Runoff and Sediment Attenuation by Undisturbed and Lightly Disturbed Forest Buffers

Abstract

A runoff plot experiment found that ten metre undisturbed forest buffers removed80–90% of runoff and over 95% of sediment produced by logging skid tracks. The study was carried out on 21^º slopes in a native forest in eastern New South Wales, Australia. The experiment included three replicates of four treatments including undisturbed control, skid track, skid track + undisturbed buffer and skid track + disturbed buffer. Skid track and control plots were 20 m long by 5 m wide. Buffer plots consisted of a 20 m by 5 m skid track directing runoff to a 10 m by 5 m naturally vegetated buffer that was either undisturbed or lightly disturbed. Runoff and sediment yields from plots were monitored over two successive summers. Undisturbed buffers greatly reduced overland flow and decreased sediment yields from around 100 Mg ha¹ to less than 0.5 Mg ha^-1. Differences in both runoff and sediment yield between undisturbed buffer and control treatments were minimal and not statistically significant. Disturbed buffers achieved similarly large reductions in runoff and sediment yield in two out of three replicates. The third replicate yielded as much or more runoff and sediment than the skid track plots suggesting that disturbance increased the risk of buffer failure. The peak rate of outflow from buffer plots was generally not related to peak buffer inflow until a threshold inflow of 1.6 L s^-1 was reached, after which peak outflow and peak inflow were linearly related.