Modeling of river width variations based on hydrological, morphological, and biological dynamics

One-dimensional (1D) models can be applied, for engineering purposes, to long-term and large-scale morphodynamic simulations of entire river systems only if appropriate simplifications are introduced. This paper proposes an improvement of an existing simplified 1D model based on the local uniform flow hypothesis, coupled with a synthetic description of the transverse profile, which provides the active river width by analyzing the total and the vegetated widths of a watercourse, with assumed variables of the water flow. The overall density of the riparian vegetation, expressed in terms of biological carrying capacity, is predicted as a function of the local climate and some stresses due to interaction between hydrology, morphology, and biology. The constitutive equations have been deduced and the relevant parameters have been calibrated and validated against various hydrological and geometrical data, taken by satellite imagery covering two large watercourses located in tropical and subtropical areas (Parana and Zambezi rivers) and small streams located in temperate zones. The work confirms the opportunity to deal with hydro-morpho-biodynamic river modeling at large spatial and temporal scale through a mixed 1D + quasi-2D approach. The 1D submodel permits long-term computations at watershed scale of the river longitudinal evolution, while the quasi-2D submodel provides the transversal description of the watercourse in terms of vegetated and nonvegetated widths and vegetation density, which in its turn reflects on the 1D computations.