Indicator: Streambank disturbance

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What the results tell us for Tumut

See also:
| Riparian vegetation | Streambank rehabilitation | Livestock access to streams |

Catchments within Tumut Shire were not assessed and designated stress ratings in the Stressed Rivers Assessment Reports (DLWC, 1999). However, the report has indicated that the condition of stream banks and beds is highly variable within and across catchments (Table 1). The streams of the Gilmore/Sandy, Goobarragandra, Goodradigbee and Tantangara catchments were in the best condition and the streams of the Tarcutta catchment were in the poorest condition (Table 1). Primary stress factors included plantation forests and roading (Gilmore/Sandy, Goobarraganga and Goodradigbee), deterioration of the riparian zone and extractions (Hillas), minor recreational pressures and roads (Tantangara) and stock (Tarcutta). No future risks have been noted for the Shire.

The Murrumbidgee Catchment Action Plan, 1998, states that major occurrences of streambank erosion occur in the following catchments:

• Tumut River - Brungle, Killimicat, Meadow, Bombowlee and Gilmore Creeks;
• Murrumbidgee -Adelong Creek
• Hillas Creek - Hillas, Yaven Yaven, and Nacki Nacki Creeks; and
• Tarcutta Creek - Tarcutta, Umbango, mates and Keajura Creeks.

The Tumut River is particularly susceptible to erosion because of the consistently high flows from Blowering dam. The Tumut River Management Strategy 2000 is addressing erosion and channel capacity problems. The current five-year program is addressing identification and stabilisation of erosion sites and willow lopping activities on the Tumut River.

Approximately 66% of Tumut Shire falls within unregulated subcatchments. Not all subcatchments listed in Table 1 lie wholly within the Shire. Subcatchments are of differing size, in terms of area and volume of water flowing through them.

About the data

Assessments and comments on geomorphological condition and stress for unregulated streams have been provided by the NSW Department of Land and Water Conservation (DLWC). The data are reported in the Stressed Rivers Assessment Report for the Murrumbidgee Catchment. The report was published by the DLWC, in Sydney, 1999. Details about the data sources and assessment process are contained in each of these reports. A brief summary about how the geomorphology stress rating was assessed follows:

Geomorphology stress rating

For all catchments except the Murrumbidgee a stress rating has been determined where data were available. Aerial photography was used to assess the geomorphological condition, using 1996 colour coverage at 1:25 000 scale (stereo pairs). The criteria for assessment are identified in Table 2.

The Stressed Rivers Assessment Reports provide data on unregulated catchments only. DLWC has defined unregulated streams as "those which do not have major rural dams, primarily for irrigation supply downstream and therefore most water users rely on natural flows for their water supplies" (DLWC, 1999:1). Flows in unregulated streams however, can be and are still affected by town water supply, hydro-electric dams, weirs and other water diversions.

Data on streambank erosion were also sourced from the Murrumbidgee Catchment Action Plan, 1998. The plan was prepared and published by the Murrumbidgee Catchment Management Committee, Wagga Wagga, NSW.

Description: What does 'streambank disturbance' measure?

Which data are collected?

• length and proportion of streambanks disturbed (expressed in terms of 1st, 2nd, 3rd stream order)

Why do we report this indicator?

Change in the dimensions of streambanks is a natural process. These changes are thought of as streambank disturbance when the rate of change is accelerated by human activity.

The main causes of streambank erosion in the Region are changes to streamflow and destabilisation of the streambanks by some recreational uses, removal of riparian vegetation and livestock trampling of the banks. Further, the loss of land associated with streambank erosion means that, apart from the potential destruction of infrastructure such as roads and bridges, that land is no longer available for landuses such as farming or urban development.

Livestock can degrade the in-stream habitat directly by trampling the streambed and adding pathogens and nutrients from their faeces. It is an indicator of the pressure of some landuses and land management practices on streams.

The easiest strategy to avoid this pressure is to construct fences so that livestock are excluded from the riparian zone. Knowledge of the length of streambank and associated riparian zone with stock-proof fencing indicates the severity of this pressure on streambanks, and the rate at which it is being addressed.

The rate and extent of streambank disturbance is of interest to State of the Environment reporting because of the impact on the human and natural environment. As banks erode, valuable habitat for aquatic fauna is lost and sediment is added to the stream for subsequent transport and deposition downstream. This has an obvious impact on stream water quality.