The contribution of the mallet hill surface to runoff and erosion in the Narrogin region of Western Australia

Abstract

Severe erosion in the Great Southern area of Western Australia has long been associated with the land class known locally as the 'mallet hill'. This association was confirmed by means of an aerial photograph survey of a representative part of the area. Use of a recycling rainfall simulator showed the mallet hill land class to yield far higher runoff than any of four adjacent upper landscape surfaces. Several factors were thought to contribute to the higher runoff from the mallet hill surface. Among these were steeper slopes, a heavier texture and water repellence of the surface soil which varied from severe in the virgin and freshly cleared state to slight or non existent in soils, which had been cleared for many years. No assessment of the relative contributions of the various factors was made, although it appeared likely that water repellence would be more important in the early years after clearing. Removal of the topsoil by sheet erosion would increase the importance of the low hydraulic conductivity of the heavy-textured subsoil in causing runoff.