Case study 5 - Process for dealing with an over-allocated groundwater resource
Background and geographic area
The Padthaway Prescribed Wells Area is located 150 kilometers north of Mount Gambier in South Australia. The area supports significant wine-making and seed-producing industries and has been historically overallocated and faced increased groundwater salinity levels for more than 20 years. To help manage this problem, the Padthaway Groundwater Management Committee was formed in 2002. The Committee, consisting of community and members of the South East Natural Resources Management Board plus staff of the former Department of Water, Land and Biodiversity Conservation (DWLBC), engaged the Padthaway community in the development of recommendations for a new water management plan.
With the use of a three-dimensional computer model of salt and water movement through the area, community and committee representatives participated in setting resource condition limits. A volume of 48,000 megalitres per year was adopted as an acceptable level of extraction. This would provide for the maintenance of resource conditions and protect both groundwater users and the environment.
The Committee's main objective was to provide advice to the South East Natural Resource Management Board (the Board) regarding options for improving water table levels and groundwater salinity in the Padthaway region. Specifically, the Committee aimed to work with the community to develop options for reducing water allocations to an environmentally sustainable level of extraction, while providing for industry and the environment.
Application of a risk–based approach to management
A detailed study was initiated in 2002 by DWLBC to determine the causes of the increasing salinity and identify an acceptable level of groundwater use for the Padthaway region. The study found that a 40 per cent reduction in water allocations was required across the region. It also revealed the two main drivers of salinity increases were clearance of native vegetation and irrigation recycling. Along with this report, a three-dimensional computer model of salt and water movement through the area was developed to help assess risks of different reduction schemes and determine a sustainable level of groundwater extraction.
The Committee worked with the community to run a number of different reduction scenarios through the tool and investigate how certain allocation scenarios would impact their region. Through this process the community agreed that water tables could not be allowed to drop below a certain level and salinity could not increase any further. From this agreed position, an agreement on resource condition limits for the region was made by the community.
Information requirements to achieve objectives
The following information was required:
- The 2002 DWLBC scientific study that investigated the causes of the increasing salinity and identified acceptable ground water usages. This consolidates a number of studies on the salt accession processes and predicted increases in salinity.
- A three dimensional computer model of salt and water movement through the area was developed to help determine a sustainable level of groundwater extraction.
- Scientific data (generated by hydrogeologists and DWLBC / CSIRO scientists) on groundwater ecosystems, their ecological importance and dependence on groundwater.
Approach taken in dealing with uncertainty
The development and usage of the three dimensional model of salt and water movement provided the Committee with a reliable and credible tool to determine risks and outcomes of allocation scenarios. Using this tool, the team:
- set resource condition (threshold) limits, including the maximum acceptable changes in salinity or depth to the water table. The limits established were:
- no increase in the salinity of groundwater
- groundwater tables no lower than the June 2004 levels
- no reduction to lateral through-flow of groundwater through the area (to ensure salts are flushed)
- determined the volume of groundwater that can be extracted on a yearly basis in the area.
Different scenarios were run through the model to determine what level of allocation would result in the conditions of the resource remaining within the agreed limits. It was then decided to:
- provide everybody (active and inactive irrigators) with a minimum allocation
- reduce all allocations, and if some irrigators were using less they were allocated less
- provide the rest of the water to those actively irrigating.
This outcome was accepted by the vast majority of the community. It was then accepted by the Board and recommended to the Minister. The reduction scheme was notable for the high level of community input and direction throughout its development.
Approach taken in consulting with stakeholders
A management plan was developed after an extensive consultation phase with existing water users and other stakeholders (three main rounds of public consultation). The Committee engaged with Board and DWLBC staff, stakeholder groups (Padthaway Grape Growers Association and Padthaway Flood Irrigators Association), DWLBC and CSIRO scientists and the Padthaway community as a whole. The Committee also shared information on its activities through a regular newsletter posted to all licensees and landholders in the Padthaway area. In addition, the proposed method of sustainable use of groundwater was communicated at public meetings and at community consultations.
Community confidence in the science as well as understanding the value of sustainable long-term management of local resources have been the key factors in developing policy for addressing over-allocation. By engaging the community in the planning process, they were able to gain an understanding of the long-term implications of how their water was managed.
The policy satisfies National Water Initiative obligations and provides for the use of the groundwater within ecologically acceptable limits (that is groundwater-dependent ecosystems are protected from declining groundwater levels), while ensuring sufficient water for current irrigation-dependent industry to continue. Seasonal variability in rainfall will be addressed by inputting additional data to the model and periodically determining a new acceptable level of extraction. Changes in the acceptable level of extraction are proposed to be reflected in changes to allocations.
Monitoring and reporting
Each water licence has to provide an annual water use report to the Department for Water, the licensing authority. This includes how much was used and for what purpose. The Department for Water regularly monitors observation wells to monitor trends, salinity and levels.
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