Australian Natural Resources Atlas

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Map of local flow systems in fractured rocks

Fact Sheet 4. Local flow systems in deeply weathered fractured rocks

Regions

Local flow systems in deeply weathered fractured rocks are found in the foothills of the Great Dividing Range in Victoria, New South Wales and Queensland, and in the foothills of the Lofty Ranges in South Australia.

Critical attributes that determine groundwater behaviour in response to land management

Discussion

Local groundwater flow systems in deeply weathered fractured rock terrain cause extensive areas of dryland salinity along the foothills of the northern and western slopes of the Dividing Ranges of eastern Australia. These regions are made up of the remnants of early Tertiary land surfaces that have been extensively and variably dissected and eroded. They are typically made up of fractured rock aquifers exposed in the upper slopes and crests of the catchments, which are overlain by remnant clay and weathered bedrock surfaces on the mid and lower slopes. Groundwater recharge is higher on the upper slopes and crests, and lower on the mid and lower slopes. Groundwater migrates from the slopes of catchments toward adjacent valley floors, and is transmitted largely by the underlying fractured rock. Groundwater discharge and salinity typically occur in valley floors and at breaks of slope, and coincident with artesian groundwater pressures caused by reduced hydraulic gradients. In southern Australia these systems occur in landscapes with very high salt stores. Saline groundwater discharges typically cause expansive areas of severe salinity. The issues for managing salinity in these systems are the low permeabilities of aquifers in the lower parts of catchments (and thus the timeframes involved in draining the aquifers sufficiently to lower groundwater levels), the difficulty of locating sustainable groundwater supplies in a hydraulically variable aquifer, and the relatively high groundwater salinity levels.

Potential options and their suitability for salinity management

Recharge management

Pasture agronomy Opportunities for recharge reduction, however salinity benefits unlikely to accrue in less than 50 to 100 years.

Cropland agronomy As above. Some opportunities to incorporate dryland lucerne into cropping rotations, but salinity benefits will not be realised in timeframes of less than 50 to 100 years.

Woody perennial vegetation As above.

Plantation forestry Technically feasible, but poor application because of low rainfall.

Engineering watertable management

Surface drainage May assist with the management of saline soils by controlling run-off and erosion, may also be useful in avoiding salt wash-off from saline soils.

Sub-surface drainage Technically feasible, but only economically sound where there is the need to protect high value assets.

Groundwater pumping As above.

Managing saline resources

Halophytic vegetation Technically suited to high salinity, lower rainfall environs. Sometimes used as pioneer species to assist establishment of less salt-tolerant pastures.

Salt-tolerant grasses/clovers Largely restricted to less saline lands.

Saline horticulture & silviculture Poorly suited to high salinity poorly drained soils.

Salt harvesting Technically feasible but limited somewhat by the difficulty in locating suitable groundwater yields.

Saline aquaculture Technically feasible where the economic environment is favourable.

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

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