1.1.4.3 Groundwater flow

The main regional groundwater fluxes in the Hunter subregion largely follow topography, from the upland towards the river channels with overall discharge towards the ocean.

Groundwater recharge mechanisms include:

recharge predominately from rainfall, the volume of which is commonly estimated as less than 2% of annual rainfall with higher values associated with the areas of regolith permeability (e.g. in the anticline zones) (Mackie Environmental Research, 2006). Watertables and pressures in the coal measures appear to be sustained by rainfall percolation into out-cropping strata at a generally low rate
localised recharge to alluvial aquifers, mainly associated with natural river flow during rainfall events and particularly during flooding. This is also supplemented by leakage or environmental water releases from water supply dams (e.g. Glenbawn or Liddell dams)
upward fluxes from fractured rock aquifers to alluvial aquifers, which can also lead to high salinity in rivers during baseflow periods.

Recharge to groundwater systems generally occurs in areas where the regolith is well developed or where alluvial deposits have accumulated. The largest portion of recharge to the main alluvial aquifer system is driven by rainfall in the upper catchments rather than local rainfall. Due to a lower permeability of the upper alluvial layers a large streamflow event or a series of events are required to cause significant recharge in the aquifer systems. The effect of a recharge mound can be observed 60 to 800 m from the stream. In areas where floodplains exist recharge is greater.

Groundwater discharge mechanisms include:

upward fluxes from fractured rock aquifers to alluvial aquifers, particularly in areas where Permian fractured rock aquifers occur
Permian groundwater discharge as springs and seepage to watercourses
discharge from alluvial aquifers forms river baseflow throughout the subregion, which is more consistent in the main Hunter alluvial systems and less consistent in the elevated areas (NSW Department of Planning, 2005)
groundwater abstraction for irrigation and other purposes, which is particularly significant during dry seasons or drought periods
ultimately groundwater from the Hunter subregion is discharging to the ocean, which includes submarine discharge along the coast.

In the headwater regions (e.g. the Goulburn River catchment) baseflow ceases approximately 10 to 20% of the time. However even during such periods water remains in the creeks as disconnected pools which provide refuge and as such are critical habitat for aquatic species (NSW Department of Planning, 2005). To ensure environmental flow requirements are met, ‘Cease to Pump’ conditions exist in a number of regional water sharing plans, which define thresholds of minimal river flow (e.g. in the Wybong Creek this threshold is 0.5 ML/day).

Last updated:

18 January 2019

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