Equilibrium Cross Sectional Area at Tidal Inlets


  • Steven A. Hughes


Tidal inlets, tidal prism, equilibrium area, movable-bed models, scale relationships, inlet equilibrium


A relationship is derived between the tidal prism passing through an inlet and the inlet throat minimum cross-sectional area. The form of the new relationship closely resembles previous empirical formulations. The main assumption in the derivation is that the maximum discharge per unit width through an inlet is at equilibrium with every depth across the minimum cross section. The derived relationship matches data from 102 U.S. inlets as well as results from 18 small-scale movable-bed models, whereas previous empirical relationships failed to match the laboratory data. The new relationship between tidal prism and equilibrium cross-sectional area is used to derive new scaling relationships for movable-bed tidal inlet laboratory models. The scaling assures that the relative balance between the turbulent shear stress acting on the bottom and the critical shear stress of the bed material is the same in the model as in prototype. These scaling relationships will allow quantitative results of complicated inlet processes to be obtained from properly operated small-scale movable-bed inlet models.