Abstract

Predicting the equilibrium cross section of natural rivers has been widely investigated influvial morphology. Several approaches have been developed to meet this aim, starting from regimeequations to the empirical formulations of Parker et al. (2007) and Wilkerson and Parker (2011), whoproposed quasi-universal relations for describing bankfull conditions in sand and gravel bed rivers.Nevertheless, a general physics-based framework is still missing, and it remains an open issue to betterclarify the basic mechanisms whereby a river selects its width. In this contribution we focus our attentionon lowland rivers with cohesive banks, whose resistance to erosion is crucial to control the river width. Inparticular, we formulate a theoretical model that evaluates the equilibrium width of river cross sectionsmodeling the interaction between the core flow in the central part of the section and the boundary layerthat forms in the vicinity of the cohesive banks. The model computes the cross-section equilibriumconfiguration by which the shear stresses on the banks equal a critical threshold value. These stresses arecomputed by partitioning the total shear stress into an effective grain roughness component and a formcomponent (Kean and Smith, 2006a). The model is applied to a large data set, concerning both sand andgravel bed rivers, and it is used to determine the relations expressing the channel width and the bankfullflow depth to the bankfull discharge, which appear to provide a unitary description of bankfull hydraulicgeometry.

Citation

Francalanci, S., Lanzoni, S., Solari, L., and Papanicolaou, A.N. (2020): Equilibrium Cross Section of River Channels With Cohesive Erodible Banks. JGR Earth Surface. DOI: 10.1029/2019JF005286