Lower Lakes, Coorong and Murray Mouth



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4.2 The Living Murray works and water modelling


Modelling completed in 2008 (MDBC 2008) found that the environmental water requirements of the floodplain icon sites (with the exception of Barmah–Millewa and the Lower Lakes, Coorong and Murray Mouth icon sites) could largely be met by a combination of the proposed TLM works, the 500 GL of recovered TLM water and 70 GL long-term Cap equivalent (LTCE) of River Murray Increased Flows.

This modelling was based on a number of assumptions including the use of unregulated flow events for environmental watering actions. It was also agreed as a modelling principle that return flows could be used to water at multiple environmental sites. There are a number of constraints to the implementation of this principle which TLM are currently working to resolve and trialling solutions.

Further modelling is also planned to allow greater optimisation of works and measures to achieve icon site ecological objectives as a greater understanding of operating scenarios is gained.

4.3 Operating regimes for environmental watering actions


This section of the Environmental Water Management Plan provides a broad description of the proposed operating regimes to maximise ecological outcomes from the use of The Living Murray water portfolio and works. To meet the proposed operating regimes, a combination of unregulated and regulated environmental water may be used.

While this environmental water management plan focuses on the use of environmental water from The Living Murray water portfolio, there will also be other sources of environmental water available to meet the proposed regimes, including the Commonwealth Environmental Water Holder, state allocations and private donations. The contribution of varying operating regimes to the achievement of the ecological objectives is detailed further in Table .


Table : Operating regimes contribution to the ecological objectives

Ecological watering objective

Icon site First Step Decision objective

Vegetation community *

Works or other mechanisms to assist meeting objectives


Preferred level (Lakes Alexandrina and Albert, m AHD)

Long term average frequency


Duration

(days)

Water availability scenario

Estimated volume of water required

(GL)

Preferred operating scenario

Improve the health and resilience of aquatic ecosystems

  • Fringing wetlands

  • Coorong and Lakes riparian habitat

  • Coorong north and south lagoon

  • Murray Mouth

  • Barrage operation/manipulation to lower and raise Lake levels

  • Barrage fishways operational year-round

  • Large flows through all barrages

  • Each barrage has most bays open

  • Flows directed to keep Murray Mouth open, restore large extent of estuarine habitats in the Coorong and reduce salinities in the South Lagoon

Lake levels vary seasonally between 0.35 - 0.75m AHD

Annually

365

Dry - Median

SA Entitlement (1,850 GL/yr) + ADF presumed

>1,800 ML/day out barrages (>650 GL/yr)



Lake levels vary seasonally between 0.5 - 0.83m AHD

Every third year

365

Median - Wet

SA Entitlement + ADF + large unregulated flows presumed

>2,800 ML/day through barrages (>1,000 GL/yr)



Ecological health of priority habitats and wetlands have been protected or improved

  • An open Murray Mouth

  • More frequent estuarine fish recruitment

  • Enhanced migratory wader bird habitat

  • Fringing lakes wetlands

  • Coorong and Lakes riparian habitat

  • Coorong north and south lagoon

  • Murray Mouth

  • Barrage operation/manipulation to lower and raise Lake levels

  • Barrage fishways operational year-round

  • Medium attractant flows from Goolwa and Tauwitchere barrages

  • Release from Boundary Creek for estuarine conditions

  • Each barrage has some bays open

  • Larger volumes to the Lakes allow for fluctuating levels

  • Maintain water levels and salinity in Coorong to promote Ruppia

  • Maintain estuarine habitats to facilitate fish recruitment

Lake levels vary seasonally between 0.35 - 0.7m AHD

Annually

365

Median

SA Entitlement + ADF + unregulated flows

>1,800 ML/day out barrages (>650 GL/yr)



Lake levels vary seasonally between 0.5 - 0.83m AHD

Every third year

365

Median

SA Entitlement + ADF + unregulated flows

>1,800 ML/day out barrages (>650 GL/yr)



Minimum operating scenario

Ensure priority habitats and wetlands have maintained their basic functions

  • Coorong and Lakes riparian habitat

  • Fringing lakes wetlands

  • Coorong North lagoon




  • Barrage operation / manipulation to lower and raise Lake levels

  • Allow larger volumes to Lakes to maintain water levels and prime site for recovery

  • Barrage fishways operational for minimum 6 months

  • Small attractant flows from Goolwa and Tauwitchere barrages next to fishways in Spring

  • Small release from Boundary Creek for estuarine conditions

  • Murray Mouth dredging

Lake levels vary seasonally between 0.35 - 0.7m AHD

Annually

365

Dry

SA Entitlement (1850 GL/yr)

~1,800 ML/day out barrages (~650 GL)




Lake levels vary seasonally between 0.5 - 0.83m AHD

Every third year

365

Dry

SA Entitlement (1850 GL/yr)

~ 1,800 ML/day out barrages (~650 GL)




Avoid irretrievable loss of key environmental assets

  • An open Murray Mouth

  • More frequent estuarine fish recruitment

  • Enhanced migratory wader bird habitat

  • Critical habitats

  • Priority fringing wetlands

  • Operate Lock 1 and barrages to maintain lakes >0 m AHD (acidification threshold)

  • Pumping to threatened fish refuges

  • Pumping to fringing lakes wetlands

  • Barrage fishways operational for minimum 2 months per year, alternatively use Goolwa boat lock if negative head

  • Divert water from SE drainage system into Coorong

  • Murray Mouth dredging

Maintain lake levels above 0 m AHD

Emergency actions implemented for duration of extreme dry period

365

Extreme dry

9 GL of water through the fishways over 2 months (or use boat lock if water levels too low);

Required volume to maintain lakes >0 m AHD depends on starting level (refer Table 16 for corresponding volumes for 10cm increments)




*-Area of inundation in the Coorong and Murray Mouth Estuary fluctuates with tidal variation; Lower Lakes fringing habitat fluctuates with water level


4.3.1 Water delivery and existing water delivery infrastructure


The LLCMM icon site receives most of its water through gravity-fed flows from the River Murray through Lock 1, 275 km from the Murray Mouth. Under previous operating conditions, the Lower Lakes were maintained at an average pool level of around 0.75 m AHD to Lock 1 at Blanchetown, to ensure sufficient water for irrigation activities. Pool level fluctuated over the season around this level, and was highest in early summer and lowest in winter. This pool level is achievable when South Australia receives Entitlement (1,850 GL/year) or above-Entitlement Flow. Entitlement or above-Entitlement Flow would typically be achieved annually, outside of extreme drought conditions. During Entitlement Flow conditions, approximately 100 GL is available to release through the barrages.

Barrages


Barrage releases are a key management tool for keeping the Murray Mouth open and to control the water level in the Lower Lakes. Goolwa, Mundoo, Boundary Creek, Ewe Island and Tauwitchere barrages Table were built between 1935 and 1940, in order to separate the fresh water of the Lower Lakes from the estuarine-marine conditions of the Murray Mouth. They are operated by SA Water on behalf of the MDBA.

Table : Barrage details



Description

Length

Bays

Combined bay length

Gates

Goolwa

632 m

128

632 m

123 stop log bays

Mundoo

792 m

26

117 m

26 stop log bays

Boundary Creek

244 m

6

26 m

6 stop log bays

Ewe Island

2,270 m

111

470 m

50 stop log bays, 61 radial gates

Tauwitchere

3,658 m

322

1,368 m

130 stop log bays, 192 radial gates

Fishways


Associated with the operation of the barrages are a series of fishways (Table ). These structures are located at Goolwa and Tauwitchere barrages, and allow fish to travel bi-directionally between Lake Alexandrina and the Murray Mouth estuary. Reduced flow velocities and turbulence allow fish of various sizes to successfully navigate through these structures.
Table : Barrage fishway details

Description

Volume/day (ML)*

Year installed

Funded by

Goolwa large vertical slot fishway

57

2004

MDBA

Hunters Creek vertical slot fishway

7

2008

MDBA

Tauwitchere large vertical slot fishway

35

2004

MDBA

Tauwitchere small vertical slot fishway

4

2009

MDBA

Tauwitchere rock ramp

50

2004

MDBA

*Note: approximate volumes are estimated as at Full Lakes Supply Level (0.75-0.8 m AHD), with releases likely to change dramatically in response to high tides or strong wind events.

Managed fringing wetlands


Within the Lower River Murray, many wetlands which were previously ephemeral are now permanently inundated, due to river regulation (Pressey 1986). Flow control structures to re-create a more natural wetting and drying regime, or to hold water on the floodplain have been installed at several sites which have had an ecological baseline survey monitoring program undertaken and a wetland management plan developed (DWLBC 2003). While management of the Lower Lakes water level is key to wetting and drying the fringing wetlands, several wetlands can be hydrologically managed using existing flow-control structures (Table ). These wetlands are important during times of high lake and Coorong water levels, as water levels can be lowered to provide mudflat habitat for waders.

Table : Description of managed fringing wetlands of Lakes Alexandrina and Albert



Description

Type

Year Installed

Funded By

Narrung wetland

Stop logs and rotating carp screens at ferry road and inlet channel connections

2007 & 2009

SA MDB NRM Board / CTLAP

Waltowa wetland

Sluice gate at inlet under Princes Highway on lake side

1999

NHT

Tolderol wetland

Sluice gates and pump from inlet channel

2001

NHT

Hunters Creek

Vertical slot fishway with stop logs and attractant flow at Hunters Creek estuary

2008

EWMP (MDBA)

Lower Lakes pipeline


Reduced freshwater flows to the Lower Lakes during the recent drought resulted in salinity levels within the lakes rising well above (as much as five times) that which was once suitable for stock, domestic supplies and irrigation. In order to provide reliable, quality drinking water to the communities reliant on the lakes, as well as reduce the pressure of water extraction on the lakes, 170 km of pipeline was installed to deliver quality drinking water to households and properties at Langhorne Creek, the Raukkan Aboriginal Community and the Narrung and Poltalloch Peninsulas. A separate irrigation pipeline delivering irrigation water to the Langhorne Creek and Currency Creek communities was also installed in 2010, in time for the 2009–10 irrigation season. Another pipeline to supply Point Sturt with drinking water was connected to the existing Milang–Clayton system, with an additional pipeline to supply Hindmarsh Island with drinking water connected to an existing system which receives water via the Myponga Reservoir. While not directly related to the delivery of environmental water to the icon site, the pipeline does allow for a more variable lake operating regime to be implemented in the future, pending suitable consultation with all water users. This project was implemented by the South Australian Murray Futures CLLMM program, funded by the Australian Government’s Water for the Future program.

Telemetered surface water monitoring stations


Eleven locations for new surface water quality logging equipment were determined in 2006–07 through the LLCMM icon site program. Sites were chosen to coincide with existing ecological monitoring sites used by the CSIRO Water for a Healthy Country: CLLMM Ecology project, and in areas where no other logging was available, in order to assist with research and consistent data collection. The extension of the system into the Coorong allows for the hydrological and physical effects of barrage operation decisions to be viewed as they happen in the estuarine environment. The enhanced Surface Water Monitoring System therefore demonstrates to the operators of the barrages with greater accuracy how the hydrology, physical conditions and ultimately the estuarine ecosystem response to management actions. This allows for management decisions to be more accurately made around barrage operations and environmental water delivery. This project was implemented by the then South Australian Department for Water, funded by the MDBA. A number of telemetered surface water monitoring stations in the LLCMM were decommissioned during 2011 due to reduced funding.

The surface water monitoring system can be viewed on-line:



http://data.rivermurray.sa.gov.au/

4.3.2 Proposed environmental water delivery works

South East flows to the Coorong South Lagoon - implementation


As well as barrage releases, water and salinity levels within the Coorong are influenced by redirected groundwater and surplus surface water from the upper south east, which is released into the South Lagoon of the Coorong at Salt Creek. The Coorong South Lagoon Flows Restoration project was developed through The Living Murray EWMP program, and progressed through modelling and investigations to determine potential water delivery and salinity benefits to the Coorong South Lagoon through the further redirection of drainage water. At the time of developing this environmental water management plan, a funding proposal was with the Department of Sustainability, Environment, Water, Population and Communities for approval under the South Australian Murray Futures program funded through the Australian Government’s Water for the Future program.

South Lagoon pumping


A proposal to pump hyper-saline water out of the South Lagoon of the Coorong for ecological benefit is being considered. Initial assessments have shown that this project is feasible. If implemented, the project would involve minor highway upgrades, a pumping station - on the western side of the lagoon to reduce visual impacts, a pipeline from the South Lagoon to the Southern Ocean, monitoring of salinity levels in the Coorong and the sea and regular meetings with local stakeholders. At the time of developing this environmental water management plan, a funding proposal was with the Department of Sustainability, Environment, Water, Population and Communities for approval under the South Australian Murray Futures program funded through the Water for the Future program. The future of this project is dependent on future South Lagoon salinities and the ability to export salt from the Coorong under current flow conditions using existing barrage infrastructure.

Additional barrage fishways


By building on the existing knowledge gained through the Murray Fishways Program and the MDBA funded Barrage Fishway Monitoring program, additional fishways may be installed at priority locations on the barrages. This will improve connectivity between the estuarine and freshwater environments, and provide passage for a greater range and number of fish and in a greater number of locations. At the time of developing this environmental water management plan, a funding proposal was with the Department of Sustainability, Environment, Water, Population and Communities for approval under the South Australian Murray Futures program funded through the Water for the Future program.

Automated barrage gates


Automated barrage gates provide the opportunity for barrage operators to remotely operate the opening and closing of barrage bays. This may allow for some releases into the estuary to be made under low lake level conditions, but still prevent salt-water ingress into Lake Alexandrina. While already installed at Mundoo, Ewe Island and Tauwitchere, further modifications are required. Boundary Creek may also benefit from the installation of automated gates.

Channel maintenance for Lower Lakes fringing wetlands


Many freshwater channels associated with the Lower Lakes are ‘choking’ from sand drifts or sediment accumulation which may lead to dense build-up of Typha spp. and/or Phragmites spp., which further exacerbates the problem. Removal of channel blockages is required to maintain connectivity and may be best achieved using an excavator. Sand build up across channel mouths may be prevented by planting ‘buffer zones’ of native reeds, sedges or rushes (e.g. river club rush, (Schoenoplectus validus)) to buffer wave action which may lead to sand build-up.

Fringing lakes wetland hydrological management


While some fringing lakes wetlands have flow control structures that allow for hydrological manipulation (see Section 4.3.1 Water delivery and existing water delivery infrastructure, additional wetlands where a baseline survey has been undertaken (SKM 2004; SKM 2006) could also be managed in a similar fashion for enhanced ecological outcomes following completion of a management plan. This is especially critical during ‘wet’ water years, when mudflat habitat is flooded in both the lakes and Coorong due to high water levels. Managed lakes wetlands are then the only areas in the icon site where water levels can be lowered to create suitable mudflat habitat for waders. Upgrades to existing flow control infrastructure at existing managed wetlands could also improve hydrologic management. A number of new culvert designs have already been developed (Tolderol, Hindmarsh Island and Loveday Bay) through The Living Murray Environmental Works and Measures Program.
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