A preliminary modeling study on morphodynamic equilibrium of tidal channels floored with sandy sediments

A morphodynamic equilibrium associated with tidal channels,a common feature on continental shelves or in shallow marine environments,plays an important role in the coastal engineering.The mophodynamic equilibrium and the length of time required to reach equilibrium for tidal channels floored with sandy sediments were modeled on the basis of a one-dimensional process model incorporating Bagnoldps formula for a bedload transport rate(as modified by Hardisty) and the mass conservation equation,taking into account the effect of bed slope.It is assumed that tides are predom inant hydrodynamic forcing and the seafloor is flat at the initial stage with a uniform grain-size.Numerical experiments have been carried out to investigate the impact of the various controlling factors on equilibrium,including flow field characteristics,currentvelocities,durations of flood and ebbtides,and the grain-size of sediment.The results show that on a time scale of 100 a equilibrium may be reached.There exist negative feedback mechanisms between flow and bathymetric changes.Any mophodynamic equilibrium state can be related to a combined condition of flow field characteristics which control the eventural equilibrium configuration of bed profile,sediment grain-size,current velocity and flood or ebbduration.Maximum scour depths associated with equilibrium are sensitive to the current velocity but insensitive to the grain-size or the flood/ebb duration.However,the time span required for the channel to reach the morpho dynamic equilibrium is sensitive to the grain-size and the flood/ebb duration,in addition to current velocity.