The generation and redistribution of overland flow on a massive oxic soil in a eucalypt woodland within the semi‐arid tropics of North Australia

Abstract

There is a dearth of knowledge on the runoff processes of eucalypt woodland communities in the semi-arid tropics of Australia. The work was undertaken on a 100 m transect of a 0.8 degree hillslope typical of the 'smooth plainlands' of central-north Queensland. This paper introduces a new experimental design for measuring overland flow in such areas by way of a cascade system of unbounded runoff plots which allow the inputs and outputs between troughs to be calculated. Most storms generate overland flow. Time to overland flow ranges between 1 and 18 min where rain intensities are above 10mm hr-' and when the average detention storage of 3.6mm is exceeded. The bare soil surfaces within the scattered grass understory control the runoff generation process through the temporal variability of field saturated hydraulic conductivity. The study demonstrated that overland flow is mainly redistributed over the freely-draining oxic soil. Some areas export more overland flow than they gain from upslope (runoff), others gain more overland flow than they export (runon). Over the study period only 2 per cent of total rain is transferred out of this 100m transect as overland flow due to the short duration of storms, the relatively high soil permeability, and the low slope angle. The remainder adds to the large soil water store or deep drainage. The variability of runoff-runon over these 'smooth plainlands' highlights how results from bounded plots would be misleading in such areas.

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

“…Sediment transport on the sparsely vegetated and rough surfaces of the GHA, was dominated by relatively shallow, patchy overland¯ow with limited sediment transport capacity, as observed previously in other experiments (Bonell and Williams, 1986). Although the physical processes of episodic sediment transport over a range of distances are theoretically well studied from ®eld experiments in arid environments (Mabbut and Fanning, 1987;Bromley et al, 1997), they are not well represented in erosion prediction tools for forestry environments.…”

A sediment budget for a grazed semi-arid catchment in the Burdekin basin, Australia

“…Hillslope erosion has historically been the focus of erosion studies in the semi-arid parts of Australia, and there has been a range of studies that has investigated hillslope water and/or sediment yield processes (e.g. Bonnell and Williams, 1986;McIvor et al, 1995;Scanlan et al, 1996;Connolly et al, 1997;O'Reagain et al, 2005;Bartley et al, 2006). These studies suggest that sediment loss from hillslopes can range from 0.02 to 3 t ha − 1 yr − 1 depending on the biophysical condition of the field site.…”

Representation of landscape variability and lateral redistribution processes for large-scale hydrological modelling in semi-arid areas

“…Decreasing runoff coefficients with increasing slope length due to a large variability of soil characteristics were also observed by Bonell and Williams (1986) and Puigdefabregas et al (1998) for semi-arid and by Van de Giesen et al (2000) for sub-humid environments.…”