Safe and reliable access to ports is essential to compete with the increasing size of ships that ports want to attract. However, capital and maintenance dredging are expensive and it can therefore be a considerable advantage to apply the latest technology in both designing and operating an access channel.
The factors that determine the required dredged depth include:
- The volume of traffic expected and the split between ships of various types and draughts;
- The tidal range;
- The wave conditions and their persistence;
- The type of seabed material;
- The currents and winds;
- The speed of the ship;
- The level of sophistication of the admission policy.
BMT has tools for designing channel depth ranging from very simple approaches to sophisticated probabilistic design accounting for all the above factors. This is underpinned by in depth knowledge of:
- Squat, trim and heel;
- The effect of winds and currents on the orientation of the ship;
- The vertical movement of the ship in response to waves and the associated distributions;
- Wind, waves, currents and tides.
The use of a sophisticated admission policy, allows ship access for a higher percentage of the time with a higher degree of safety than a simple system based on a limited number of simple criteria. A consequence of this is that the required dredging will be less when a sophisticated admission system is applied. An example of such a system is PROTIDE (see Bos (now at BMT SMART), Koop (now at BMT Ship & Coastal Dynamics) & Bolt, 2011 ), as applied for the ports of Amsterdam, Rotterdam and Eemshaven.
The result of a typical study is typically a recommendation for the minimum dredged depth of an access channel for a particular safety level (e.g. the probability of any ship touching the seabed in a 25 year period is less than 10%).