A Discourse of Rivers
A Tale of Two Rivers
By Tamia Nelson
December 11, 2007
I love any discourse of rivers
Izaak Walton, The Complete Angler
I've been enchanted by rivers for most of my life. The first to cast a spell over me was a fabled trout stream that ran between forested hills within easy bicycling distance of my childhood home. This river of my youth started out as a boisterous Green Mountain rill, hurried along through the western ramparts of the Taconic Range, and then slowed down to meander patiently past farm fields and pastures and tiny, tucked-away hamlets, only to make a last dramatic plunge into the historic Hudson. Every bend revealed new vistas, and I came to love my river's many faces the gravel bars under the railroad bridges, the deep pools dimpled with mayfly and caddis hatches and overlooked by white clapboard houses, the chatty riffles, the brusque and bony drops. Each was the centerpiece of a scene right out of a Norman Rockwell painting. And many were just that. Rockwell once made his home on the river's very banks.
The water that flowed in my river had its changeable moods, as well. One minute, it was nibbling away at the banks. In the next, it was lapping softly against a sandbar, augmenting the 'bar's perishable store of sediment, grain by tiny grain. Yet there was seldom any violence in the flow no tumult, no thunderous clash of towering waves. The water sprinted out of the Green Mountains like a newborn foal on his first canter, playful and full of adventure. And like a foal, it was soon exhausted. Its legs folded under it, its head drooped, and it dozed. The river's energy waxed and waned with the seasons, too, though it seldom went to extremes. In spring it swelled with snowmelt, spilling out of its bed to flood cornfield and hamlet alike. But the river dropped as quickly as it rose, subsiding gently back within the confines of its banks, where it remained throughout the summer months, flowing steadily. As the sun climbed higher and temperatures soared, the water remained delightfully cool. We kids gathered in noisy mobs along the shore to swim and play, while trout congregated in the chilly depths of the many spring-fed pools.
Later, in my teens, I journeyed north, away from the valley in the shadow of the Green Mountains, and kept company with a new river, a turbulent mountain torrent whose channel had cut deep into some of the oldest bedrock on the planet. This was no languid, pastoral stream. In spring, its tannin-stained Adirondack waters coursed swiftly between sheer cliffs, exploding in showers of spray against boulders the size of small cars. Wearing the high-top sneakers that were the nearest thing I had to climbing shoes, I clawed my way up onto the cliffs, and there I discovered mysterious, smooth-walled potholes. As I caught my breath on one of the many ledges overlooking the rushing water, I marvelled at the river's power to reshape the landscape even to the extent of carving chambers in solid rock.
By late summer, however, this muscular mountain river had spent most of its force. Just a few months ago it had roared. Now it merely whispered, a tepid trickle threading its way hesitantly between the same glacial boulders that it had earlier torn from the flanks of the ancient Adirondack hills and then rolled for miles along its bed.
Those were the two rivers of my youth, separated by no more than 60 miles. And though I'm no longer young, these rivers show no signs of aging. Water still flows in each, driven by the same imperative the irresistible tug of gravity. Yet these two rivers are as different as they are alike. This won't come as a surprise to anyone who spends time in a small boat, of course. But some questions come unbidden to us all. So let's try to answer them. That's the starting point for our
Discourse of Rivers
Pick any place on any map, and chances are good that a river runs through it (or near it). All but the driest of deserts are crisscrossed by the blue threads of rivers in some seasons. And there's more to the global waterscape than meets the cartographer's eye. Rivers occasionally go underground, flowing unseen in channels eroded right through the heart of soluble stone. There are rivers running under glaciers, too. There are even rivers flowing in the sea. (So-called "turbidity currents," undersea rivers of muddy water, are thought to have carved many of the deep canyons along the margins of the world's continents.) In any case, the ubiquity of rivers is easily explained. The essential ingredient water is found everywhere on earth, though not always in liquid form. The other essential, gravity, is inescapable.
Given the commonalities of water and gravity, then, what serves to distinguish one river from another? Here's a short list:
- Climate How much precipitation falls, where it falls, and when
- Discharge How much of this precipitation is available right now
- Topography Water flows downhill, right?
- Bedrock Some beds are harder than others
- Soil type Some soils are impervious; some aren't
- Vegetation Plants are thirsty
- Beaver activity The world's first hydraulic engineers
- Human activity We may be late starters, but we're keen
OK. Let's tell
A Tale of Two Rivers
Take the rivers of my youth. One flows out of the Green Mountains of Vermont and then cuts across the westernmost ramparts of the Taconic Range. The other gets its start farther to the west and north, in New York's Adirondacks. North Country winters are (mostly) colder and longer than those of southern Vermont; the summers, cooler and shorter. More snow falls in the north in winter, and it lingers longer. Summer rains are sporadic, but when they fall, they're often heavy. The upshot? My Adirondack river is a flashy stream, swollen with snowmelt-fed torrents in April but apart from the days following summer storms dropping too fast and too far to maintain a boatable flow through the warmer months. The river where I spent my earliest years, on the other hand, can float a boat in all seasons. Mountain springs and groundwater keep the discharge up even in droughts.
The landscapes through which these rivers flow also differ. The Adirondack Mountains are blocky, irregular, and deeply incised. The valleys are steep-sided and straight, but prone to abrupt changes of direction. Bedrock lies near the surface, under a thin mantle of acidulated soil. Farms are few. Forests of cedar, spruce, and pine stretch for miles and stain the surface waters brown. By contrast, the Green Mountains (and the neighboring Taconic hills) possess a softer contour. Secondary and tertiary streams course down the flanks of broad ridges. These, in turn, separate wide valleys, where the bedrock lies buried far beneath a mantle of unconsolidated gravels, sands, and clays. Soils are deep and well developed. Farms are many and prosperous. Except on the steepest slopes, woodlands are fragmented and mostly deciduous.
All these differences are reflected in the distinctive characters of my two rivers. Yet the rivers have much in common, too. Each is an active principle, shaping the land that in turn will shape it: toppling trees, eroding banks, building 'bars. Given time, each has the power to literally move mountains. Moreover, while my Adirondack river is by far the more impressive in full spate, once you step back and view it from a distance it exhibits no more turbulence than its gentler Taconic cousin. A paradox? Not at all. The dynamics of moving water are independent of scale. A drainage ditch and a wild river are as alike as sisters. Want proof? Take photos of turbulent flow in both, under similar lighting conditions (black-and-white film is best). Zoom in and out to get as broad a sample as possible. Now crop away any trees, outsized bubbles, or other obvious indications of scale, print all the photos, and place them on a table before a friend. Invite him to identify which is which which photos show a drainage ditch roiled by heavy rain and which show the rapids of wild river. But don't hold your breath. Your friend isn't likely to do any better with his eyes open than he would with his eyes closed. That's what's meant by self-similarity over changes in scale, and it brings all flowing waters together into one family.
We'll return to this topic later. In the meantime why not reflect on the rivers you know best? See if you can identify the circumstances that set each apart from all the others. And give some thought to what unites them all, as well.