Al-Subiya tidal channel, Kuwait, is an example of an open-ended tidal channel located in an arid, mesotidal environment. The geomorphological characteristics and the hydro- and sediment-dynamic parameters of the channel were investigated in order to determine its process-response and morphodynamic characteristics. The investigation was undertaken using indirect (eg. remote sensing) and direct (eg. field data acquisition) methods and several types of models, namely descriptive, theoretical, statistical, empirical and mathematical models.
The adjacent terrestrial and oceanic environments, channel shape and orientation, and bathymetry influence channel processes and sediment availability. Three main suites of processes control the process-response characteristics and morphodynamics of the Al-Subiya tidal channel. In decreasing order of importance, there are tidal, aeolian and wave processes. The importance of each of these processes varies longitudinally (eg. tidal current velocities, ebb-dominance, wave energy) and laterally (eg. aeolian input, erosion and deposition) within the channel.
Tidal processes play the major role in the channel hydrodynamics and sediment budget. Tidal hydro- and sediment-dynamics are strongly ebb-dominated, with net sediment export from the channel of 4x106 tonnes/yr, although this has not been the case throughout the Holocene sea-level highstand. Aeolian inputs contribute to the channel sediment budget with 82,680 tonnes/yr as dust fallout; 20,424 tonnes/yr as bedload. The dominance of aeolian bedload along the western intertidal results in channel asymmetry and progradation of the western shoreline. Wave activities are concentrated in the southern part of the channel and contribute to transport sediments up-channel (8,442 tonnes/yr a net northwesterly longshore sediment transport). The eastward channel migration was inferred from the channel morphology and hydrodynamics, with a maximum rate of 0.30 m/yr.
The analysis indicates that the hydrodynamics of the Al-Subiya tidal channel are similar to estuarine hydrodynamic behaviour, rather than to other types of inland marine waters (eg. tidal creek). The open-ended feature of the channel is an important factor affecting tidal current behaviour and, therefore, hydrodynamic circulation and sediment transport. This feature enhances the dominance of ebb tide. The velocity of flood current entering the channel decreases as the current progresses towards the north due to the opposing flood current which enters the system from the Bubiyan channel. Thus, the opposed tidal currents contribute towards a reduction of the flood current velocities. However, the zone of divergence of ebb currents lies north (up-channel) of the zone of convergence of flood currents. As a result of this asymmetry, the ebb/flood ratio in the Al-Subiya tidal channel is increased.
Although the morphodynamics of the channel and its environs are little affected by human activities to date, development of a new city and coastal infrastructure is planned. Dredging and reclamation works associated with this development are predicted to alter the relationship between the convergent and frictional effects. Reclamation of the intertidal flats will increase convergence and reduce the dominance of ebb tide while dredging of the intertidal will increase divergence and intensify the dominance of ebb tide. Other modifications of the channel system, such as modifications of aeolian inputs, erosion patterns, wave regime and sabkhas, are expected to result from the proposed coastal development. Accordingly, a preliminary proposal for future land use patterns was developed. Under this proposal, the most vulnerable and unstable coastal areas are exempt from development.