Runoff generation and re-distribution in logged eucalyptus forests, south-eastern Australia

While pristine forests are traditionally regarded as environments with low runoff and low erosion potential, timber harvesting can dramatically affect surface runoff production, with some important consequences for in-stream water quality. A series of targe-scale (300 m(2)) rainfall simulator experi ments on disturbed forest hillslopes, incorporating both snig track (skid t rail) and general harvesting areas (GHA), examined runoff generation and re distribution during three sequential simulated storms on 13 sites. The simu lated storms represented 30-min rainfall events with recurrence intervals o f 2, 10, and 100 y respectively. The 13 sites were selected to represent do minant soil types and ages since disturbance. The snig tracks and GHA an ch aracterised by significantly different soil hydraulic and vegetation proper ties as reflected in the nature and magnitude of runoff production. Infiltr ation-excess runoff dominated the snig track areas, white on recently distu rbed GHA, runoff was distinctly patchy because of the high degree of spatia l variability in saturated hydraulic conductivity (K-s) and degrees of dist urbance. Surface runoff from recently constructed snig tracks was an order of magnitude higher than the neighbouring GHA. Relative differences in runo ff production between the two areas declined during extreme rainfall events . Infiltration tests also indicated that a change in the processes and rate s of runoff persists for at least 5 y after disturbance. The practice of re distributing concentrated snig track runoff at cross banks wets most effect ive for small storms. However, during more extreme events, the volume of sn ig track runoff increased and Bow velocities and transport distances increa sed as the hillslope became increasingly saturated. The varying ability of the GHA to generate runoff and absorb concentrated how from the snig track is likely to be critical in predicting both the initial hydrologic response and the recovery of a small catchment from forest disturbance. (C) 1999 El sevier Science B.V. All rights reserved.