AN IDEALIZED LONG-TERM MORPHODYNAMIC MODEL OF A TIDAL EMBAYMENT

A model is discussed which describes the interaction between tidal cur rents, sediment transport and bedform changes in a one dimensional sho rt embayment with a constant width. The water motions are described by the depth-integrated shallow water equations. They,are forced by pres cribed free surface elevations at the entrance which consist of a basi c tide and a first overtide. For the sediment dynamics both a bedload and a suspended load transport model are considered. The sediment bala nce is averaged over a tidal period to retain only the long-term behav iour of the bottom profile. The equilibrium profiles are calculated an d the stability properties of these profiles are studied for various c ombinations of the model parameters. If the forcing does not contain o vertides the suspended load model has a unique stable equilibrium whic h represents a constantly sloping bottom with zero depth at the closed end and spatially uniform tidal currents. In contrast the equilibrium profile of the bedload model is a flat bottom. The introduction of ov ertides in the forcing results in more complex dynamics. The equilibri um bottom profiles in the suspended load model can be convex or concav e, depending on the ratio of advective and diffusive transports. Solut ions of the bedload model tend to a bottom of constant slope where the water depth at the closed end may be finite. A physical interpretatio n of these results is also given.