Case study 6 - Managing complex existing user issues and different user groups for groundwater and surface water

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Geographic area

Marne and Saunders catchments lie on the western rim of the Murray-Darling Basin in South Australia, about 70 kilometres north east of Adelaide.

Objective

Set sustainable extraction limits and water taking rules for newly prescribed water resources (surface water, watercourses and groundwater), with consideration of:

  • balancing social, economic and environmental water needs, including existing user rights
  • surface water – groundwater interactions and sharing water between users of linked resources
  • accounting for interception and use of water for stock and domestic purposes
  • protecting users, including the environment, from impacts of new or transferred water use.

The Marne and Saunders catchments are on the slopes of the Eastern Mount Lofty Ranges; the rivers flow through gorges onto the Murray Plains and then into the River Murray. The watercourses in the ranges flow seasonally in response to winter and spring rainfall and contract back to permanent pools in summer and autumn. These pools provide important refuge habitats for aquatic organisms and are commonly maintained by groundwater inflow. Rainfall is low on the Murray Plains, and almost all of the streamflow in this area comes from the wetter ranges. This flow provides almost all of the recharge to the underlying groundwater aquifer, which in turn provides most of the water used in the region for stock use and irrigation, particularly lucerne, turf and olives.

There is significant farm dam development in the ranges, largely for irrigation (particularly wine grapes), stock and domestic purposes. Flow modelling shows that dam development has decreased the average annual stream flow by almost 25 per cent, reducing the volume flowing down stream to recharge the aquifers on the plains. This has led to tension between communities in the ranges and plains as they try to resolve issues around water sharing. The tension is exacerbated by perceived differences in the value of water-using purposes between the regions. There are also concerns about water sharing at a local scale, such as impacts of dams and groundwater pumping on neighbours.

Water extraction and interception have also affected water-dependent ecosystems. Groundwater extraction has the potential to reduce input of baseflow to watercourses and may lower groundwater tables beyond the reach of deep-rooted vegetation. Dam development affects the flow volume as well as environmentally important parts of the flow regime. When the water level in a dam is low, the dam will capture all flow until the dam fills and spills over. Flow modelling in the catchments shows that dams are likely to intercept much of the flow over summer and autumn; they also delay break-of-season flows in early winter. Refuge pools are then at greater risk from becoming too salty or hot or even drying out altogether. The shortened flow season means that there may not be water available for a sufficient period of time for aquatic plants and animals to complete their lifecycles.

Application of a risk–based approach to management

Some of the major risks associated with water extraction and the management approaches include:

  • interception of environmentally important low to medium flows by dams
  • managing the impact of groundwater level drawdown on users and the environment
  • accounting for environment, existing user rights, water availability and non-licensed interception
  • sharing available water between the ranges and plains.

Interception of environmentally important low to medium flows by dams

Surface water models were used to assess the likely effect of current dams and different water management options on the extent to which environmental flow targets could be achieved. It was found that managing only the usage from dams would not achieve the targets. Reducing existing dam capacities was seen as the least socially acceptable option by the community based water planning committee. The modelling showed that returning low flows (below a defined threshold flow rate) around existing licensed dams achieved the targets when used in combination with managing the volume taken from dams.

Low flows can be returned using 'low flow bypasses', which are mechanical devices that can be fitted to dams and watercourse diversions to allow flows below a given flow rate to pass around a dam back into the watercourse downstream, while flows above that rate can pass into the dam. Several examples of low-flow bypasses are described in construction guidelines at Natural Resources SA Murray-Darling Basin .

This approach was seen as the best way of sharing water between existing users and the environment, by allowing critical low flows to return to the environment while allowing users to harvest a share of the higher flows.

Managing the impact of groundwater level drawdown on users and the environment

Regional drawdown of groundwater levels was addressed by setting groundwater extraction limits that balance groundwater water input (recharge) against output (baseflow, throughflow to other aquifers, licensed and non-licensed use). All of the estimated volumes of baseflow, throughflow and non-licensed use have been subtracted from the long-term average recharge when setting the annual volume available for licensed extraction. Groundwater models were used to set extraction limits that would keep the groundwater levels within acceptable ranges to:

  • avoid permanent groundwater level drawdown and therefore reduce the risk of drawing in saline groundwater from adjacent areas
  • maintain groundwater levels within the range thought to be accessible by deep-rooted vegetation

The major source of recharge to the major aquifer on the plains is streamflow. Modelling of this aquifer used streamflow conditions that had been generated under average-to-dry conditions to replicate this connection and to manage water conservatively.

At a local level, future impacts on users and the environment are managed using buffer zones around bores and groundwater-dependent ecosystems. New bores (including stock and domestic) and transfers are generally not permitted where the buffer around that bore would overlap an existing buffer. The size of the buffer zone depends on aquifer characteristics, type of asset (bore or groundwater-dependent ecosystem) and nature or volume of use.

Accounting for environment, existing user rights, water availability and non-licensed interception

Under the South Australian Natural Resources Management Act 2004, existing water users are entitled to an allocation that meets their reasonable requirements, balanced against the capacity of the resource, non-licensed use and environmental needs. Ideally, water allocations should also include only the water that is reasonably available at a site to avoid giving unachievable allocations that may then be sold and the resource potentially extracted. These various considerations have been dealt with by allocating existing surface water users amounts that are less than:

  • reasonable requirements (based on the maximum theoretical requirements for the type, size and location of their enterprise)
  • dam capacity
  • available runoff (average runoff to their dam, taking upstream evaporation and licensed and non-licensed use into account)
  • their share of their management zone's sustainable use limit, where the limit is set on the basis of meeting environmental flow targets, and where all estimated non-licensed use has been subtracted from the limit to determine the volume available for licensed allocation.

As a social and economic consideration, where the volume to be allocated under this system is less than half of the user's reasonable requirements, they are allocated half of their reasonable requirements, capped at the dam capacity.

Allocating water in this way ensures that the most limiting factor is considered (enterprise requirements, water availability or environmental needs), while also providing a safety net to allow existing businesses to continue.

Sharing available water between the ranges and plains

Streamflow from the ranges provides the vast majority of the recharge to the aquifers on the plains. This linkage means that the total volume that can be extracted must be balanced between the two resources.

Under the Natural Resources Management Act 2004 (SA), existing water users are entitled to an allocation that meets their reasonable requirements, balanced against the sustainable capacity of the resource. The total volume of reasonable water requirements exceeds the sustainable limits for both resources. Balancing the total demand between the resources has been achieved firstly by setting allocations for surface water and groundwater independently, based on local resource availability, accounting for non-licensed use, and achieving environmental targets. Secondly, the reduction in total allocations from the total reasonable requirements for each resource were compared and found to be similar. This means that the 'pain' of reductions is shared equally between the resources, and so the allocation limits for these resources were capped at these volumes.

Information requirements to achieve objectives

  • behaviour of water resources in response to rainfall and management (such as rainfall-runoff relationships built into surface water models that reflect the current dam network, models of groundwater level in response to recharge and extraction)
  • environmental water provisions expressed as flow regime measures and targets
  • assessment of management options by local community members, including water users.

Approach taken in dealing with uncertainty

Rainfall and hence streamflow and groundwater recharge are highly variable from year to year. Having allocations that vary from year to year to directly account for this variability was not seen as a viable option for this water allocation plan, because water resource response to climate is not well enough understood; the nature of water capture (dams will intercept an amount of water based on their size and location, not because of the allocation volume assigned to an individual dam); and because it was felt that the community should have an opportunity to come to grips with a licensed water management regime before the added complexity of variable allocations was introduced.

Instead, this uncertainty is dealt with by:

  • modelling surface water scenarios over a period that included wet, dry and average rainfall years
  • modelling groundwater responses to recharge by streamflow under average to dry conditions
  • being conservative in setting allocation volumes and setting an adaptive monitoring framework that includes water resource condition triggers that stimulate investigation and action if required

Approach taken in consulting with stakeholders

The South Australian Murray-Darling Basin Natural Resources Management Board (the Board) and the former South Australian Department for Water , Land and Biodiversity Conservation, now South Australian Department of Environment, Water and Natural Resources, are the major agencies involved in managing water use, and have worked together collaboratively throughout the development of the existing user allocation process and water allocation plan.

A water resources planning committee – made up of community members representing different water resources, areas and enterprises – provided recommendations to the agencies throughout the project, and provided information back to their local communities.

Several rounds of consultation were held throughout the process, which included community meetings with information and discussion sessions, distribution of discussion papers, advertising in local papers and calls for written submissions. These consultation rounds were aimed at a range of stakeholders including water users (including industry groups), environmental groups, local councils, agencies and the broader community.

Compliance actions

The Department of Environment, Water and Natural Resources is responsible for assessing compliance and enforcement for water allocations (via metering of licensed use), licence conditions and water usage.

Monitoring and reporting

The Water Allocation Plan for the Marne Saunders Prescribed Water Resources Area includes a monitoring section that outlines the minimum monitoring and evaluation requirements to assess effectiveness of the water management policies. Required monitoring includes monitoring of water resources (rainfall, streamflow, groundwater pressure or level, salinity in all resources), water usage (through metering and annual reporting by licensed water users) and condition of water-dependent ecosystems (particularly fish, macro-invertebrates, vegetation, geomorphic condition) to assess whether environmental objectives are being met.

More information

More infomation, please visit: National Water Initiative