Abstract

Alluvial fans form through primary and secondary geomorphic processes. Primary processes act to transport sediment from the watershed to the fan while secondary processes re-mobilize and rework the fan surface. While primary processes on alluvial fans are well studied, secondary processes and their relationship to fan flood hazards have received little attention. The experiments described herein isolate the role of secondary processes in determining alluvial fan behaviour and morphology. We conducted four experiments, in which alluvial fans were allowed to evolve under alternating primary and secondary process periods, with different durations of secondary processes. While the secondary process duration changed, the total primary process duration remained constant keeping the total volume of sediment constant for each experimental fan. Experiments with longer durations of secondary processes generated fans with larger areas and gentler gradients. In addition, longer secondary process durations led to increased flow channelization and centralization between flood periods. These morphologic changes resulted in fewer avulsions, that occurred later during primary process periods. These results indicate that changes to the relative duration of primary and secondary process periods caused by climate change can affect fan morphology and flow behaviour.