Fact Sheet 8. Regional flow systems in alluvial aquifers
Regions
Regional flow systems in alluvial aquifers are found on the riverine plains of Victoria and New South Wales.
Critical attributes that determine groundwater behaviour in response to land management
- Scale: Regional
- Landform: Plains
- Aquifer: Buried alluvial sands and gravels
- Aquifer transmissivity: Very high
- Groundwater salinity: Low - moderate
- Land use: Cereal cropping, grazing
- Catchment size: Very large
- Annual rainfall: Moderate
- Salinity manifestation: Saline depressions and wetlands, vegetation death along stream courses, river salinity increases
- Salinity rating: S2, S3
- Temporal distribution of recharge: Seasonal and episodic
- Spatial distribution of recharge: General catchment but greater within alluvial fans at the highland front
- Type areas: Loddon Plains, north-central Victoria
Discussion
This groundwater flow system typically occurs within many inland alluvial sedimentary sequences (e.g. the Riverine Plain of the southern Murray Darling Basin, and the Plains of the northern rivers of NSW and southern Queensland). The flow system is also recognised in sedimentary basins such as the Perth and Bremer Basins of Western Australia. Groundwater in the Riverine Plains, Murray Darling Basin, is transmitted from upland valleys to the lower plains via very large regional gravel aquifers that lie buried within ancient valleys beneath the sand and clay sediments that make up the Riverine Plains. The regional aquifers are recharged during episodes of sheet flooding on the plains, and through leakage from regional river systems. Recharge is highest within alluvial fans formed near the upland front. Increased recharge, following agricultural development in the down-basin sectors of the plain, results in regional groundwater discharge. Due to the long history of agricultural land use in the southern and wetter regions, groundwater levels have already risen in the upper parts of the catchments, although widespread dryland salinity is yet to be manifest (in the lower parts of the catchments). Rising groundwater levels are yet to be measured in the more arid parts of the flow system. In areas where the groundwater has already been extensively developed, rising groundwater level trends have started to slow. Pertinent management issues for these groundwater flow systems include the:
- existing volume of groundwater due to already increased recharge;
- vast extent across which options must be applied to produce change;
- significant contribution episodic events make to recharge volumes;
- transmissive nature of the aquifers, and the moderate salinity levels of groundwaters.
Potential options and their suitability for salinity management
Recharge management
Pasture agronomy Increased regional groundwater flows are already established through elevated recharge, and will be sustained for a considerable time irrespective of biological management of recharge. Moreover, pasture management will not mitigate recharge produced by sheet flooding episodes nor leakage from regional rivers.
Cropland agronomy As above.
Woody perennial vegetation As above.
Plantation forestry As above, except where plantations are irrigated with water pumped from the regional aquifers.
Engineering watertable management
Surface drainage Drainage may provide some opportunities to remove surface water before it has the opportunity to contribute to recharge, but it is unlikely to manage major recharge events that occur during episodes of sheet flooding.
Sub-surface drainage Sub-surface drainage is technically feasible but only likely to be attractive where there is a need to protect valuable assets. Under these conditions groundwater pumping may also prove to be a more cost effective solution.
Groundwater pumping Groundwater pumping provides considerable opportunities where rising groundwaters are fresh, and capable of being used for small-scale irrigation development. Pumping the more saline groundwaters may also provide significant opportunities for the development of saline industries including saline aquaculture.
Managing saline resources
Halophytic vegetation Halophytic vegetation may prove useful as a means of gaining production from saline soils, particularly in the more westerly regions of the plains where groundwater salinity is higher and the climate is more arid.
Salt-tolerant grasses/clovers Salt-tolerant grasses may have a role in the easterly sections of the plains where salinity effected by groundwater discharge might be less extreme because of lower salinity groundwaters.
Saline horticulture & silviculture Both saline horticulture and silviculture have potential in the Riverine Plains, particularly where they might be irrigated with low to moderate salinity groundwater.
Salt harvesting The high transmissivities of these aquifers means that salt harvesting is technically possible, and will be most suited to those regions where groundwater salinity is highest.
Saline aquaculture Significant opportunities exist, in a technical sense, to extract low to moderate salinity groundwater for the purposes of saline aquaculture.
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
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