Factors controlling tidal inlet stability are analysed and the general dynamic behaviour of an inlet in response tn hydrodynamic and sediment dynamic conditions are discussed, using an example from Christchurch Harbour (southem EngEand) 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 resuhs show that: (1) the Ω/M ratio as one of stability cnteria can be extended to include the influences of the charaeterislies of ddas and freshwater discarges: (2) for inlet systems eharaeterised by small flood and ebb tidal deltas and a pattern of by-passthg of sediments due to tidal currents, the equilibrium cross-sectional area can be dateminthed analytically; (3) the ratio of the difference belween flood and ebb sedimem discharges within the entrance to longshore sediment flux (i.e the parameter k defined in the present study) can be used as a stabi fity criterion; and (4) the evolution of an inlet system in response to an increase in longshore seth mere flux appears to be characterised by a de creasein AE and a constanl k value in early stages, but by a stow change in AE and a daereaease in kin laterstages (hence, these two stability erileria can he combined to describe [he inlet behavicurs in response to sediment movemenl. for different stages of evolution)

A simple approach to the estimate of long-term sediment discharge through an entrance to a tidal basin is descrihad. Using the method, cross-sectional mean current speeds are derived, on the basis of the definition of an 'apparent tidal basin area', from records of water levi data from a single tide gauge The obtained time-series of current speeds are then used to define 'local' current speeds, through the use of a sectional distribution function for the currents. Sediment transport formulae are then applied, using the obtained speed data and other relevant parameters contained within the formulae and frequency distribution functions with regard to wave and tidal current characteristics, to estimate sediment discharge through the entrance. Analytical procedures of the method are described in detail, in an example from Christchurch Harbour (southern England).

The relationship between the flux of exotic benthic foraminiferal tests (i.e. tests which are supplied from open-sea sources alone) in a tidal inlet and that of bulk sediment was analysed, which can be expressed as two first-order linear equations. According to this relationship, in order to determine net sediment transport directions in the entrance, the test concentration in surficial sediments of the tidal basin can be compared against a 'critical level'. The critical level is etermined for the conditions that no net transport of bulk sediment is present within the entrance. If the observed concentration (averaged over the tidal basin) is higher than the simulated critical level, then the net sediment transport is directed to landward. This method is applied to the analysis of net sand transport at Christchurch Harbour, a tidal inlet system located in southern ngland. In this investigation, concentrations of exotic foraminiferal tests in the surficial sediments of the tidal basin and ebb tidal delta area were obtained from the analysis of sea-bed sediment samples. A series of probable critical levels were calculated based upon the data sets with regard to: (1) sediment discharge from the rivers; (2) magnitude of sediment discharge within the entrance during the ebb; (3) the test concentration outside the harbour; (4) the thickness of the moving layer; and (5) two parameters associated with dispersive processes. The results show that the concentration in the tidal basin sediment is higher than a number of simulated critical concentrations for representative cases. Consequently, the high level of the concentration of exotic benthic foraminiferal tests within the harbour should be explained as a result of landward net transport of sands within the entrance.

Water and sediment movement in The Wash embayment has been determined from an extensive set of data, consisting of tidal current readings and suspended sediment concentration measurements. Instantaneous and residual currents in the embayment show a distinct lateral inhomogeneity, Whereas vartically the water column is almost homogenous. The central deep water area (30-40m) of the embayment is dominated by a residual landward water movement, whilst on the margins, the residual movement is seaward. Sediment is supplied predominantly in suspension from the north, through the northern extremity of Boston Deep. Suspended sediment pathways are coincident with the spring tide water movements and the subtidal channels act the main conduits. Approximately 6.8×106 thonnes yr-1 of suspended sediments are supplied to the embayment from offshore areas. Bedload sediment supply is of lesser importance, ≈1.4×104 tonnes yr-1. Whereas suspended sediment movement appears to be the dominant mode of transport throughout the embayment, bedload transport is important in reforming the sea bed into a variety of bedforms which are particularly well developed on the margins of channels and shoals.