Water for the environment requirements

Initial investigations have now been completed to specify the water for the environment requirements of the Coorong, Lower Lakes and Murray Mouth region.

This research indicates a flow regime, rather than a fixed volume of water, should be delivered to the region from year to year to secure a healthy, sustainable wetland system.

This regime aims to ensure:

• the River Murray should flow out to sea every year, without the need for dredging
• sufficient water should flow over the barrages to export salt and maintain salinity in Lake Alexandrina below 1000 µS cm-1 electrical conductivity (EC) 95% of the time
• water levels in the lakes should vary seasonally and between years
• higher flows should be delivered as often as was historically the case, to keep the Coorong’s south lagoon healthy.

Doing this will support the described ecological character of the wetland into the future.

A new approach

These investigations are the first attempt to determine the water for the environment requirements for the region by explicitly linking ecological and hydrological (water) requirements.

Past attempts to determine water for the environment targets for the site, although based on the best available knowledge, suggested targets in the form of a single volume or combinations of a few volumes. Also the ecological outcomes were often inferred rather than directly tested or modelled, and the trade-offs were not fully described.

Recent research within the region and tools such as hydrological and ecological response models, mean a more-rigorous approach can now be applied to this important question.

Dr Rebecca Lester of Deakin University (formerly of Flinders University), Professor Peter Fairweather of Flinders University, Dr Kerri Muller of Kerri Muller NRM, and Dr Theresa Heneker and Jason Higham from the department, with assistance from local experts, have worked together to investigate the water for the environment requirements of the region using this new approach.

How the water requirements were determined

Ecological objectives and outcomes were set based on the aim to maintain a healthy, productive and resilient wetland of international importance under the Ramsar Convention.

Flow-related requirements were identified for a wide range of indicator plants, animals, assemblages and processes, each of which were linked to the ecological outcomes.

Salinity thresholds were then determined and modelling identified three-year sequences of barrage flows that would keep salinities below these levels.

Extensive testing across the Coorong, and under predicted climate change conditions, explored the robustness and feasibility of these flow sequences, and the implications of failing to meet them. The potential interaction between barrage flows and an existing proposal to expand the Upper South-East Drainage Scheme was also investigated.

This research has been published in a series of reports.