Laboratory observations of the morphodynamic evolution of tidal channels and tidal inlets

This paper tackles the problem of morphodynamic equilibrium of tidal channels and tidal inlets. We report a laboratory investigation of the process whereby an equilibrium morphology is established in a tidal system consisting of an erodible channel connected through an inlet to a tidal sea. Observations suggest that a morphodynamic equilibrium is eventually established both in the inlet region and in the channel. The latter exhibits a weakly concave bed profile seaward, a weakly convex profile landward, and the formation of a “beach” close to the landward end of the channel. A second set of observations concerns the formation and development of both small- and large-scale bed forms. In particular, small-scale forms are found to develop in the channel and in the basin, while larger-scale forms, i.e., tidal bars, develop in the channel. A last observation concerns the formation of an outer delta in the “sea” basin. Results concerning the long-term equilibrium of the bed profile in the channel compare fairly satisfactorily with recent theoretical results. The nature and characteristics of the observed small-scale forms appear to be consistent with theoretical predictions and field observations concerning “fluvial” ripples and tidal dunes; bars show features in general accordance with recent results of a stability theory developed for tidal bars. The hydrodynamics of the inlet region exhibits a strongly asymmetric character, as observed in the field and predicted in early theoretical works, while the overall characteristics of the outer delta conform to available empirical relationships.