Sediment transport, redistribution and storage on logged forest hillslopesin south-eastern Australia

Post-logging changes in catchment sediment yield have traditionally been at tributed to increases in hillslope erosion and delivery rates as a result o f forest harvesting activities. Linking hillslope erosion to catchment yiel d in forestry environments remains difficult, however, primarily because of the scarcity of data on the nature of hillslope sediment storage and deliv ery processes. A large rainfall simulator (350 m(2)) was used to apply rain storms to a logged hillslope containing a snig track (skid trail) and a gen eral logging Or harvesting area (GHA) on 10 forest compartments in south-ea stern Australia. The experiments confirmed that the compacted, disturbed su rfaces, such as roads and tracks, are the dominant sources of sediment in f orestry areas. Sediment transport rates were limited by available sediment supply on both the snig track and the GHA, introducing important implicatio ns for the modelling of these surfaces using sediment transport capacity th eories. Sediment delivery from the snig track to the adjacent GHA, via a cr oss-bank (drainage diversion), was strongly influenced by the percentage fi ne fraction in the eroded sediment. Preferential deposition of coarse aggre gates was measured at erosion control structures and on the adjacent GHA. O ver 50% of fine-grained material were deposited on the hillslope over a rel atively short, flow path length of <5 m, highlighting the effectiveness of runoff diversion as a practice in reducing sediment flux. The transfer of w ater and sediment from disturbed to less disturbed parts of the landscape, and the associated potential for sediment storage, needs to be considered a s part of any catchment impact assessment. Copyright (C) 1999 John Wiley & Sons, Ltd.