A gradient or mosaic of patches? The textural character of inset-flood plain surfaces along a dryland river system

Abstract

This paper investigated the textural character of surface sediments across a range of inset-flood plain surfaces on the Barwon Darling River, Australia. Surface sedi­ments ranged in size from clay to coarse sand (-1Φ - <4.75Φ) but varied in composition between different inset-flood plain surfaces. Multivariate entropy analysis detected five sediment classes based on the grain size distributions of individual samples. River channel sediments were present in two of the entropy classes, whereas the different inset-flood plain surfaces were present in four or more of the identified entropy classes. A number of factors may be influencing the spatial distribution of sediment texture across the inset-flood plain surfaces including: (1) decreasing energy gradients with increasing elevation from the channel; (2) variable sediment supply conditions during flow events; and (3) local sediment inputs. The resulting patterns found in the study area demonstrate there to be a mosaic of sediment texture patches rather than a simple gradient of changing sediment texture with increasing distance from the channel.