Geomorphic controls on the physical and hydrologic properties of soils in a valley floor

Abstract

The distribution of soil hydraulic and physical properties strongly influences runoff processes in landscapes. Although much work has been done to quantify and predict the properties of hillslope soils, far less is known about the distribution of soil properties in valley floors. A technique that links the estimation and distribution of soil hydraulic properties in valleys, with easily identified geomorphic features, was developed along a 2 km length of a valley at Brooks Creek in New South Wales, Australia. Soil physical and hydraulic property data were collected across a set of floodplain and fan features within the valley and analysed statistically to determine if soil properties varied significantly between geomorphic features and stratigraphic layers. The results show that the depth-averaged saturated hydraulic conductivity, K(s), of the soil varies significantly with landform: fan units have K(g) values that are twice that of floodplains and colluvial toeslope deposits have K(s) values four times higher than floodplains. Given the notorious variability of K(s) values in space, the strong statistical separation of soil properties by landform, backed up by strong separation of soil particle size by landform, suggests a way forward in understanding the distribution of soil properties in valleys and their influence on catchment hydrology.