BANKFULL HYDRAULIC GEOMETRY OF MEANDERING RIVERS

Meandering rivers maintain a gross bankfull hydraulic geometry as they migrate across their floodplains. Here we present a formulation for bankfull geometry which accounts for both bed material load and washload. The model assumes a two-layer structure for the floodplain; a lower, non-cohesive sandy layer and an upper, root-rich cohesive layer in which silt and finer material predominate. The channel is allowed to co-evolve with the floodplain as it migrates. Sand transport is described in terms of a relation for total bed material load. Finer material is emplaced on the floodplain by overbank deposition, and removed from the floodplain by channel migration. Channel migration is described in terms of a) bank erosion moderated by natural armoring, and b) bank deposition associated with vegetal encroachment. The model leads to dimensionless relations for bankfull width and depth and channel slope, as functions of (among other things) washload.