General features

The Upper Murrumbidgee flows through steep, rocky gorges where undisturbed native vegetation still exists; and broad valley flats where the native vegetation has generally been cleared, and rural and urban activities predominate. Non-riparian vegetation communities in the reach include dry eucalypt and callitris woodlands on valley slopes. In the riparian zone, She-oak woodlands are common on the broader floodplains, whilst bottlebrush and burgan shrublands are generally found on the rockier areas. Riparian Ribbon gum patches persist on river terraces upstream of Point Hut in the ACT. Aquatic and semi-aquatic plants occur in the river channel and in wetlands on floodplains.

Where steep valley slopes occur, shallow soils are common, with numerous rock particles or as pockets of soil within outcropping volcanic rock. Deeper soils with clay-rich lower horizons occur at the foothills of broad slopes in association with deep river terraces close to the river.

Summers are hot and winters cold. Rainfall, at around 600 mm per year, falls throughout the year with higher averages in spring. Drought occurs at regular intervals similar to elsewhere in Australia and combined with possible climate change it is a significant factor in determining the future health of the river.

The river's original natural flow regime was characterised by high winter and spring flows from rainfall in the upper catchment and also snow melt in spring. However, the Tantangara Dam in the upstream of the project area, now diverts 99.6% of the headwater flows which has reduced downstream base flows, flood levels and flood frequency. This means that Lobbs Hole in the midpoint of the reach, receives less than 57% of pre-Tantangara flows (Pendlebury, 1997).

In-stream habitats along the reach include pool-riffle sequences, drought refuge pools, complex benthic (river bottom) substrates, in-stream and overhanging vegetation, and large snags.

The reach supports a diverse range of animal species, although reduction in the health of the river system has contributed to population decline, particularly of aquatic species. The reach includes a range of fish, mammals, birds and reptiles including crayfish, water rats, platypus, water dragons, frogs and turtles.