Upper Billabong Creek Case Study Catchment, New South Wales
The Upper Billabong Creek catchment is in New South Wales, between the Murrumbidgee and Murray Rivers. The catchment is predominantly cleared on the lower slopes. Land use is dominated by grazing, with some cropping, particularly on the alluvial flats. Small, break-of-slope expressions of salinity are found in the local to intermediate flow systems of the Palaeozoic rocks in the upper parts of the catchment.
Despite the low permeabilities, the generally good water quality in these systems means that waterlogging rather than salinity will be the major issue. These flow systems connect to a regional alluvial system in the lower parts of the catchment where the high permeabilities and low to moderate groundwater gradients mean that the catchment has a moderate to high ability to move groundwater.
The flow system of the lower parts of the catchment is common in the Riverine Plains in NSW and Victoria.
Approximately 140 ha (or less than 1% of the catchment area) have surface expression of dryland salinity, as part of the local to intermediate flow system. There is no sign of saline discharge related to rising regional groundwater systems.
Figure 25.Distribution of intermediate and local groundwater flow systems in fractured rocks.
Results of groundwater investigations and modelling
The groundwater investigation suggests that although groundwater movement through the lower parts of the catchment is reasonably fast, its response to extensive changes in land use is expected to be slow (due to the regional scale of the flow system).
- If the current land use is maintained, groundwater levels will reach the surface at break of slope and on the plains in about 50 years; less than 2% (~5000 ha) of the catchment is predicted to be at risk from shallow watertables and salinity.
- If recharge in the catchment is reduced by 50%, the watertable will continue to rise, albeit more slowly, and affect a similar area of land as the `do nothing' scenario after about 100 years.
- If recharge in the catchment is reduced by 90%, groundwater levels will continue to rise, but the system will stabilise before the watertables become shallow enough to cause salinity.
Implications
- In the Billabong catchment, carefully delineated recharge areas can be targeted if recharge control is part of an overall strategy.
- Strategic groundwater pumping with current levels of recharge can delay the rise of water levels by up to 50 years and reduce groundwater heads by up to 1 m compared with the `do nothing' scenario.
Figure 26and Table 23.Upper Billabong (New South Wales): change of area at risk in response to different recharge reduction rates - based on current recharge rate.
|
Recharge Reduction |
|||
|
Year |
No change (%) |
50% |
90% |
|
2000 |
0.0 |
0.0 |
0.0 |
|
2020 |
0.2 |
0.0 |
0.0 |
|
2050 |
1.3 |
0.8 |
0.0 |
|
2100 |
1.6 |
1.3 |
0.0 |
CAPACITY TO CHANGE - Upper Billabong case study of dryland salinity and watertable control
Upper Billabong Creek catchment, located NW of Holbrook (NSW) in the Murray Darling basin. At present much less than one per cent of the catchment is salinised and CSIRO believes that, even without management, this will increase only to about one per cent over the next 50 years. The salt load exported from the Upper Billabong Creek catchment contributes only a very small part of the water quality problems at the bottom end of the Murray River.
Background
The analysis compared the benefits and costs associated with salinity control in Upper Billabong catchment being one of four contrasting case studies (Kamarooka, Lake Warden, Wanilla). The approach adopted was to take estimates of the physical scale of impacts for each type of damage caused by dryland salinity (e.g. area of agricultural enterprises, number of stream diverters, kilometres of roads affected, number of species affected), and to apply damage functions for each of those types of impact. Data describing the physical scale of impacts have been captured using mainly GIS layers which describe the location of dryland salinity in each case study catchment. The damage functions developed for the purposes of quantifying the economic impacts of dryland salinity are for: agriculture and commercial forestry; roads and rail; urban centres; water users; and environmental values.
Key findings
- For the Upper Billabong Creek catchment (NSW) case study it was concluded
that, even without management, the extent of dryland salinity would expand
only to about one per cent of the catchment area over the next 50 years. The
present salt load in surface flows has attracted attention, but the impacts
are relatively small in absolute terms. The present load from Upper Billabong
Creek of 310 tonne salt per year is estimated to increase the salinity at
Morgan by 0.085 EC (µS/cm) at a cost to consumers of approximately $13,000
per annum in additional costs and reduced outputs.
- We have estimated that the present impacts from dryland salinity in the
Upper Billabong Creek catchment would be approximately $40,000 per year, comprising
losses in agricultural production of $22,500 per year, impacts for downstream
water users of $13,000 per year and impacts for roads of $2,000 per year.
- Rainfall varies significantly across the catchment and the economic analysis
of tree planting indicates that most landholders would face reductions in
income, but some landholders with higher rainfall in the upper catchment could
achieve increases in income over the longer term with tree planting. Given
that the benefit would comprise only the avoidance of salinisation for about
one per cent of the catchment area, there would not be a great incentive for
landholders in the catchment to adopt radical and extensive land use change
over much of the area.
- Neither the in-catchment benefits, nor the downstream impacts for water
users, are anywhere near large enough to justify substantial expenditure for
salinity control in the Upper Billabong Creek catchment. However, water quality
for downstream users, particularly in Adelaide, may still warrant some attention.
With a substantial part of the total salt load of the Murray Darling basin
coming from a very large area, it is not a sound economic investment to treat
the salt at its source; that is, in upstream catchments, like the Upper Billabong
Creek, which have only a relatively minor salinity problem within the catchment.
To the extent that water quality for downstream users does warrant some attention,
then this is likely to involve water treatment at the lower end of the catchment.
- Upper Billabong Creek is perhaps the most instructive case study. An investment in improved understanding of catchment processes has revealed a far lesser salinity problem than initially expected on the basis of limited monitoring and best bet understandings of salinity process. This underlines the importance of reliable science based understandings of regional salinity as a foundation for public investment decisions.
Lessons learnt from all salinity case studies:
- There is no simple broadly applicable paradigm with which to conceive our
responses to salinity.
- Expectations of farm based change leading to salinity control need to be
tempered.
- Broad scale reforestation proposals will often be poor investments from
an economic and social perspective.
- A lack of profitable technically feasible options is the major constraint
to the capacity to control salinity.
- The major issue of "capacity for change" is the capacity of our
community to make informed decisions about investment in salinity control.
- We need to re-engineer our integrated catchment management structures to
operate within an adaptive management framework.
- Investment in salinity control should be based upon a triage model.
- A "works on the ground now" imperative should be tempered by a
"least regrets" investment approach.
- Landscape change must be seen as a multi-generational challenge.
Further Information
the technical reports:
Please Note: PDF files are in Adobe Acrobat Version 4.0 format. You will need a copy of an Acrobat Reader in order to view them. Blind and visually impaired users can view.pdf files using a tool available on-line from Adobe Systems that converts the.pdf files on the fly to HTML.
- Assessment of Salinity Management Options for Upper Billabong Creek Catchment, NSW: Groundwater and Farming Systems Water Balance Modelling - REPORT in PDF format (0.5 MB)
- Assessment of Salinity Management Options for Upper Billabong Creek Catchment, NSW: Groundwater and Farming Systems Water Balance Modelling - APPENDICES in PDF format (0.9 MB)
- Capacity to change - Case studies of dryland salinity and watertable control by Mike Read. PDF format (1.2 MB)
- Capacity to change - Case studies of dryland salinity and watertable control - APPENDICES by Mike Read. PDF format (1.9 MB)
- Structural Change in Australian Agriculture: Implications for Natural Resource Management: Salinity case studies by Neil Barr. PDF format (1.3 MB)
Table of Contents for the Australian Dryland Salinity Assessment 2000
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