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Abstract
A groundwater recharge investigation in the arid zone of Australia is presented. The investigation used a wide range of hydrogeological techniques including geological mapping, surface and borehole geophysics, groundwater hydraulics, streambed temperature and pressure monitoring, and hydrogeochemical and environmental tracer sampling, and it was complemented by analysis of rainfall intensity from 18 tipping-bucked rain gauges, climate data and stream runoff measurements. Run-off and recharge from a 200-mm rainfall event in January 2015, the largest daily rainfall in the local 50-year record, were investigated in detail. While this major storm provided substantial run-off as a potential source for focused, indirect recharge, it only produced enough actual recharge to the shallow aquifer to temporarily halt a long-term groundwater recession. A series of smaller rainfall-runoff events in 2016 produced a similar recharge response. The results suggest that the total magnitude of a flood event is not the main control on indirect groundwater recharge at this location. A deeper aquifer shows no hydraulic response to surface-water flow events and is isolated from the shallow system, consistent with its Pleistocene groundwater age. This supports a growing body of evidence indicating that attributing or predicting generalised changes in recharge to changes in climate in dryland environments should not be attempted without first unravelling the dynamic processes governing groundwater recharge in the locality of interest. The results should prompt more detailed and long-term field investigation in other arid zone locations to further understand the episodic and nonlinear nature of recharge in such environments.
Highlights
Groundwater recharge in drylands is thought to occur increasingly by ‘focused’ means as aridity increases (De Vries and Simmers 2002, Lerner et al 1990)
At Fowlers Gap in the semi-arid zone of western New South Wales, Australia, the rainfall and runoff in a 460 km2 catchment has been investigated in detail using a range of integrated hydrological and hydrogeological methods that have included installation of a tipping-bucket rainfall monitoring system of 18 gauges, a climate station, runoff monitoring, geological investigation, installation of groundwater monitoring boreholes, surface geophysics, stream bed thermal and pressure analysis, downhole geophysical logging, hydrochemical analysis and interpretation using water chemistry and environmental isotopes
The monitoring equipment was installed in time to monitor the response of the catchment to the most extreme 36-h rainfall event recorded in the past 50 years during January 2015
Summary
Groundwater recharge in drylands is thought to occur increasingly by ‘focused’ means as aridity increases (De Vries and Simmers 2002, Lerner et al 1990). Runoff in the arid zone commonly occurs as a result of extreme rainfall events, often the result of exceptional storms Under such circumstances, monitoring infrastructure, if present, often fails or is destroyed, often leaving only estimates of runoff occurrence, rainfall distribution and general assumptions concerning groundwater recharge. Such monitoring challenges (Pilgrim et al 1988) can curtail the development of models from which to estimate runoff and Hydrogeol J (2021) 29:737–764 groundwater recharge. More recently there have been significant steps forward in field-based research to quantify focussed recharge in drylands and a brief review follows
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