Modeling the planform development of confined meandering rivers

Alluvial rivers often exhibit single thread channels meandering through floodplains. Here we deal with “confined” meandering rivers, i.e. flowing in floodplains that are bounded by topographical or geological constraints. The lateral confinement poses a transversal limit to planform development. We employ a meander migration model to study the effect of lateral confinement on the planform evolution of meandering rivers by introducing suitable spatial distributions of floodplain erodibility. To this aim, we employ the ratio WRatio between floodplain width and meander length scale as a dimensionless descriptor of the degree of confinement. Besides the effect of WRatio, we explore the system’s behavior by varying the reference values of the channel aspect ratio, the Shields parameter and the relative roughness. Results illustrate that a large WRatio (weak confinement) promotes intrinsically longer meanders, while low values of WRatio (significant confinement) forces shorter meander wavelengths and lower sinuosities. Furthermore, the presence of confinement tends to attract consistently long portions of the river centerline close to floodplain boundaries, consistently with field observations. Modelling results on meander planform descriptors are finally compared with some existing quantitative observations on these types of meandering rivers.