Comparing model predictions of hillslope sediment size distribution with field measurements

Hillslopes produce the sediments that are supplied to river channels’ bed. The river bed sediments link climatic factors to landscape evolution by regulating the rate of river incision. However, the factors that control hillslope sediment size are poorly understood, limiting our ability to predict sediment size and model the evolution of sediment size distributions across landscapes. Recently separate field and theoretical investigations have begun to address this knowledge gap. Here we compare the predictions of several emerging modeling approaches to landscapes where high quality field data are available. Our goals are to explore the sensitivity and applicability of the theoretical models in each field context, and ultimately to provide a foundation for incorporating hillslope sediment size into models of landscape evolution. The field data include published measurements of hillslope sediment size from the Kohala peninsula on the island of Hawaii and tributaries to the Feather River in the northern Sierra Nevada mountains of California, and the Inyo Creek catchment of the southern Sierra Nevada. These data are compared to predictions adapted from recently published modeling approaches that include elements of topography, geology, structure, climate and erosion rate. This research suggests that models may be suitable for predicting sediment size distribution, given adequate data for environmental factors and the initial size distribution is available.