Parameter efficient prediction of unconfined groundwater levels and streamflow

The aims of this research were to critically examine different approaches to predicting unconfined groundwater elevations and streamflow; to develop and test a parameter efficient model for the prediction of groundwater elevations and streamflow given spatially varying climatic variables; and to use the model to investigate possible effects of climate change on groundwater levels and streamflow in the Australian Capital Territory (ACT). A range of available techniques, processbased, empirical and conceptual, for groundwater level predictions together with water balance models were critically examined. Conceptual and empirical models were selected for examination. The data used in this research included: monthly groundwater level records from five to thirty years in length for thirty two bores in consolidated alluvial soils in the ACT and one bore in New South Wales (NSW); and monthly rainfall and pan evaporation data for south eastern Australia. Elevation dependent tri-variate thin-plate smoothing splines were used to spatially interpolate the monthly rainfall and pan evaporation data to allow modelling of groundwater levels in bores where there were no nearby rainfall or pan evaporation gauges. The square-root transformation was used to normalise both the rainfall and pan evaporation data when applying the splines. This ensured more reliable statistical uncertainty estimates and-allowed for a procedure for detecting erroneous data to be established. Investigations were carried out on an empirical model based on accumulated deviations from average rainfall. The model was developed to identify trends in monthly and quarterly average groundwater levels. Model fits were improved using monthly pan evaporation data. A lumped parameter water balance model, previously used for weekly soil moisture index prediction for crop growth, was extended to predict groundwater lev~ls. This model was compared with a lumped parameter monthly water balance model used for streamflow prediction that was extended to predict groundwater levels. In testing the models, hv-block cross-validation was used. The moving-block bootstrap procedure and also uniform grid-search were employed to calculate estimates of uncertainty in the modelling. The extended streamflow prediction model was found to be superior and was efficiently parameterised to accurately model the dynamics of groundwater levels. · The model was found to work accurately in different applications including: determination of recharge patterns over time; use of weekly data and data of different configurations of spatial and temporal interpolations; month-ahead prediction of groundwater levels; prediction of groundwater levels after calibration on streamflow data; prediction of streamflow after calibration on groundwater level data. In addition the model was applied to calculate possible effects of climate change on groundwater level and streamflow. The CSIRO Mk2 Global Climate Model (Hirst et al., 1996; Hirst et al., 1999) was used to estimate the effect of projected climate change on rainfall and pan evaporation in the ACT up to 2030AD under different scenarios. Applying the tested model to the projected climate changes yielded a range of possible groundwater level and streamflow changes in the Orroral Valley, ACT, up to 2030AD. The calculations suggested that there would be no significant change in Orroral Valley groundwater levels or streamflows by 2030AD due to climate change. Suggestions for future research are also discussed.