Fact Sheet 12. Intermediate and local flow systems in fractured basaltic rocks and layered sedimentary rocks
Regions
Intermediate and local flow systems in fractured basaltic rocks and layered sedimentary rocks are found in basalt flows and layered sediments of New South Wales, Queensland and South Australia.
Critical attributes that determine groundwater behaviour in response to land management
- Scale: Local and intermediate
- Landform: Plains and undulating terrain
- Aquifer: Fractured basalt; layered sediments - either weathered or fractured
- Aquifer transmissivity: Low _ moderate
- Groundwater salinity: Low _ high
- Land use: Grazing and/or cropping
- Catchment size: Moderate
- Annual rainfall: Moderate
- Salinity manifestation: Drainage depressions
- Salinity rating: S21, S2
- Temporal distribution of recharge: Seasonal with episodic overprinting
- Spatial distribution of recharge: General catchment, higher on upper slopes and crests
- Type areas: Piliga, New South Wales
Discussion
This flow system can be found in either extensive, fractured basaltic materials, or in widespread, sedimentary sequences. In both cases, the characteristic attribute is the layered nature of the system, with higher permeability layers interspersed with layers that restrict groundwater flow. Landscape relief is usually subdued with some regions exhibiting intermediate flow behaviour (i.e. flow passing across catchment boundaries). In other regions flow is more constrained within catchments. Groundwater flow occurs via fractures in basaltic rocks and layered sedimentary rocks. In steeper terrain, groundwater simply flows from individual hills and discharges where the hydraulic gradient reduces in the footslopes. In less steep terrain, groundwater flow may occur over much larger distances, measured in tens of kilometres. Flow may also occur across sub-catchment boundaries. Groundwater discharge and salinity typically occurs where higher permeability fractured rocks rest over less permeable materials, causing groundwater seepages where the interface is exposed in erosional surfaces. Recharge is highest in systems where the fractured rocks outcrop or have minimal soil cover. This form of salinity is particularly common in southern Queensland. The groundwater flow system is not well understood, and further work is needed to identify the most appropriate management options.
Potential options and their suitability for salinity management
Recharge management
Pasture agronomy It is thought that some of these systems are responsive to recharge management, and that this might be achieved through pasture management. Further work is needed to substantiate this position.
Cropland agronomy It is doubtful that manipulation of cropping systems will realise a salinity benefit through recharge reduction.
Woody perennial vegetation (as for pasture management) Woody vegetation may provide a means of managing recharge and realising salinity benefits. Further work is needed for substantiation.
Plantation forestry Rainfall is generally lower than that required for commercial forestry.
Engineering watertable management
Surface drainage Surface drainage may remove water from the landscape that would otherwise become recharge. Further work is needed for substantiation.
Sub-surface drainage Only applicable where circumstances demand the protection of high value assets.
Groundwater pumping Technically feasible and suitable where there is a need to protect high value assets, or where the groundwater is of low or moderate salinity and there are opportunities for its use through small lot irrigation or saline industries.
Managing saline resources
Halophytic vegetation Halophytic vegetation may be suitable in the more arid regions where salinity is higher.
Salt-tolerant grasses/clovers Suited to the higher rainfall regions, where groundwater salinities are lower, and the land is prone to periodic waterlogging.
Saline horticulture & silviculture Opportunities exist for saline horticulture and silviculture, particularly where developments can be irrigated with low to moderate salinity groundwaters.
Salt harvesting Groundwaters are generally not sufficiently saline to make salt harvesting an economic proposition.
Saline aquaculture It is technically feasible in many areas to establish small lot developments for saline aquaculture through groundwater pumping.
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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