Tidal inlet stability in response to hydrodynamic and sediment dynamic conditions

Abstract

Factors controlling tidal inlet stability are analysed and the general dynamic behaviour of an inlet in response to hydrodynamic and sediment dynamic conditions are discussed, using an example from Christchurch Harbour (southern England). A technique is developed for the estimation of current speeds within the entrance channel, on the basis of the definition of the “apparent” basin area. The results show that: (1) the Ω M ratio as one of stability criteria can be extended to include the influences of the characteristics of tides and freshwater discharges; (2) for inlet systems characterised by small flood and ebb tidal deltas and a pattern of by-passing of sediments due to tidal currents, the equilibrium cross-sectional area can be determined analytically; (3) the ratio of the difference between flood and ebb sediment discharges within the entrance to longshore sediment flux (i.e. the parameter k defined in the present study) can be used as a stability criterion; and (4) the evolution of an inlet system in response to an increase in longshore sediment flux appears to be characterised by a decrease in A E and a constant k value in early stages, but by a slow change in A E and a decrease in k in later stages (hence, these two stability criteria can be combined to describe the inlet behaviours in response to sediment movement, for different stages of evolution).