The analysis of the conceptual channel model shows that residual current separation occurs near the narrow part of the modeled channel. The residual current directions are opposite between the middle and the lateral part, and a stagnant area with zero residual current between them. The residual current separation near the narrowest part of the channel results in a deep trough and coarser surface sediment at the bottom. The converging function of the stagnant area results in shoals and accumulation of finer surface sediment there. Qiqu Archipelago Channel, English Channel and Texel Inlet have similar characteristics to this conceptual model of a tidal channel.
Channels are important to maritime traffic and port construction. Tidal channel mainly dominated by tidal current power. The formation of opposite residual current directions occur in deeper water depths with coarser surface sediment at the bottom near the narrowest part of the channel (Sha, 1990; Grochowski, 1993; Li, 2003).A conceptual model is designed in this paper to explore the formation mechanism of the hydrodynamics, surficial sediment and topography. Some real cases of similar channels are also described.
The analysis of the conceptual channel model in this paper is based upon previous researches (P. Hayes, 1980; Bruun, 1981; Oertel, 1988), which mention that tidal inlets have characteristics such as uniform inflows as well as jet-like outflows. These previous researches focuss on the current and topography on one side of tidal inlet (i.e. the ebb-tidal delta). When the regional tidal current is roughly symmetric and reciprocating, the two sides of the channel will have similar current dynamics, and the residual current field can be generally described. According to the residual current field, the formation mechanism of the characteristics of surficial sediment and topography in a channel can be assessed.
The plane shape of the conceptual channel model is "dumbbell" shaped with wide ends, a narrow middle reach, constant depth and a geometrically symmetric shape. The longitudinal direction of the channel is east-west. It is assumed that the hydrodynamic force in the channel is controlled by a reciprocating tidal current field. The velocity and duration of the flood and ebb tidal currents are assumed equal. The direction of the tidal current is parallel to the longitudinal axis of the channel. The flood current is westward, and the ebb current is assumed eastward.
