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.