Tidal Inlet Equilibrium, in Relation to Cross-sectional Area and Sediment Transport Patterns

Equilibrium cross-sectional area is a crucial parameter in the assessment of the stability of tidal inlets; it has been related to tidal prism, through the empirical O'Brien method. Analyses presented here, based upon equations associated with equilibrium, show that other factors (i.e. not tidal prism alone) are also important: (1) flood and ebb tidal durations; (2) freshwater discharges; and (3) sediment transport through the entrance. Analytical approaches are suggested for evaluating tidal inlet equilibrium conditions. The method can be applied to analyse the equilibrium of individual inlets, reducing errors in the application of the O'Brien method. Equilibrium conditions for inlet systems at Langstone Harbour (southern England) and Yangpu Harbour (southern China) are compared, suggesting some deviation from the conclusion that maximum cross-sectional mean current speed for a stable inlet should be around 1·0 m s-1