Salinity - Management - Queensland
Queensland
Introduction
Treating the cause of salinity through recharge reduction may be effective in reversing salinisation in only a few responsive groundwater systems. Once the salinisation process is under way it is extremely difficult to slow, halt or reverse in order to protect water and land resources. Prevention is a far better investment than any attempt at control or management.
Northern Australia presents opportunities to avoid the dryland salinity problems of temperate Australia. Broad-scale clearing without recognition of salt stores and the resulting change in water balance is a recipe for problems, whether it is in 20 or 100 years. Wise management now to protect the landscape and prevent dryland salinity will prove far more cost-effective than any attempts to solve the problem once it occurs.
While salinity analysis has focused on southern Australia, sound scientific evidence (Bui et al. 1996, Williams et al. 1997, Bui 2000, Gordon et al. 2000, Gunn1967, Shaw et al. 1994) shows that all the factors that contribute to salinity hazard also exist over large areas of the semi-arid zones of northern Australia. Two factors that must be present for a salinity hazard to exist after clearing or change in vegetation cover are :
- presence of stored salt in the soil, regolith or groundwater systems, and
- an increase in the water draining beneath the root zone following tree clearing or vegetation change.
Water balance
As the groundwater system fills and eventually reaches a new equilibrium, the amount of water entering the landscape as recharge and the amount of water leaving as discharge is balanced. However there is a time lag between when changes in land use or improvement in water balance occurs and evidence of a response. It will take decades to reverse the water rise in most groundwater systems (see figure below).
Re-establishing the water balance requires farming systems with similar water use to that of deep-rooted native vegetation. Designing and implementing such farming systems is a major challenge.
Recharge processes are generally faster than discharge processes. If it takes 30 to 50 years for our fastest groundwater system to fill with water, then it is reasonable to expect that it might take at least 30 to 50 years for it to empty back to where it was. If the system takes 100 years or more to fill, we can again expect at least a similar amount of time to establish the original equilibrium. This is an important issue for management as the degree of recharge reduction and the time taken have important consequences on land use options during any adjustment period, and the degree of change sought. Beneficial effects of land use options may well occur before the system has returned to an equilibrium.
Salt balance
As more water moves through an aquifer, more salt is mobilised. Very long periods of time are needed for catchment salt stores to be reduced to the point where the amount entering the system equals the amount leaving the system, that is, to achieve a salt balance. The net amount of salt that exits a catchment via stream flow indicates the time it will take for the catchment to flush its store of salt, when compared with the total mass of salt stored in that catchment. In some of the more responsive groundwater flow systems, the net output of salt may take about 150 years to flush from the system. In larger catchments (e.g. the Murray groundwater basin), it may take as much as 15 000 years. This means that although management may lower the watertable and allow productive use of land, there may be ongoing salt inflow to streams via groundwater.
This makes managing stream salinity very difficult. It is very important to prevent the interception of groundwater with salt stores in regions where we still have this opportunity.
The reality
The substantial lag times for catchments to come back into water balance and change salt mobilisation mean that it is inevitable that dryland salinity will be a feature of many Australian landscapes for some time. This is true even with widespread adoption of innovative land uses that manage to turn off the recharge tap and re-establish water balance. Ultimately the decisions on the measures to be taken will be influenced by the value of the threatened assets, the capacity to manipulate the environmental processes, the economic feasibility and social acceptance of the proposed actions.
What is the scale of the groundwater systems and how can they be managed?
Groundwater trends
The Condamine-Balonne and Border Rivers catchments are the only catchments in the State where sufficient data exist to determine, on a catchment-wide basis and with a moderate level of accuracy, the area with groundwater levels within 2 m of the surface (some 17 500 ha).
More detailed information is available in the Queensland Dryland Assessment 2000 Report
The groundwater flow systems for Queensland are present in the table below. Within the >300mm rainfall zone, 123,000 hectares in local, 1,473,000 hectares in intermediate and 1,468,000 hectares in regional flow systems are coincident with regions within which there are areas with a high hazard of dryland salinity.
| Groundwater Flow System Type | Area (ha) at risk in 2050 | Percentage of total risk area (%) |
|---|---|---|
| Local and intermediate flow systems in deeply weathered rocks | 47,633 | 2 |
| Intermediate flow systems in sedimentary sequences in large valleys | 68,431 | 2 |
| Local flow systems in fractured or weathered rocks or colluvial fans | 73,250 | 2 |
| Intermediate flow systems in fractured rocks | 964,581 | 31 |
| Local flow systems in fine grained unconsolidated sediments | 2,144 | 0 |
| Regional flow systems in permeable alluvial sediments | 240,869 | 8 |
| Regional and intermediate flow systems in fractured basaltic rocks and layered sedimentary rocks | 1,227,444 | 40 |
| Intermediate and local flow systems in fractured basaltic rocks and layered sedimentary rocks | 439,894 | 14 |
* Area within >300mm rainfall zone
Government responses to dryland salinity as at the year 2000
Government response
This assessment has resulted in the first State-wide hazard assessment of dryland salinity in Queensland. It has identified a significant long-term risk associated with dryland salinity in Queensland and will assist in setting priorities for investigations, assessments and development of management responses on dryland salinity.
Several natural resource management initiatives have recently been implemented within Queensland and contain specific actions to minimise the future risk of dryland salinity. The Queensland Government has enacted the Vegetation Management Act 1999 (Qld) to provide controls over the clearing of remnant vegetation on freehold land to complement the Land Act 1994 (Qld) that covers leasehold land. The provisions of the Act include the preparation of regional vegetation management plans and the assessment of applications for the clearing of remnant vegetation. The accompanying policy and assessment code provides for the protection of vegetation in areas susceptible to salinisation. The Water Act 2000 (Qld) includes provisions for the preparation of property-level plans and district water use plans to address land and water management issues associated with irrigation water use including salinisation and rising groundwater levels.
Salinity outbreaks are generally localised and technical assistance is provided through government in planning control options on an individual or group basis. Numerous dryland salinity projects have been implemented with the support of Landcare and integrated catchment management groups throughout Queensland (e.g. the Balfes Creek catchment in North Queensland was a focus catchment for dryland salinity research under the National Dryland Salinity Program).
A review of the information needs for assessing and monitoring of dryland salinity has been completed in conjunction with this Audit. The review includes a work plan that will significantly increase the knowledge base on salinity and provide the technical support to underpin government policy initiatives in land and water management, and vegetation clearing. Work is being undertaken to refine salinity risk assessment in Queensland in key regions utilising the groundwater flow system approach as the framework. Implementation of the salinity work plan will be considered as part of Queensland?s response to the Commonwealth?s National Action Plan for Salinity and Water Quality.
Further information
- Queensland Dryland Salinity Assessment 2000 report
- Australian Dryland Salinity Assessment 2000 report
- National Technical Overview Report of the State-based dryland salinity assessments
- Australian Groundwater Flow Systems Report
- Queensland Department of Natural Resources
- National Dryland Salinity Program
- National Action Plan for Salinity and Water Quality
Link to Map maker to make a map using this information.
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