Lower Lakes, Coorong and Murray Mouth



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4.4 Water accounting and measurement


Water accounting methodology will be developed and agreed in advance by TLMC and the Basin Officials Committee (BOC). Consistency of water accounting methodology will be sought wherever possible. Where relevant, water accounting will be consistent with the Water Accounting Conceptual Framework and Australian Water Accounting Standards. The best available, most appropriate and cost-effective measurement technique will be used to determine environmental water use. The appropriateness of the measurement technique is likely to differ from icon site and event. For example, under dry conditions environmental water pumped into Hattah is likely to be measured via a meter and return flows measured via a gauging station. Under wet conditions, environmental water returning from Barmah–Millewa Forest and other upstream sites will need to be modelled. It should be noted that current calculations for barrage releases are estimates only, and a better calculation of discharge volumes is needed in the near future taking into account lake and estuary water level and bay openings.

4.5 Evaluation and management of potential risks


A number of risks have been identified associated with the Lower Lakes, Coorong and Murray Mouth Icon Site EWMP (Table ), adapted from DSEWPAC (2011). Monitoring and mitigation will be carried out where possible. The results will be taken into consideration when implementing adaptive management principles. These risks and mitigating measures are further detailed in a Risk Monitoring Plan. The risks identified have been linked to LLCMM icon site First Step Decision objectives where relevant.

Risks associated specifically with climate change including sea level rise and reduced inflows have been further explored in Matthews (2005) and Lester et al. (2009b).


Table : Potential risks and mitigation strategies in relation to Lower Lakes, Coorong and Murray Mouth icon site objectives

Threat

Raw risk strategy

Mitigation strategy

Mitigated risk strategy

FSD impacted

Likelihood

Consequences

Risk ranking

Likelihood

Consequences

Risk ranking




Acid sulphate soils

Possible

High

Severe

Implement Real Time Management Strategy (RTMS)

Possible

Critical

Severe

F B

Areas of unstable bank around Lake Alexandrina and Albert and main river channel could be destabilised by elevating or lowering water levels

Possible

Minor

Low

Monitor areas and if necessary implement bank protection measures before undertaking subsequent lake level fluctuation. Adjust rates of rise and fall as necessary

Unlikely

Insignificant

Low

F B

Benefits to alien species

Possible

Moderate

Medium

Monitor and apply an adaptive management approach to pest animal and plant control

Possible

Minor

Low

F B

Adverse community reaction to releases of water

Likely

Moderate

Medium

Liaise with SAMDBNRMB and LLCMM community advisory panel. Make pre-emptive media releases

Possible

Minor

Low

-

Blackwater

Possible

Moderate

Medium

Pre-emptive media releases, implement large barrage releases (water permitting) to flush out blackwater

Unlikely

Minor

Low

F

Water loss – water exits Murray Mouth without mixing with waters of the North Lagoon

Possible

Moderate

Medium

Monitor and apply an adaptive management approach. Adjust flow releases between barrages to enhance mixing

Unlikely

Minor

low

F B

Harmful increase in sediment transport causing unwanted movement in the Murray Mouth

Unlikely

Minor

Low

Considered unlikely at flow rates proposed. Adjust flow releases between barrages to avoid the extent of unwanted results

Unlikely

Insignificant

Low

F B M

Not achieving the proposed ecological objectives of the EWMP’

Possible

Critical

Severe

Maintain existing regime of lobbying and sourcing water to achieve outcomes. Continue monitoring and research programs to determine the achievement of outcomes.

Possible

Critical

Severe

F B M

Climate change- rising sea level, reduced rainfall in the Basin

Almost certain

Critical

Severe

Continue to assess risk to ecological assets. Assess engineering solutions to maintain site’s ecological character

Almost certain

Major

Severe

F B M

Water required for icon site is not available (e.g. extreme drought) leading to loss of key environmental assets, site desiccation, possible species loss, closure of Murray Mouth

Possible

Critical

Severe

Develop and implement water bids for small volumes for protection of refugia and maintenance of lakes water levels , dredge Murray Mouth, ‘rescue’ threatened species, implement RTMS

Possible

Moderate

Medium

F B M

FSD Objectives: M refers to open Murray Mouth, B refers to enhanced migratory bird habitat and F refers to more frequent estuarine fish recruitment.



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