Reading the River
Eddies, Up Close and Personal
By Tamia Nelson
September 16, 2003
Reading water is Job #1 for all river paddlers,
from the canoeist who's happy drifting lazily through Class I riffles to the
kayaker itching to challenge steep Class V drops. No river is a featureless
sluiceway, and no two rivers are alike. The Battenkill of
my youth was an intimate, meandering pool-and-drop stream, very different
in character from the big rivers of the American West. Despite their obvious
differences, however, the Battenkill and the Colorado have many things in
common. One of these is the eddy.
What is an eddy? In simplest terms, it's a place where the current of a
river slackens suddenly, or even reverses itself. Eddies are characterized by
circular flow patterns. A whirlpool is a kind of eddy, but the eddies that
most paddlers know best are the ones that form on the downstream side of
obstructions in a river.
Examples abound. Midstream boulders create eddies, whether or not the
boulders are visible above the surface. So do downed
piers, and projecting rock ledges. Eddies also form at the inside
of every bend in a river. And even when the channel runs straight as a
die, there are weak eddies along the bank on either side, where friction robs
the rushing water of some of its force and speed.
In short, expect eddies anytime something gets in a river's way, slows it
down, or forces it to make a turn.
Want a demonstration? You can find one as close as the nearest culvert,
parking lot, or drainage ditch. The next time a rainstorm sweeps through your
area, look for a thread of running water. It doesn't matter how small it is.
Just follow the main current with your eye. See how grass clippings and other
debris collect in tiny swirling pools below every pebble, and on the inside of
every bend? Those are eddies.
Let's get back to the
river. Check out the big boulder in midchannel. The river flows around it,
right? But water piles up against the upstream side, too. That's the
cushion. True to its name, you can sometimes rely on it to soften the
blow if you misjudge your line of descent and slam into the boulder. But don't
count on it. The cushion is stuffed with rock, after all!
And what happens downstream? The boulder splits the river into two parts,
but the filaments of water are reunited almost immediately. Then, impelled by
gravity, some of the flow surges back to fill the "hole" in the river. The
result? An eddy is born.
Of course, no two eddies are exactly alike. If a river is lazy and
slow-moving, its eddies will be equally languid, their ill-defined margins
marked only by minute, almost imperceptible whirlpools. Such eddies are easy
to drift into on lazy summer paddles. This isn't the case when a river rushes
pell-mell down a steep valley, though. Here the eddies take on a more muscular
character. They're now maelstroms of sloshing spume, and their boundaries
("eddy-lines") form heaving barriers. There's often a pronounced drop or
"step" at the edges of the larger eddies, too. You won't drift into these
eddies unaware! You'll have to drive hard to cross the eddy-line, leaning your
boat as you enter to avoid being flipped by the powerful reverse flow. And
you'd better watch out for a rough landing. If you're not prepared, the eddy
will thrust your boat up against the boulder at its head and send you
sprawling forward into the bargain.
Still, a rock doesn't have to stand tall to have an eddy below it.
Submerged rocks can also play the game. It's "invisible" eddies like these
that most often take summer paddlers by surprise on easy water. "Why have we
stopped?" they ask themselves, as they spin slowly around in midchannel, their
paddles on their knees, going nowhere. And then they catch sight of a sunken
rock just a few feet upstream. The mystery is solved. They've blundered into a
"slick." It's not a big deal. There's no better place to take a picture or
two, drink some
water, or have a bite to eat.
Once they've tired of going nowhere, they just pick up their paddles and move
When big, fast rivers wash over submerged boulders, however, it's a whole
'nother scene. Such wash-overs produce huge, boat-eating "souse holes," with
powerful vertical currents. Experts find them exhilarating playgrounds,
but most beginners would rather face rush-hour traffic than deliberately enter
one of these midriver Maytags.
Happily, there's a broad middle ground between placid slicks and churning
souse holes. That's where you'll find the "friendly eddies," welcome refuges
amidst the swift currents of whitewater rivers. They're good places to stop
or bail, or
catch your breath. Let's take a closer look at one example, made a little more
complicated by the presence of a second rock in the eddy, with an eddy
all its own. This is a common occurrence, but you needn't lose any sleep over
it. If the main eddy is large enough, the second rock won't cause any problems
for alert paddlers. In fact, if the parent eddy is really big, it's simply
another opportunity to play the river.