If I see a pillow–reaction wave pair, does this mean that there's a souse hole between the waves?

Possibly, Ric—though this isn't always true. When fast water rushes over a barely-submerged rock, the downstream eddy often takes the form of a "hole" in the river—the water level drops noticeably. When the drop is dramatic, water flows into the hole from all sides. The result is a "souse hole", and the reflux flow at the downstream margin of the eddy will take the form of a "stopper"—or, even more evocatively, a "keeper"—a large, backward-curling standing wave that breaks UPSTREAM. This combination of hole and stopper can trap an unlucky swimmer for several anxious seconds (or even longer) before he's flushed out. Skilled boaters, of course, see holes as opportunities to play the river—they often surf the upstream faces of the stoppers. This is a trick that's best practiced in company, of course, and both boater and boat should be prepared for a wild ride.

I've seen washing-machine-like turbulence in rivers below low-head dams. If you dumped in the wash below such a dam, it looks like you could go round and round just about forever. Am I right?

You sure are, Ric! ALL low-head dams and weirs are dangerous, but some are even more dangerous than others. The risk to life is greatest when the lip of the dam is smooth and the volume of water flowing over the drop is high—as it probably will be in springtime. (The drop needn't be very high, though. Six-inch-high weirs have drowned people.) A dangerous dam will have a distinctive "reversal"—a sort of trough in the river—extending four or more feet downriver from the lip, with a big stopper just below that. As the name suggests, the surface flow in a reversal is UPSTREAM, and the trough is often full of debris. Such reversals are, in effect, river-wide souse holes without exits, and they can be deadly.

All dams should be scouted before running, of course. If the reversal extends more than a few feet downstream, or if you see debarked tree limbs in it, tumbling round endlessly and stripped of all their branches, DON'T EVEN THINK ABOUT RUNNING THE DAM!

On the other hand, floodwaters can submerge a dam so deep that you don't even know it's there. But you'll have a lot of other things to watch out for in floods!

OK. Let's go back to mid-river rocks for a minute. There'll always be an eddy below a rock, won't there?

Right, Ric. There's an "island" of relatively quiet water, or eddy, below every obstruction, large or small. In gentle rivers, an eddy may be nothing more than an all but invisible "slick," with a barely-perceptible circulation. In steep, powerful rivers, however, the water in eddies often flows forcefully upstream. These eddies aren't "quiet" at all. You can even find secondary eddies upriver of rocks located within them.

Eddy-lines are sometimes hard to spot in slow-moving rivers, but in big water, eddies often become holes, and eddy-lines are marked by dramatic "steps" in the river. You can't avoid noticing them then!

When scouting a route through a rapid, you should always look for the Vs, shouldn't you?

Yes—but be sure to pick the right kind of V! An upstream-pointing V marks the location of a rock or other obstruction. The obstruction is just below the point of the V. Sometimes there'll be a pillow. Sometimes there won't. In either case, you're better off avoiding it.

A downstream-pointing V, on the other hand, indicates a "chute," or passage. Even when you find such a chute, however, you shouldn't assume that you can ride it out to the end. Often there are rocks hiding in the turbulence. Look for them! And you're likely to find a big standing wave at the bottom (near the point of the V), too. It forms when the jet of fast-moving water in the chute slams into slower water just downstream. This wave is usually just a gentle roller. In high water, though, these rollers can become towering curlers, breaking upstream. That's when a chute can be a passage into danger.

Is the current always strongest in mid-channel? Do rivers flow fastest in mid-stream?

They do, Ric, but only if you're on a straight reach and if the river isn't too wide. In big rivers, the main current doesn't follow a straight line, and the thalweg (the river's "fast lane") meanders from one side of the river to the other— even when the river itself runs straight.

OK. What about places where the river doesn't run straight, then: the water in a bend is always faster on the outside, isn't it?

True. That's why cut-banks are usually found on the outside of bends, while sandbars form on the inside, where the slower water drops some of its "burden" of sediment. The outside of a river bend also collects trees which have been uprooted by the collapse of undercut banks. These "sweepers" and "strainers" can be deadly, especially in high water. That's why prudent paddlers stay close to the inside of bends in spring.

Let's get out of the fast lane, shall we? In places where the current slows down and the water isn't too deep— less than three feet, say—it seems like I have to work harder to go anywhere. Is this some kind of drag?

It is. It's called shallow-water drag, and you'll notice it whenever you've got less than three feet of water under your keel. The magnitude of the drag depends on your speed: the harder you paddle, the more noticeable the drag. (The drag gets worse as the water gets shallower, too. It really mounts up at depths of one foot or less.)

I keep a notebook to write down the things I learn about rivers and water. Do you do this?

Sure do! Both Tamia and I keep paddling notebooks, and we have for years. We've also found that it helps to watch how water behaves in tiny run-off streams and rivulets, even if they're no wider than a few inches. Eddies, holes, pillows, stoppers, bends, bars—you'll find them all (and more) if you look closely. Drop a leaf or a twig in a tiny stream and watch it run the "rapids." You'll be surprised at how much you can learn about the dynamics of moving water.