River regulation and water use for consumptive purposes have significantly altered the flow regime of rivers across much of the Murray-Darling Basin.
Flows over river banks are beneficial for the environment because they connect habitats along the floodplain with each other and with the main river channel. Such connections enable species to access refuge habitat areas, to find mates to breed with or to recolonise suitable habitats – all of which are important for their long-term survival. In addition, flooding increases food resources for species downstream of the flood location.
Flood volumes have been greatly reduced, such that the average annual flood volume is now less than half of the volume prior to development. Similarly, the length of time between flood events during dry times has grown substantially to now be more than twice that experienced prior to regulation and diversion of river flow.
In 2013 the Constraints Management Strategy was produced by the Murray-Darling Basin Authority to identify and describe the physical, operational and management constraints that are affecting environmental water delivery for seven key areas across the Basin, including the River Murray in South Australia.
While the main goal of relaxing constraints is to provide greater scope for environmental watering for the floodplain and end of system, relaxing constraints also provides greater capacity to manage water for consumptive users and improve access for communities and landholders during natural high flow events.
Benefits to South Australia
South Australia will benefit from having coordinated flows of up to 80,000 megalitres per day at the border for a month, up to three times a decade. This flow is below the level of 95,000 megalitres per day that occurred in 2016 and well below the 1956 flood level of 341,000 megalitres per day.
As a result of the 1956 flood and subsequent planning controls, major towns and infrastructure in South Australia are generally not located on floodplains. However, inundation of some riverfront land, jetties, banks, marinas, pontoons and public roads will occur during high flows and ways to mitigate the effects are being identified. Providing more culverts and upgrading roads, banks, walls, boating and marina infrastructure, will also improve access for communities and landholders during natural high flow events.
What is happening?
Since the release of the Constraints Management Strategy, Basin governments have undertaken pre-feasibility studies and produced business cases outlining the works and costs that will ease system constraints. This has included exploring measures that would facilitate environmental flows, improve infrastructure, erosion control works and easement negotiation. Addressing these constraints will provide additional benefits for landowners during periods of natural high flows.
You can read the business case for South Australia’s constraints measure.
This project is part of the package of projects for the Sustainable Diversion Limit (SDL) Adjustment Mechanism and now that the changes to the SDLs have been incorporated into the Basin Plan, the next phase of work begins.
Community engagement in the implementation of this work to relax constraints will be fundamental to its successful delivery. Over the next two years, the department will undertake further planning, designs and engagement with the community to work out the detailed scope and costs and commence implementation.