The Environmental Enhancement of the Lower Lakes, Coorong and Murray Mouth Project commenced in 2005 and comprises a conglomeration of various smaller projects in the region such as fishways, water quality monitoring stations and various on-ground works.
Fishways for barrages
As part of the Murray–Darling Basin Authority’s ‘Native Fish Strategy’ (MDBC 2006b), a program was undertaken to install fishways on the main channel weirs and barrages of the River Murray in order to re-instate connectivity from Lake Hume to the sea (Barrett & Mallen-Cooper 2006).
Tauwitchere Barrage is one of five barrages which separates the Lower Lakes from the Coorong and Murray Mouth and as part of the program was fitted with both a large vertical slot fishway in the centre of the barrage and a rock ramp (Figure ) and small vertical slot fishway at the Pelican Point end of the barrage. A regulator and fishway was also installed in Hunters Creek on Hindmarsh Island to enable water efficient operation to deliver low volumes of water to the Coorong during periods of minimum flow for the best ecological outcomes, while preventing the stranding of resident freshwater fish in the Coorong or impeding the migration of diadromous fish species. The fishways were fitted between 2004 and 2009.
Figure : Vertical slot fishway at Tauwitchere Barrage
In August 2006 a project was initiated by SARDI Aquatic Sciences to investigate the movement and recruitment ecology of freshwater and estuarine fishes in the Coorong and Lower Lakes utilising three existing barrage fishways (Goolwa vertical-slot, Tauwitchere vertical-slot and rock-ramp) as a way to assess the effectiveness of the current infrastructure for native fish passage (Figure ) and to provide supporting information for the design and construction of new fishways.
Before these particular fish investigations there was very little information to describe the requirements of fish communities in the Coorong and Lower Lakes and in particular fish species that move between the two environments. Furthermore there was little data on the link between freshwater inflows and the spawning and recruitment of fish species in the Coorong.
The first stage of the monitoring (September 2006 – March 2007) produced substantial preliminary data on fish movement and response to freshwater flows into the Coorong. Based on this data, the report recommended that in times of limited water availability, fishway operation between August and January (as a minimum) should be viewed as a management priority.
Fishways were closed in March 2007 as drought continued within the Murray–Darling Basin and water levels in the Lower Lakes decreased. Sites below Tauwitchere Barrage sampled in 2006–07 were again sampled in 2007–08. However, with the fishways shutdown and zero flows into the Coorong, objectives in 2007–08 were broadened to document the response of fish to unprecedented (since river regulation) drought conditions.
Figure : Barrage fishway monitoring being undertaken by SARDI Aquatic Sciences
The cessation of freshwater discharge and fishway operations in 2007–08 significantly reduced the abundance and diversity of freshwater and estuarine dependant species in the Coorong downstream of Tauwitchere Barrage. Of note was the decline in abundance of diadromous fishes, and increases in the abundance of marine opportunists. Elevated salinities exposed an estuarine adapted ecosystem to predominantly marine conditions and an increasingly hypersaline environment.
In 2008–09 the barrages again remained closed in response to the negative headloss across the barrages and concerns of declining water quality in the Lower Lakes. Despite these closures, Tauwitchere and Goolwa barrages were sampled to describe the fish assemblages below each barrier. Sites remained consistent (between 07–08 and 08–09) at Tauwitchere Barrage, whilst additional sites were selected for sampling at Goolwa Barrage to allow comparative analysis of the species assemblages between barrages.
Abundances of freshwater and diadromous species at Tauwitchere and Goolwa barrages were very low compared to the previous two sampling seasons. At the same time, the proportion of marine species increased and in the continued absence of freshwater inflows the estuary resembled a marine dominated tidal system. The significant decline in the abundance of diadromous fishes and most importantly continued evidence of poor recruitment of these species was cause for concern for the long-term viability of these populations in the Lower Lakes and Coorong.
This project has generated extensive data on the ecology of fish assemblages at the freshwater/estuarine (and now marine) interface of the Coorong and Lower Lakes. A paper was produced discussing the changes in fish assemblages and recruitment of diadromous fish over the three year sampling period (Zampatti et al. 2009). Data has also been used to continuously inform not only barrage operation and drought response but also the location and design of future fishways, condition monitoring of the icon site and the development of future monitoring methodologies. Data collected as part of this project also contributed to the assessment of several interim ecological targets within the Lower Lakes, Coorong and Murray Mouth Environmental Management Plan (MDBC 2006a).
Data collected as part of this project has contributed to the development of the Goolwa Barrage Fishway environmental water bid.
Telemetered surface water monitoring stations
This project extended the range of the telemetered surface water monitoring systems into the estuarine reaches of the North Lagoon of the Coorong.
Eleven locations for the logging equipment were determined as part of the adaptive management program of DWLBC, from Goolwa Barrage to the South Lagoon. In addition, sites were chosen to coincide with existing ecological monitoring sites used by the CSIRO Water for a Healthy Country: CLLAMMEcology project, 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 decisions to be viewed as they happen in the estuarine environment. For example, following the opening of structures at Boundary Creek the system will allow the monitoring of the water levels and relative salinity as they change in the channel downstream into the Coorong.
Localised conditions have a direct effect on biota. If the system is not brackish, containing a mix of fresher water, marine species will begin to dominate; if the system is freshened too much species stimulated into reproduction can be adversely affected.
The enhanced Surface Water Monitoring System therefore demonstrates to the operators of the barrages with some precision how the hydrology, physical conditions and ultimately the estuarine ecosystem respond to management actions.
The current extent of the surface water monitoring system can be viewed on-line:-
This website illustrates live lake levels, salinity readings and wind direction at various sampling points around the Lower Lakes and Coorong. Currently it is routinely used to assist with decisions on barrage operations. It readily displays the hydrological effects of wind upon Lake levels and remote awareness of seiche has many advantages for barrage decision-making.
Additional on-ground works
This project involved a prioritisation process where 15 sites identified within the LLCMM were ranked based on predicted improvements in ecological condition for 12 ecological values. A number of sites were also identified for which the proposed works would contribute significantly to ecological values of the entire CLLMM region.
Hindmarsh Island, Dunn’s Lagoon, Tolderol and Milang ranked very highly and this lead to the development of management and operational plans. Within each plan recommendations were made for on-ground works which would contribute to improving the overall health of the wetland. The following recommendations have been implemented with these high priority wetlands:
• A stormwater capture and release system was installed in Milang Wetland in order to increase the amount of stormwater run-off the wetland receives. This will promote habitat for the threatened migratory species Latham’s Snipe (Gallinago hardwickii). As well as providing a source of water to the wetland while it is disconnected from Lake Alexandrina, the storm water run-off which is serviced by a gross pollutant trap will increase the area of wetland which receives water.
• The Dunn’s Lagoon management plan identified the need to preserve the seed bank of aquatic vegetation communities during the drought. In order to achieve this, blocking banks would need to be constructed across the lagoon inlets. Before carrying out large-scale works seed bank trails were set up to determine if there would be a positive response from the soil seed bank if artificial inundation through pumping were to be implemented.
The trials were conducted by SARDI Aquatic Sciences (Figure ). Soil samples were collected and submerged in fresh (control), 6,400 (Lake Alexandrina) and 11,000 (Goolwa Channel) EC water. Conductivity and depth measurements were undertaken at least twice a week and germination counts every fortnight.
Based on the results of the seed bank trials, the recommendation of installing blocking banks across the inlet of Dunn’s Lagoon in order to artificially inundate the wetland via pumping was withdrawn. Current lake levels have risen and the wetland has reconnected with Lake Alexandrina, resulting in natural inundation of the wetland.
Figure : Seed bank trials comparing sediment from Dunn’s Lagoon and Shadows Lagoon
• Works on Hindmarsh Island were recommended in order to provide estuarine conditions and fish connectivity. This was achieved though the upgrade of a structure to facilitate greater connectivity. Once complete the structure will incorporate stop logs and a fish grate.
• Priority on-ground works identified in the Tolderol management plan include the upgrade of pipe culverts, the dredging of the main water access channel, an upgrade of regulating structures (i.e. stop logs and sluice gates). Designs have been developed for a structure and the channel has been cleared to allow for reconnection with Lake Alexandrina.
• Designs have also been developed for a culvert which will allow Loveday Bay Wetland to be reconnected with Lake Alexandrina. A causeway, built across the inlet channel prevents water flowing through from the lake and the pipes currently under the causeway are too high to allow a connection at pool level. The structure designs propose a seven opening box culvert with stop logs on the lake side to allow management of the wetland.