Prompted By A Thread About Waves In Rivers...

[sandyRoe]

Would it take much of a current or undertow to pull a swimmer under water?

[Eve]

It would depend on the swimmer as well as the water conditions.

[sandyRoe]

The human body doesn't seem to be very buoyant. People floating in water sometimes have no more than their face above the surface. I thought that it wouldn't take much of a current to pull someone under.

[jno]

depends how strong the swimmer was.

I remember in the Marchioness sinking, bodies were washed up in Hammersmith, 8 miles upstream. But the Thames is tidal, the North Sea pouring in, and the current is very strong.

[jomifl]

Sandy I suspect that the concept of an 'undertow' is a bit fallacious. Water usually flows because of gravity and normally it would all flow at the same speed except for friction at the bottom and sides of a channel. This means that for example in a river the current is strongest in the middle and at the surface. This breaks down along the surf line on beaches where the water is extremely turbulent and swimmers can become disoriented and have difficulty staying at the surface long enough to breathe. Also large amounts of water are being dumped on the beach and this flows out to sea along paths at right angles to the shore which develop in spacing and strength according to the conditions. Bathers sometimes get caught in these currents and are carried offshore quite quickly.