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Abstract
In semi-arid environments, groundwater provides the basis for ecosystems and human activity. While groundwater responds to large flow events and recharge is thought to occur predominantly via stream channels (i.e., focused recharge), little is known about its spatio-temporal characteristics and how it relates to effective water resource management.
This study aims to identify the dominant groundwater recharge mechanisms and the extent of resource recovery following a climatic transition from dry to wet in the Maules Creek Catchment, New South Wales, Australia. The dynamic interactions between streamflow and groundwater levels were analysed using 15- to 30-minute resolution data at three representative sites along intermittent and perennial stream channels. At the catchment scale, long-term trends in groundwater level have been analysed using monthly records collected from 35 monitoring bores since the 1980s.
The site and catchment scale analyses demonstrate the following:
(1) In the intermittent section, groundwater level drawdown of up to 5 m was recovered to near or above pre-irrigation (~1980) levels.
(2) Along the intermittent stream reaches, groundwater recharge depends on antecedent groundwater level and soil moisture conditions.
(3) Episodic high stream stage events provide limited recharge to perennial stream reaches since rises in stream stage mainly cause temporal bank storage. Groundwater level increases near these perennial reaches are consequently due to this bank storage and due to loading effects occurring on a time scale of weeks to months.
(4) Areas away from stream channels exhibited an overall decline and the groundwater resource was not restored to pre-abstraction conditions.
This thesis demonstrates that ephemeral and intermittent streams may exhibit significant focused recharge relative to the diffuse recharge over the catchment; whereas, aquifers along perennial streams can only temporarily store water because these streams generally act as groundwater drains. Streams can dynamically behave as ephemeral, intermittent or perennial depending on the longer-term climate-groundwater interaction. Consequently, hydrologic classification of stream reaches in semi-arid areas must allow for dynamic changes and account for the connection to groundwater. This thesis further highlights the potential for managed aquifer recharge along ephemeral and intermittent streams to better utilise stormflow and, therefore, to drought-proof rural communities.