An experimental investigation of autogenic behaviour during alluvial fan evolution

The findings from a series of laboratory experiments designed to examine the role of autogenic process-form interactions as controls on alluvial fan evolution are presented. The experimental approach follows the ‘similarity of processes’ concept and is therefore not scaled to a real world prototype. The experiments were conducted in the University of Exeter Sediment Research Facility using a 3 × 3 m fixed bed experimental table with controlled sediment and water supply fed to the fan apex, and evacuation of all sediment that passes the distal boundary. The evolution of the fan was recorded using high resolution time-lapse overhead photography to permit analysis of fan topography, flow patterns, channel migration and avulsion on the fan surface over the course of the experimental run. The qualitative observations from three experimental scenarios are discussed and evaluated in the context of current understanding of alluvial fan evolution. These demonstrate that in the absence of any change in the extrinsic variables there is an autogenic transition from sheetflow to channelised flow as the experimental fans evolve. This is consistent with theory that predicts this change in response to a decline in aggradation rate through time.