The South Australian River Murray is a highly regulated system comprised of a series of

The South Australian River Murray is a highly regulated system comprised of a series of lake-like pools with largely stable water levels. These relatively deep, slow moving pools of water with stable water levels have impacted the ecological condition of the river system. Channel and floodplain habitatsare influenced by the river geomorphology and water quality,which are in turn influenced by water depth, water velocity, flow variability and flow seasonality. In particular, flow variability influences hydraulic and physical habitats that sustain populations and communities of aquatic flora and fauna. 3

Modelled median monthly flowvolumes (GL) on the Murray River at Albury under natural and 1988 development conditions, indicating the reversal of the natural seasonal flow pattern due to irrigation storage and delivery Modelled median monthly flowvolumes (GL) at downstream of Yarrawonga Weir on the Murray River under natural and 1988 development conditions, indicating the reductions in flow volumes due to irrigation diversions Modelled median monthly flowvolumes (GL) at Euston on the Murray River under natural and 1988 development conditions, indicating the reductions in flow volumes but a return to a near-natural season pattern downstream of all irrigation diversions Young, W.J (ed.), 2001, Rivers as Ecological Systems: The Murray-Darling Basin, Murray Darling Basin Commission, Canberra 4

Alpine Systems Ephemeral Rivers Forests Large Rivers Wetlands Lakes The Murray Mouth The desired long-term ecological character for the Coorong, Lower Lakes and Murray Mouth (CLLMM) region is currently set at the ecological conditions in 1985 when this region was listed as a Wetland of International Importance under the Ramsar Convention. RAMSAR sets simple but general targets of: (1) maintaining the Lower Lakes as a freshwater lake system, (2) maintaining the Coorong with a gradation of estuarine ecosystems in the north to moderately hypersalineecosystems in the south; (3) an open Murray Mouth. 5

Tourism Agriculture Environmental Drinking Water Supply 6

This figure shows the change in the median annual flow from natural to current conditions (as at 2002) at points along the River Murray. At Albury the river carries greater than natural flows as a result of extra water diverted from the Snowy scheme. Downstream of major diversions (eg. Yarrawonga Weir), the flow in the river is less than it was naturally. Also, some tributaries now deliver less water to the Murray than they would have under natural conditions (ie. without river regulation). The median annual flow to the sea is currently about 27% of what it was under natural conditions. Source: Gippel, C.J. and Blackham, D. 2002. Review of environmental impacts of flow regulation and other water resource developments in the River Murray and Lower Darling River system. Final Report by Fluvial Systems Pty Ltd, Stockton, to Murray- Darling Basin Commission, Canberra, ACT. Link to report: http://thelivingmurray2.mdbc.gov.au/ data/page/1480/final_review_reg_impacts_efl ow1.pdf 9

In the Murray River the biomass and production rate of phytoplankton (algae) increases substantially as flow velocity declines (e.g. below 0.2 m s-1). As flow rates reduce there is also a greater chance of thermal stratification occurring, especially during summer. Warm, transparent water in the upper layers promotesthe growth of algae. These low velocities are uncommon in the river channel, however, in SA this can occur in stagnant areas and in the weir pools behindlocks. This is especially the case when river discharge falls below about 3000 ML/day. 13

Ref: Young, W.J (ed.), 2001, Rivers as Ecological Systems: The Murray-Darling Basin, Murray Darling Basin Commission, Canberra Flooding is the single most important natural influence on floodplain vegetation. Low level floods (<40,000 ML/day) are required to connect the wetlands and intermittent streams adjacent to the river channel and maintain a connection forthe river channel biota to reach these large productive areas suitable for feeding and sometimes reproduction. Moderate floods (40,000-80,000 ML/day) connect higher reaches of the floodplain to the channel and are important in transferring nutrients, organic matter and other materials between the river and the floodplain. Small changes in floodlevels can have a large effect on the area of flooded habitat. 18

Source: Australian Dryland Salinity Assessment 2000 (National Land and Water Resources Audit 2000) and NSW Office of Environment and Heritage Vegetated 1Perennial, deep-rooted native vegetation uses most of the available water and prevents leakage to the groundwater system. 2 Evapotranspiration rates are high. 3 Surface run-off and erosion rates are low. 4The water table remains well below the surface and a range of productive agricultural land uses are carried out. Cleared vegetation 1Replacing native vegetation with annual crops and pastures that have shorter growth cycles and shallow root systems reduces water uptake and increases leakage to the groundwater system. 2Evapotranspirationrates are lower. 3Surface run-off and soil erosion rates increase. 4The water table rises (also aggravatedby excessive irrigation and high weir pool levels), bringing salts stored deep in the soil to the surface (capillary rise) where they affect plant growth (production) and water quality The high groundwater salinities in this region mean that the floodplain soils naturally contain high amounts of salt. This, combined with the semi-arid climate with very irregular flooding, meant that salt accumulated in the dry period between floods but was leached whenever inundation occurred, thus creating a dynamic equilibrium that was stable in the long-term. River regulation has reduced the frequency and duration of the floods that leach salt from the plant root zone. The combined effect of these processes (i.e. clearing, irrigationand reduced flooding) is long-term salt accumulation in the floodplain soils. 21

Ref: Murray-Darling Basin Authority 2011, The proposed environmentally sustainable level of take for surface water of the Murray-Darling Basin: Methods and outcomes, MDBA publication no: 226/11, Murray-Darling Basin Authority, Canberra. 23

Riverland - Chowilla Floodplain (measured as Flow to South Australia) Ref: Murray-Darling Basin Authority 2011, The proposed environmentally sustainable level of take for surface water of the Murray-Darling Basin: Methods and outcomes, MDBA publication no: 226/11, Murray-Darling Basin Authority, Canberra. 25

In-Channel Flows - Lower River Murray (measured as Flow to South Australia) Ref: Murray-Darling Basin Authority 2011, The proposed environmentally sustainable level of take for surface water of the Murray-Darling Basin: Methods and outcomes, MDBA publication no: 226/11, Murray-Darling Basin Authority, Canberra. 26