Which term describes a surge from incoming tide in a river?

• A. Rip current recognition
• B. Slack water
• C. Wave shoaling
• D. Tidal bore

Answer: (D)

That surge from incoming tide moving upriver is called a tidal bore. A tidal bore happens when the rising tide flows into a river and piles up against the current, forming a distinct wave front that travels upstream. It occurs in rivers with a large tidal range and a channel that narrows or shallows in a way that concentrates the incoming water, so the front of the wave becomes steep and powerful as it moves upstream. For paddlers, a bore means you can face a sudden upriver surge rather than a steady current, so recognizing when a bore is coming is important for planning and safety. The other terms don’t describe this exact phenomenon: slack water is the brief lull around high or low tide with little current, wave shoaling is the increase in wave height as waves approach shallow coastal waters, and rip currents are strong flows out to sea along beaches, not upriver tidal surges.