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Legislative Assembly for the ACT: 1998 Week 1 Hansard (29 April) . . Page.. 131 ..

MS TUCKER (continuing):

in the Murrumbidgee. As we all know, the Murrumbidgee River is very important to Canberrans. As the Murrumbidgee River Corridor management plan states, it has recreational, scenic, cultural and ecological values. As that report also states, the Murrumbidgee River is degraded along its length. Much of the cause of degradation is river regulation. Currently, only one per cent of the flow is released into the Murrumbidgee from the Tantangara Dam. The dam became operational as part of the Snowy Mountains scheme in 1960. It captures the headwaters of the Murrumbidgee River and also water from the Upper Goodradigbee River and a number of small tributaries. The dam diverts virtually all of the flow in the Murrumbidgee River at this point to the Eucumbene Dam in the Snowy River catchment, which is then diverted to either the Tumut or Geehi river system.

An expert panel environmental flow assessment of the Upper Murrumbidgee River prepared by the New South Wales Environment Protection Authority in late 1997 made a number of recommendations about minimum flow requirements downstream of Tantangara Dam. These recommendations include detail of flow requirements which would facilitate repair of the river environment. For example, of interest is the recommendation that the natural seasonal variability of flow must be mimicked. This is because in many instances such variation is important to biological and ecosystem processes. Increased seasonal variability would allow and encourage fish passage and spawning. The area and diversity of habitat for fish and macroinvertebrates would be increased. Higher seasonal flows would minimise the accumulation of silt and fine organic sediment, providing improved habitat for macroinvertebrates and cleaner gravel beds for fish spawning activities. The invasion of the channel by exotic and other vegetation also would be minimised.

Also of special interest to members here would be the recommendation that a minimum flow be maintained at Halls Crossing, or natural flow at this point, whichever is the lesser. Achievement of this minimum flow may require environmental flow releases from the ACT water supply storages and/or urban lakes. This is because such minimum flow during summer months would improve water quality and minimise the cumulative stress placed on aquatic and riparian ecosystems from apparent increased nutrient levels and reduced flows downstream of the ACT. I will read for members a section from the conclusions of this report:

The extent of flow regulation in the catchment has impacts on the geomorphology, vegetation, aquatic habitat and ecology of the upper Murrumbidgee River. The impacts are greatest in the reach immediately below Tantangara Dam, and include reduced habitat variability and refuge habitat, reduced diversity of macroinvertebrate fauna -

this was written by scientists -

colonisation of the constantly shallow areas of the channel by water lilies, and invasion of the streambed by exotic and native vegetation. The loss of flushing flows since the construction of Tantangara Dam has contributed to sedimentation and the accumulation of a considerable

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