Fact Sheet 2. Intermediate flow systems within sedimentary sequences infilling large valleys
Regions
Intermediate flow systems within sedimentary sequences infilling large valleys are found in the wheat belt of Western Australia.
Critical attributes that determine groundwater behaviour in response to land management
- Scale: Intermediate
- Landform: Alluvial plains within broad valleys
- Aquifer: Alluvial sediments
- Aquifer transmissivity: Low - high
- Groundwater salinity: High
- Land use: Cereal cropping
- Catchment size: Large
- Annual rainfall: Low
- Salinity manifestation: Expansive areas in valley floors
- Salinity rating: S3
- Temporal distribution of recharge: Seasonal with strong episodic overprinting
- Spatial distribution of recharge: General catchment
- Type areas: Toolibin, eastern wheat belt of Western Australia
Discussion
This groundwater flow system is made up of ancient valleys that once formed an integrated river basin draining the south-west of Western Australia. The old valleys were extensively disrupted by tectonic activity during Tertiary times, and have been infilled with both coarse and fine-grained alluvium. Each ancient river basin now forms a series of discrete, elongate linear groundwater basins that may be contiguous over distances of 10 to 20 km or more. The alluvial fill in the valleys forms the main aquifer and the groundwater it contains is extremely saline. Groundwater recharged on the slopes of the broad valleys converges on these unconfined/semi-confined transmissive aquifers in the plains of the valley floors. Salinity is manifest as expansive areas of saline groundwater discharge within these linear plains. The diffuse and episodic nature of recharge means that it is extremely difficult to manage recharge rates using conventional farming systems. Although transmissivity rates are variable in these aquifers, engineering options are theoretically feasible, but the high salinity of groundwaters controls the potential uses for extracted groundwaters.
Potential options and their suitability for salinity management
Recharge management
Pasture agronomy These groundwater systems are not responsive to recharge management due to the diffuse and episodic nature of recharge, but benefits can be achieved at the farm or sub-catchment scale.
Cropland agronomy As above.
Woody perennial vegetation As above.
Plantation forestry As above.
Engineering watertable management
Surface drainage May be appropriate in areas where it can be used to avoid waterlogging and exacerbation of salinity.
Sub-surface drainage Technically feasible and appropriate, particularly where there are important high value assets that must be protected. The high salinities of groundwaters must be taken into account in disposal/utilisation options.
Groundwater pumping As above.
Managing saline resources
Halophytic vegetation Technically feasible and appropriate in semi-arid environs. Also used as a pioneer species to assist establishment of less salt-tolerant pastures.
Salt-tolerant grasses/clovers Poor application in areas with high salinity and aridity (unless used as above).
Saline horticulture & silviculture Generally excessively saline conditions.
Salt harvesting, saline aquaculture Technically feasible, but largely dependant upon economic circumstances.
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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