Effects of alpine ash logging on stream sediment levels in the East Kiewa River catchment. 2. First calibration report.  C. J. Leitch.  June 1981.  30 pp. (unpubl.)

SUMMARY

Early in 1978, an experimental catchment study was established on two adjacent tributaries of the East Kiewa River in north-eastern Victoria to determine whether logging of Alpine ash (Eucalyptus delegatensis R. T. Baker) forest affects stream sediment levels. Before harvesting commences, the two streams, Springs and Slippery Rock Creeks, are being studied in their undisturbed states to establish the natural sediment relationships within and between the two catchments. This report represents an analysis of the rainfall, streamflow and sediment yield data that have been obtained during the calibration so far.

The analysis shows that, for the range of streamflows that occurred between May 1978 and September 1980, a high correlation exists between the sediment yields of the two creeks (weekly: r = 0.863; monthly: r = 0.893; storm: r = 0.808). Slightly higher correlations also exist between storm sediment yield and runoff for each catchment (Slippery Rock: r = 0.927; Springs: r = 0.941). Further statistical analysis of the monthly data shows that the post-treatment mean of the ratio of monthly sediment yields of the two creeks would need to be 14% higher than the equivalent mean of the pre-treatment data, for the effect of treatment to be judged significant at the 95% confidence level.

Although an average number of days of high rainfall were recorded during the period of study, there were few sustained periods of the heavy rainfall that is usually associated with high stream flow. Therefore, there is a high probability that peak streamflows after treatment will exceed those recorded so far. For this reason, a study is being made of the volume and distribution of sediment in the stream channels to provide information on the sources of sediment yielded from the catchments. Data from this additional study, together with the knowledge of sediment behaviour gained during the ongoing calibration period, should provide reliable estimates of the effect of logging activities on stream sediment levels for a wide range of climatic events.