Numerical and Physical Experiments to Clarify the Role of Vegetation as Sediment Capacitors in Modulating Changes in Hillslope Form

Abstract:

There is a growing interest in clarifying the significance of local versus nonlocal formulations of sediment transport on hillslopes. Some work has been done to try to match nonlocal formulations to hillslope profiles, but there is limited work on how individual processes affect hillslope geometry. One such process is dry ravel of sediment in steepland environments following storage in “sediment capacitors.” Specifically, vegetation can act as sediment capacitors which temporarily store, then release sediment upon death. We are pursuing experiments using a laboratory scale hillslope that mimic dry ravel in order to explore the influence of sediment storage and release on hillslopes. These experiments attempt to recreate the long-distance sediment motions likely in sediment capacitor release. These experiments are designed to inform models that incorporate effects of these long-distance motions on hillslopes. Initial numerical simulations, together with field observations from moraines in the eastern Sierra Nevada Mountains, suggest that shrubs can locally, temporarily ‘dam’ and store significant amounts sediment arriving from upslope. Eventually shrubs release this sediment as ravel (and possibly by other surface transport processes) downslope, including delivery to storage behind shrubs. Though these sediment capacitors are just one facet of the transport story, they may represent an important process that modulates the rate of hillslope evolution.