Historic groundwater level changes in the Georgina Basin

The aim of this study was to identify water level changes in the northern Georgina Basin aquifers over time and if present to relate them to possible causes. There are no groundwater monitoring boreholes within the Northern Territory portion of the Georgina Basin, which limits information on groundwater levels. For most private boreholes, groundwater levels have been recorded upon the completion of the bore construction process. At locations where at a later date a new or replacement bore has been constructed in relatively close proximity to existing bore(s), an insight can be gained into how groundwater levels may have changed over time, and may elucidate trends over periods of decades. A preliminary analysis of groundwater levels records was conducted to identify general trends. Rainfall records from the Bureau of Meteorology (BOM), in addition to groundwater levels from the Department of Environment and Natural Resources (DENR) monitoring bores surrounding the Basin, were inspected to determine periods of above- average annual rainfall which may have led to rises in groundwater levels. Groundwater recharge in the basin is very sporadic, restricted to times of exceptional rainfall, punctuated by up to decades of little or no recharge. Findings of the analysis show that standing water levels (SWL) of bores established in the Georgina Basin cover periods of above- and below-average rainfall and a comparison of SWLs at locations where consecutive measurements were taken indicates that water levels generally rose over multiple high rainfall events. Due to the paucity of SWL data in the basin, the confidence levels in these results are relatively low. No assessment of accuracy and error margins was performed. Long term rainfall records compared to bore hydrographs from outside the basin suggest that recharge is very sporadic, restricted to times of exceptional rainfall, punctuated by up to decades of little or no recharge. Further statistical analysis may be relevant to determine the significance of initial results.