and showed how long-term groundwater chemistry trends are related to hydraulic changes in the system. We demonstrated how spatial variations in chemistry and hydraulic response can be related to variations in hydraulic connectivity. We recommend that to adequately characterise the response of this complex aquifer-aquitard system, routine hydraulic and chemistry observations should be supplemented with higher frequency data at targeted sites. Our improved system understanding can contribute to effective groundwater management and enable improved predictions of future stress effects.**