Sea-Going Navigation Channel Sedimentation Formula

Navigation channel is one of the main components of any harbor that it facilitates the access of ships to harbor. The depths of most navigation channels gradually decrease over time due to sedimentation since these channels behave as a sediment trap. Periodic maintenance is required to remove sediment trapped in navigation channel to maintain the required depth of channel. Maintenance costs are a critical element in the economic feasibility of a port, particularly when a relatively long access channel requires frequent dredging. So, sedimentation problem in navigation channel is considered a crucial issue according to economical and environmental point of view, which depends on geometric of navigation channel and hydrodynamic parameters.

Sediment movement and tidal/wave conditions are balanced in most natural systems. Many natural systems are equilibrated and free of sedimentation or scour. Sedimentation occurs when flow velocities are not strong enough to keep sediment moving (usually a result of deepening for navigation/harbor development). Sediment deposition is close related to the exchange water between the basin and the surrounding environment.

When a navigation channel is deepened and widened on a shoal, the sedimentation on the channel is the result of sediment movement change caused by the movement of wave and tide on the shoal. To estimate the sedimentation on the channel, one needs to study the sediment transport and find a unit sediment transport rate based on the measured data. Then, the sedimentation formula is derived based on the assumption of the sedimentation induced by the sediment transport capacity reduction due to the navigation channel deepened and widened on the shoal.

Shanwei Harbor is located on the northeastern of Hong Hai Bay, China and entrance of Pin Qing Lake. Pin Qing Lake is a lagoon with area of 22 km2. There are no major rivers flowing into the lake. The harbor is the system of lagoon, tidal channel and sand bar. The harbor is in the 3 km channel and behind 1.8 km sand bar, and water depth is above 5 meters. There is a lot of shoals outside the tidal channel. The harbor would be expanded into medium-sized one of 3000 to 5000 tons. One of key issues was the sedimentation after the sea-going navigation channel from the harbor was deepened and widened.

The shallow water equations were used to simulate the two-dimensional depth-averaged tidal flow before and after the navigation channel was deepened and widened with the hydrological data of spring tide in November of 1988. And the sedimentation formula developed in this article was adopted to estimate annual sedimentation rate to show that it was feasible to expand Shanwei harbor into the medium-sized one of 3000 to 5000 tons.