Friction factor evaluation in tidal rivers and estuaries.

The Saint-Venant equations are usually used for simulation of unsteady flow in various hydraulic environments including tidal estuaries and adjacent river sections called tidal rivers. These equations form the basis of most contemporary one-dimensional hydrodynamic models. Unlike lowland rivers, tidal rivers are characterized by the high variability of hydraulic resistance during a tidal cycle. The rapid variation in hydrodynamic conditions reflects changes in the ratio of forces responsible for the water movement (gravity, inertia, friction). The expression and the parametrization of the flow resistance for the unsteady currents usually are the same as for the uniform flows. As a result, the friction slope can be calculated as the hydraulic gradient from Chezy, Chezy-Manning or Darcy-Weisbach equations. The proposed method was developed to measure, calculate and analyze the variation of the friction factor in tidal rivers and estuaries characterized by reverse flow.•The method allows to identify the range of every term in the Saint-Venant momentum equation and to evaluate the contribution of different forces causing water movement during a tidal cycle.•The experimental evaluation of the friction factor and the range of its variation is a key point for accurate hydrodynamic modeling of tidal rivers.