Effects of alpine ash logging on stream sediment levels in the East Kiewa River catchment.  3. Soils of the hydrological project area.  D. J. Hough.  April 1983.  14 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 study the relationship between logging of Alpine ash (Eucalyptus delegatensis R. T. Baker) and stream sediment levels. In March 1981, a survey of the surficial mantle (both the soil and the underlying weathered rock) was undertaken prior to logging to identify soil variability in the Project Area, especially with respect to erodibility.

Soils were sampled on the three types of bedrock present (gneiss, granodiorite and quartz diorite), and on a range of aspects and topographical features in the mixed eucalypt and Alpine ash vegetation types. The variation in surficial mantle was so complex that mapping was impracticable; however, it was found to basically consist of two layers: a lower layer of saprolite or weathered bedrock, and an upper layer formed from transported slope deposits. The saprolites were found to be massive, with texture varying from clayey sand to light, sandy clay-loam, and had a low to moderate tendency to disperse and slake. The saprolite developed on granodiorite appeared to be most prone to slaking. The upper layer contained an organic horizon, a mixed organic-mineral horizon and a predominantly mineral horizon, with a texture varying from loam to sandy clay. The organic-mineral horizon had a well-developed crumb structure and was not prone to slaking or dispersion, whereas the predominantly mineral horizon was friable, with a weakly developed granular structure, a moderate tendency to slake, and a low to moderate dispersibility.

Because of the relatively uniform erosion potential of the upper layer and the complex distribution of soils, it appears that the delineation of particular soil types according to variation in erosion potential is unwarranted. It is likely that the major factors determining the degree of erosion at any particular location will be site factors such as slope, degree of soil disturbance and alterations to the drainage network.