Variable depth channel

A variable-depth channel is a navigation channel that carries different authorized depths along its length rather than one uniform design depth. Depth is zoned reach by reach where the bed, the sediment regime, or the traffic differs: outer reaches in exposed water are cut deeper to cover larger wave-induced ship motion, while sheltered inner reaches need less under-keel clearance for the same draft. Tide-assisted channels are a related case, where a shallower dredged depth is offset by admitting deep-draft vessels only inside a tidal window. Each reach is designed with its own gross under-keel clearance from the design vessel draft, squat, and the local wave climate, which trims the dredged volume against a single deep cut throughout.