Tidal Inlets Housekeeping

A tidal inlet on an alluvial shore presents a littoral barrier which must be overcome by flushing and bypassing of material. Presumably, the tidal inlet arranges itself in the most practical way by providing the highest flushing ability at the least loss of energy to bottom friction. This, however, is not the only condition for stability of a tidal inlet. There must be enough tidal flow available to accomplish the task of transporting all the littoral material which entered the inlet. This requires a tidal prism and discharge of a certain size compared to the quantity of littoral drift which is carried to the inlet. Part of this material may be transferred across the inlet entrance on a bar or shoal. In the inlet channel, a bottom shear stress which corresponds to a velocity of about 1 m per sec results. At this velocity, sand bottom with 0.15 mm to 0.3 mm sand changes its geometry by flattening the dunes approaching plane bottom. Both tangential and normal forces contribute to the drag of a duned-bed stream. Because the tangential forces contribute directly to sediment transport, the drag force of the bed on the stream is more effectively used to transport sediment with flatter dunes and plane bottom.