Australian Natural Resources Atlas

Natural Resource Topics

Map of intermediate flow systems in fractured rock aquifers

Fact Sheet 6. Intermediate flow systems in fractured rock aquifers

Regions

Intermediate flow systems in fractured rock aquifersare found in more gentle hilly terrain of the uplands of the Great Dividing Ranges in eastern Australia.

Critical attributes that determine groundwater behaviour in response to land management

Discussion

Fractured rock aquifers commonly influence dryland salinity in the Great Dividing Range of eastern Australia. These intermediate groundwater flow systems occur where the slopes of the land are not excessive, and where local relief is generally less than 20-30 m. Under these circumstances groundwaters may flow across catchment boundaries. Groundwater recharge typically occurs in regions where fractured rock outcrops occur in catchment headwaters. Groundwater flows down basin over distances of 20-30 km or more, and discharges where there is a reduction in the hydraulic gradient consistent with major changes in slope of the land. This commonly occurs immediately below catchment headwaters. Salinity frequently occurs within the mid to upper catchment regions. Groundwater discharge most commonly occurs through baseflow to streams, often contributing as much as 600 kg of salt per hectare of catchment to downstream rivers. The issues for managing these systems relate to the scale at which options must be applied; the moderate groundwater salinity levels (2000-6000 mg/L); and the timeframes required for aquifers to drain sufficiently to lower groundwater levels.

Potential options and their suitability for salinity management

Recharge management

Pasture agronomy Deeper-rooted pastures may reduce recharge, but it is unlikely that recharge can be reduced to the levels required to restore pre-development rates by this means alone (especially in the more winter-dominated regions). In addition, the groundwater systems are highly buffered against groundwater level change by the large dimension of the aquifer.

Cropland agronomy Little cropping is practised in this terrain, and groundwater flow is strongly buffered by existing conditions.

Woody perennial vegetation Applications may be useful in reducing recharge but groundwater systems are strongly buffered against change.

Plantation forestry Plantation forestry is effective in reducing recharge, but strongly buffered groundwater systems will militate against short-term salinity benefits. Reduction in surface water run-off as a consequence of plantation developments is also likely to exacerbate stream salinity in the short to medium term.

Engineering watertable management

Surface drainage May be beneficial in reducing surface water moving over salt-affected soils, thus protecting saline soils from soil erosion.

Sub-surface drainage May be used to protect high value assets, but groundwater pumping will usually provide greater benefits and be more cost-effective.

Groundwater pumping Technically feasible where high value assets must be protected, or where moderately saline groundwater might be used as an industry resource.

Managing saline resources

Halophytic vegetation Higher annual rainfall and ephemeral waterlogging are not generally conducive to halophytic vegetation.

Salt-tolerant grasses/clovers Salt-tolerant grasses have widespread application for maintaining vegetative cover and a measure of agricultural productivity on saline soils within upland areas.

Saline horticulture & silviculture A limited range of productive species can be grown on saline land in upland areas.

Salt harvesting Low to moderate salinity groundwater and higher ratios of precipitation/evaporation generally make this option less feasible.

Saline aquaculture Considerable potential exists for low to moderate salinity groundwater to be used in commercial aquaculture, as long as appropriate means of managing salt and nutrient disposal can be secured.

Combining options

The use of two or more of the above options (appropriate to the prevailing climate, soil type and landscape position) typically may have a beneficial salinity management effect.


Table of Contents for the Australian Dryland Salinity Assessment 2000

Next Section

Previous Section

Before you download

Most publications are downloadable as PDF files. Adobe Acrobat Reader  is required to view PDF files.

If you are unable to access a publication, please contact us to organise a suitable alternative format.

Key

   Links to an another web site
   Opens a pop-up window