Fact Sheet 7. Local flow systems in fine grained unconsolidated sediments
Regions
Local flow systems in fine grained unconsolidated sediments are found in south-west Victoria.
Critical attributes that determine groundwater behaviour in response to land management
- Scale: Local
- Landform: Dissected clay plateaus
- Aquifer: Clay deposits
- Aquifer transmissivity: Low
- Groundwater salinity: Low - moderate
- Land use: Grazing
- Catchment size: Small
- Annual rainfall: Moderate
- Salinity manifestation: Break of slope and valley floor
- Salinity rating: S1, S2
- Temporal distribution of recharge: Seasonal
- Spatial distribution of recharge: Recharge occurs diffusely over the entire catchment
- Type areas: Barwon Downs & Heytsbury, Victoria
Discussion
Dryland salinity is particularly common in these low permeability landscapes that have a moderate to high salt store, particularly where the climate imposes cold wet winters and hot dry summers. These conditions are found in landscapes made up of marine clay deposits within the Heytsbury_Barwon Downs region of south-west Victoria. Local flow systems develop in the low permeability clays as a consequence of recharge on the slopes and crests of a catchment. Groundwater discharge occurs at breaks of slope or on adjacent valley floors. The main issue for managing dryland salinity in these systems relates to the low permeability of the aquifers, and thus their limited ability to drain sufficiently to lower groundwater levels.
Potential options and their suitability for salinity management
Recharge management
Pasture agronomy Elevated groundwater and poorly responsive aquifers will sustain groundwater convergence on saline areas long after recharge management is applied.
Cropland agronomy Poor aquifer responsiveness and little ability to manipulate recharge within cropland management.
Woody perennial vegetation Poorly responsive aquifers and large areas of farmland needed for effective recharge management.
Plantation forestry Opportunities for recharge management, but unlikely to yield significant salinity benefits within the short to medium term because of poorly responsive aquifers. Plantation forestry would also compete with high value agricultural lands.
Engineering watertable management
Surface drainage Surface drainage does provide some opportunities to remove surface water before it has the opportunity to become recharge. The practice is unlikely to yield salinity benefits within the short to medium timeframes.
Sub-surface drainage Low permeability landscapes make this option more difficult to apply. It will generally be applicable only in those regions where it is essential to protect high value assets.
Groundwater pumping Low permeability landscapes provide little opportunity for groundwater pumping, although it may be technically feasible where it necessary to protect high value assets.
Managing saline resources
Halophytic vegetation Halophytic vegetation is more suited to semi-arid regions less prone to cold wet winters and waterlogged soils.
Salt-tolerant grasses/clovers Salt-tolerant grasses are well suited to saline soils within these groundwater flow systems.
Saline horticulture & silviculture Horticulture is generally less suitable due to heavy soils prone to waterlogging. There may be opportunities for saline silviculture where native species can be utilised.
Salt harvesting Groundwaters are generally too fresh for salt harvesting to be an economic proposition.
Saline aquaculture Insufficient groundwater to make saline aquaculture technically feasible.
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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