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Why rivers meander

Have you ever wondered why rivers in their lower courses — in the plains — meander? This video is a fantastic primer for the intercourse of land and river.

This mid 20th century map traces the course of the Mississippi as it floods its plains, silts, up, carves new channels, makes ox-bow lakes, all the while meandering at will through the years. (Mississippi River Meander Belt: Cape Giradeau, MO–Donaldsonville, LA,” from Geological Investigation of the Alluvial Valley of the Lower Mississippi River, by Harold N. Fisk, 1944).

mississippi_map_1999265

Now, welcome to the anthropocene world, where we pull and push and straighten and alter a course, trying hard …

… To tame a river

In this excellent explainer about What We’ve Done To The Mississippi, Alexis C. Madrigal runs us through the infinite ways humans attempt to control nature, and still to some extent come a cropper. The river still floods its plains (see this fantastic photo essay in The Atlantic on the 2011 floods), cresting record heights and devastating parts of Mississippi and Louisiana.

On the same topic, do not miss John McPhee’s essay in the New Yorker on Atchafalaya, which is also in his book, Control of Nature.

The attempt at taming of the Mississippi has also come with devastating effects on the ecology and economics that depend on natural systems. When you straighten rivers and build levees, when you remove the little nooks and crannies along river banks and interrupt flows with weirs and dams, you stop transport. Transport of sediment and the movement of creatures. Fish swimming upstream to spawn, eels swimming to the brine to spawn. Migrations of shrimp. The deposition of silt that makes deltas, that keeps building up landmasses so that it may not all erode under the incessant assault of the ocean and, now, rising seas.

Where have the shrimp gone?

In Life On The Mississippi: Tale Of The Lost River Shrimp, Paul Greenberg lays out what we have lost in order to gain control over nature.

It turned out that in pre-colonial times the shrimp traveled all the way north into the upper reaches of the Mississippi’s main eastern tributary, the Ohio River, and back again – a 2,000-mile round trip. It was a journey more amazing than similarly epic migrators like salmon. For whereas adult salmon may have an equally long journey to their upstream spawning sites, it is the quarter-inch juvenile shrimp that swim and crawl 1,000 miles upstream against the strong currents of the Mississippi.

Hartfield turned to historical fishing records and found that not only were river shrimp present in the days of the early colonization of the river, they were a major source of food. In fact they were the shrimp that poor French Acadians found when they migrated from Canada. In 1898, 200,000 pounds of river shrimp were taken by the poorly documented fishery of the Mississippi River and we can assume many more were caught and never reported. Albert “Rusty” Gaudé III in the Louisiana Sea Grant office confirmed this. “I ran the numbers,” Gaudé told me, “and that catch was worth millions of dollars not in today’s dollars but in their money.”

But out on the river, as we hauled up trap after trap, we found only one or two shrimp per trap. Where had they all gone? I asked.

….

The natural way of the Mississippi (and indeed all rivers) is to meander and flood. The turning of the earth bends a river askew as it makes its way downhill. Gravity draws the river back down its original path but momentum causes it to overshoot its gravitational mark and bend again, this time in the other direction. The result is a curvaceous affair wending from the top of the continent in Minnesota down to the bottom in southern Louisiana. A river like that has a wide floodplain rich in nutrients that drop out and fertilize the flora and in turn generate long chains of life from algae up to large carnivores.

Indeed, though the generally accepted Indian meaning of the name Mississippi is “father of waters,” some etymologists say the name stems from the language of the Outouba tribe in which the word Missi meant “everywhere” and sipy meant “river.” Mississippi – literally “the river that is everywhere.” This describes the river as it is really supposed to work – a floodplain dozens to hundreds of miles wide, that gathers water draining from the Rockies to the Appalachians. A sloppy mess where water does what it wants to do.

But not only does water do what it wants to do, it does what fish and shrimp want it to do. The Mississippi once abounded with local fish. River shrimp, giant catfish, caviar-producing sturgeon, a carp-like creature called a buffalo fish – all supported a vibrant local fisheries economy.

But a river that is everywhere is hard to use toward profitable ends …

And so we straighten rivers so we can have profitable and shortened routes to the seas. Waterways. When, in fact, rivers are much more than that. And try as we might, the awesome power and force of water will try to regain, retain its innate nature.

In attempting to over-engineer it we invite disasters upon ourselves.