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Keeper by Name, Keeper by NatureMeet the Keeper

The Whys and Hows of Avoiding Reversals

By Tamia Nelson
tamia@paddling.net

December 13, 2011

We drew the Tripper ashore well upstream of the weir, carried around it, and then walked back to see what we could see. To be honest, I was disappointed. The four‑foot‑high dam didn't look like much, and the meltwater‑swollen stream flowed over it smoothly, descending in a graceful arc. I was sure we wouldn't have hung up on the lip if we'd continued downriver. And I certainly didn't understand why Farwell had insisted on our portaging around it.

I was about to say so when he picked up a tree limb left behind by the spring floods and flung it wordlessly into the stream, just above the dam. The limb — as big around as my arm, and longer than I was tall — was swept away by the spirited current. It reached the weir in no time, plunged unhesitatingly over the drop, and then… I lost sight of it. A frothy apron extended some eight or 10 feet below the little dam. The swirling water didn't look as if it could swallow up a whole tree limb without a trace. In fact, it seemed no more dangerous than the head on a glass of beer. But where had that tree limb gone? I couldn't see it anywhere. Seconds passed. Nothing. How could I have missed its passage through the foam? Yet what other explanation was there? So I looked downstream. Still nothing.

Then Farwell nudged my shoulder. He pointed upriver, and I turned my face back toward the swirling water. There was the limb. It lay parallel to the face of the weir, caught in an almost imperceptible crease where the froth met the plunging torrent. It wasn't going anywhere. But it wasn't exactly dead in the water. On the contrary, the limb spun round and round, like a chair leg being shaped in a lathe. I watched it for several minutes. Every so often, some imperceptible alteration in the balance of forces would pull it under. There it would remain, sometimes for many seconds, only to pop up again and resume its restless spinning.

Now I imagined our canoe alongside it, spinning endlessly. And where were we in that picture? In the cold, meltwater‑fed stream, that's where, alternately pulled down below the surface and pushed up, breathing only when the river loosened its grip on our bodies. Suddenly, I started shivering, and it wasn't because there was a chill in the spring air.

Experienced boaters will be surprised at my naïveté, I know. But this was early in my canoeing career, and I'd never before taken a close look at the phenomenon whose name I was about to learn: keeper. Seldom was a name better chosen, since …

A Keeper by Name Is a Keeper by Nature

And the warning embedded in the name is one you'd be foolish to ignore. Keepers, like sweepers, are high on the list of moving water's great gotchas, yet their apparently innocent appearance belies their danger. No one needs to be warned about the hazards of a turbulent Class V drop. One look tells even a clueless kibitzer that powerful forces are at work there. But a low dam on a Class II stream? It doesn't seem at all dangerous. Quite the opposite. You could easily be looking at a pastoral scene torn from the pages of a holiday calendar. Which is why weirs continue to levy an annual toll of inexperienced or overconfident paddlers. And weirs aren't the only places you'll find keepers. You can expect them below any reasonably regular, roughly linear obstruction that lies athwart the current, whether the obstruction is natural or man‑made — dams, ledges, even the occasional elongated boulder. Here are four examples:

Four of a Kind

There's a keeper below each of these drops, and though they vary in shape and extent (each photo includes a scale bar), they're all capable of trapping an unwary or unlucky paddler when the water level is right. Note the similarity in appearance over the threefold range in height. This phenomenon is known as self‑similarity over scale change, and it's often seen, complicating the business of scouting drops from any distance.

The vagaries of language can complicate the picture, too. Keepers are frequently known by other names. "Reversals" is one, and while "keeper" suggests the nature of the threat they pose to paddlers — remember Farwell's riverbank demonstration? — "reversal" hints at the underlying mechanism. Take a look at this cross‑section:

Cross-Section

A stream dropping over a ledge creates a vertical eddy. Along the ledge's sculpted face, water flows evenly and smoothly. But this orderly progression breaks down in the plunge pool below. Here turbulence dominates. Much of the water entering the pool's depths now rockets upward and flows back toward the ledge. This is the counterflow that gives rise to the name "reversal."

Some water always escapes, of course, but the downstream flow is largely confined to the pool's deepest depths, while the aerated water above circulates round and round, in a roiling, rolling carousel. Can you see the "crease" I mentioned earlier, when I described Farwell's impromptu streamside demo? It forms at the juncture where the counterflow surface current meets the water plunging down over the ledge, and it's where most floating debris — whether it's a discarded styrofoam cooler, a tree limb, or a bit of a broken boat — ends up. (The very bottom of plunge pools can also be a treasure trove for trash hunters. In low‑water forays I've found everything from ancient fishing lures and tangles of shot‑weighted monofilament to bits of baby carriage, along with such natural detritus as sand, gravel, and thoroughly waterlogged snags.)

Of course, it's immediately obvious that reversals have much in common with the souse holes that form below midriver rocks. But whereas souse holes are (typically) bounded on both sides by downstream‑flowing V's, a reversal stretches across the full width of the river, or near enough as makes no difference. Which is why souse holes make good play spots and reversals do not. If you mess up in a hole, you've got a good chance of being flushed downstream before you've spent too much time going round in the washing machine, but a similar mischance in a reversal can lead to a life sentence. Here's a bird's‑eye view of just such a keeper:

Bird's-Eye View

And here it is seen in the oblique:

Sidelong Glance

A lot of water can flow over this dam before an unlucky paddler (or her boat) is flushed through. And what decides whether she's fated to be washed out or washed up? Many things: the volume of water flowing over the dam (discharge), the character of the riverbed (rough, smooth, or in‑between), and the speed of the current, to name only three. But there's a surprising omission from the list. The height of the dam isn't determinative. Weirs and other low‑head dams have claimed many victims. Nor is the relationship between discharge and danger a simple one. Up to a point, the extent — and therefore the danger — of a reversal increases as the discharge increases. But flood waters can drown a dam completely, temporarily wiping the associated reversal off the map, as shown in the following sketch:

Now You See It...

Which isn't to say that paddling a river in flood is risk‑free, of course. In truth, it's one of the riskier things a canoeist or kayaker can do. But some — some — reversals are rendered harmless by floodwaters.

Now let's take a look at the middle ground between river‑wide keepers and souse holes. Here's one example. It's just about big enough to hold a pack canoe when conditions are right, though you'd have been hard pressed to float any canoe larger than a birchbark tourist trinket into it on the day I took these photos:

Test Case

The river is flowing from right to left, and the mini‑reversal in the photo is located below a rocky spur and its next‑door neighbor, a good‑sized boulder. The drop isn't much. It varies between 10 inches and a foot. Even this small a drop can cause trouble at higher water levels, though.

That sets the scene. But up till now I've skirted around a critical point:

How Do You Identify Dangerous Reversals?

This is the question, after all. One venerable rule of thumb suggests that any reversal more than four feet in extent — as measured from "crease to crest" — warrants extreme caution. Or you can try a simple field test along the lines of Farwell's long‑ago demonstration. (I don't need to remind you to exercise care in scouting reversals from shore, do I? In particular, keep your PFD on your bod, where it can do you some good if you slip. I'm sure I'm not the only paddler who's fallen into a rushing stream while scouting!)

The mechanics of the field test are simple. Find a good‑sized downed limb. In preparing photos for this article I selected one that was about three feet long and as thick as a man's wrist. Now toss your chosen limb into the water above the ledge or other obstruction and follow its progress with your eye. Its fate can tell you a lot about the character of the drop. An overview follows. (All photos were taken at the same mini‑reversal shown above. To see a somewhat larger version of the panel in a new window, right‑click anywhere inside the margins.)

By the Numbers

Since it can be hard to spot even a large limb in the foamy churn below a small drop, I've added red pointers to the photos. Now let's take a closer look, following the limb on each stage of its journey. In Photo #1 the limb is poised on the brink. (Click through the links to see enlarged images.) It goes over the drop in Photo #2, but it doesn't continue downriver. Instead, it swings round, parallel to the ledge (Photo #3) and marks time in the crease until one end drifts close to the adjacent tongue (Photo #4). The keeper isn't about to relinquish its prey so easily, though. In Photo #5, the reversal has recaptured the limb, and soon it's back in the crease (Photo #6). This game of cat‑and‑mouse continues for some time (see Photo #7, Photo #8, and Photo #9), until the limb is finally snatched away by the current (Photo #10). How long did it take for it to make its escape? About two and a half minutes. That's a mighty long time to hold your breath.

Ramp up the river's flow a bit, and even a little drop like this could mean big trouble for a careless paddler. Can we therefore agree that it's a good idea to avoid being caught in a keeper? I'm sure we can. But everyone makes mistakes, and even old hands have been known to misjudge a drop. So what happens next? A stray limb can afford to wait as long as it takes to be released, but we paddlers can't, can we? That being the case, …

What Do You Do If You're Caught by a Keeper?

Often the best response is simply to power on through. Backpaddle as you go over the drop, by all means — this helps you avoid submarining in the frothy water — but it's All Ahead Full as soon as your bow surfaces. If your boat has adequate flotation, and if the reversal doesn't extend too far downriver, you'll probably make it through on momentum alone. A towering "stopper" wave at the downstream margin (the "crest" in "crease‑to‑crest") can complicate things, however, and in many cases it will live up to its name, stopping you dead in your tracks. If this happens, the reversal will likely draw you back upriver in a matter of seconds, and since froth doesn't do much to float a boat, it's all too likely that you'll swamp and then capsize. A buttoned‑up kayak won't swamp, of course, but it's easily capsized by the conflicting currents in a reversal, and if your bombproof roll subsequently bombs, you and your boat will soon part company.

And then you're in the water. You'll probably wish you were somewhere else. A keeper that's big enough and powerful enough to dump you out of your boat is a mighty poor place to do laps. The experience is like being tossed around in a giant's washing machine. It has little to do with anything that could properly be called swimming. Just deciding which way is up will be hard enough, and breathing will definitely be a catch‑as‑catch‑can affair. Still, it helps to have a plan.

In an ideal world, there'd be a guy with a throw bag standing on shore, but still close enough to get a line out to you. And you'd spot the line in time to grab it before the wash cycle took you down again. But things in the real world often fall short of the ideal, and if that happens, it's time to put Plan B (or is it Plan C?) into action. You have two goals: (1) Avoid being knocked unconscious by your swamped boat, which will be tossing around in the same washing machine that's taken you to the cleaners, but which now weighs at lot more than you do. And (2) catch a ride out of trouble. This entails getting something — your paddle, say, or even your arm — into a strong downstream‑flowing jet. Which you can only do by swimming down toward the bottom of the plunge pool or working your way to the outer edge of the reversal. If the reversal doesn't stretch from one bank of a wide river to the other, that is. Which is why weirs are death‑traps at some water levels. There's no nearby "outer edge" when you dump in midriver, and in the time it would take you to make you way to either bank, breathing only now and then… Well, let's just say that the house odds are against you, shall we?

One thing I should mention, if only to disparage it. Some old books recommend removing your life vest in a keeper, to make it easier for you to swim to the bottom of the plunge pool and catch that freedom ride on the downstream current. This sounds plausible, but it's really a Very Bad Idea. For one thing, in the airy froth of a reversal your PFD won't do much to hinder you when you try to dive down in search of deliverance. Quite the opposite. Whenever you need to breathe — and it's a hard habit to break — you'll find yourself wishing your vest were a lot more buoyant than it is. More importantly, though, you'll need your PFD when the reversal finally spits you out, exhausted and disoriented. That's when you'll want all the help you can get just to hold your head above water. The bottom line? Your PFD is your friend. Don't abandon it.

Let's recap the Get Me Outta Here! Drill now. I'll keep it short and tweet. You're out of your boat, splashing around in the froth below a ledge, and it's clear the river wants to keep you there. What do you do next? These four scenarios pretty much exhaust the options:

  • Are you near an edge, with a muscular tongue of water just out of reach? Then thrust your paddle into the current and hang on.

  • Lost your paddle, but still near an edge? Swim for it!

  • No edge nearby? Then reach deep with your paddle blade and flag a lift downriver.

  • Lost your paddle and no edge handy? Dive down and hope to catch a ride out of town.

That's about two tweets' worth of text, actually. But it's still pretty short. Which is a good thing. Because time is not on your side when you're sloshing about in a giant's washing machine.

Is there a better way? You bet there is. The old cliché was never truer:

Prevention Is Better Than Cure

There's just no substitute for local knowledge. Scout all drops before running them, and line or portage anything that looks like trouble in the making. If in doubt, apply the four‑foot rule. But don't assume it to be infallible. Rivers in flood — or near it — and water that's cold enough to warrant a wetsuit demand extra care. It's easier to walk away from trouble than swim away from it, after all. And don't we suffer enough reversals in life as it is?

 

In Deep

 

Weirs and waterfalls look good in calendar scenes, but you don't necessarily want to put yourself in the picture. Particularly if you're swimming. Whitewater boaters soon learn that the frothy aprons below low dams can mean trouble. In fact, they call them "keepers," and the name couldn't be more apt. Now you know why. A keeper by name is a keeper by nature. And make no mistake: It pays to keep out of a keeper's clutches.

 


 

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Copyright © 2011 by s Hoop Productions. All rights reserved.






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