Field calibration of sediment flux dependent river incision

Abstract

Bed erosion and sediment transport are ubiquitous and linked processes in rivers. Erosion can either be modeled as a "detachment limited" function of the shear stress exerted by the flow on the bed, or as a "transport limited" function of the sediment flux capacity of the flow. These two models predict similar channel profiles when erosion rates are constant in space in time, but starkly contrasting behavior in transient settings. Traditionally detachment limited models have been used for bedrock rivers, whereas transport limited models have been used in alluvial settings. In this study we demonstrate that rivers incising into a substrate of loose, but very poorly sorted relict glacial sediment behave in a detachment limited manner. We then develop a methodology by which to both test the appropriate incision model and constrain its form. Specifically we are able to tightly constrain how incision rates vary as a function of the ratio between sediment flux and sediment transport capacity in three rivers responding to deglaciation in the Ladakh Himalaya, northwest India. This represents the first field test of the so-called "tools and cover" effect along individual rivers. © 2011 by the American Geophysical Union.