Flow in a strait or canal joining two water bodies whose tides differ in time or range, so that water runs downhill from the higher to the lower end. Speed tracks the head difference rather than the local rise and fall, and slack occurs when the two ends are briefly level, which can be far from local high or low water. Canals and straits joining two differently timed tides are the classic examples.
The canal runs a hydraulic current, so check both end gauges, not the tide at the middle.
Also heard as
- head-driven current
Related terms
Tidal current
The horizontal flow of water that accompanies the rise and fall of the tide.
Slack water
The short lull when a reversing current almost stops while it swaps between flood and ebb.
Reversing current
A tidal current that runs back and forth along one line, flood one way and ebb the other, with slack at each change.
Tidal gate
A headland, strait or bar that can only be passed comfortably at certain states of tide, fixing the timing of a passage.