Removing Dams: The Good, the Bad, and the Messy

“Set the river free” is a cry heard more and more often. It started in New England, when old, unused water diversions and containment structures were removed, often for good reasons, from smaller streams. The goal was to let the stream or river return to as close to original as possible, or to prevent a dam failure and the subsequent floods and damage. If the thing doesn’t serve a purpose, and might even have become a hazard, why not take it out? And again, in some cases, it made good sense. In other cases people took sediment samples from behind the dam and said, “Hold up a second! We don’t want this in the river.” And so the dam stays for now.

However, there’s a difference between a little mill-dam or a small diversion on a stream in what has reverted to forest, and a good-sized power dam, or flood control structure. And you can’t just “rip it out and let the river heal.” Depending on the dam, the river, and what’s down stream, that can lead to disaster, at least for the very aquatic life that people are trying to save/reintroduce.

So, a quick primer on what happens behind the dam when the water flow is greatly slowed or stopped. A large puddle forms, growing into a pond or lake. If the river carries lots of sediment (silt, sand), then the heaviest of that begins to settle out into the bottom of the lake. As the lake fills, the weight on the ground increases, as does pressure on the dam and the sides of the lake. If excitement is going to happen, this is when the first signs appear (Teton Dam is the horrible warning). A little seepage is pretty common, and should be clear. If muddy water starts appearing on the wrong side of the dam, then Things Need to Be Done. If all goes as planned, a lake fills in behind the dam. Hydropower dams use the pressure of that water to turn turbines that generate electricity, so they are always releasing water, or do so intermittently to meet peak demand. Irrigation dams draw-down water levels in the dry season for farmers to use, then allow levels to rise again in the wet. Recreational dams hold water at all times, unless there is a compelling reason to release water (controlled flooding as opposed to uncontrolled “it ate the dam!!!” flooding. See Johnstown for the horrible warning.)

Over time, if the stream carries enough silt, the lake might just turn into a mudflat with a waterfall on one end. That is very, very rare, at least in the modern era. You can see it with ancient structures in Arabia and a few other places. Eventually the dam wears away and you have to look very carefully to see that a water control structure ever existed. Most modern US dams have a life-time of about a century or so before something needs to be done about the silt, it silt deposition is a problem. Something like Hoover Dam or Glen Canyon? Not such a problem.

So, let’s say you want to tear out a mill-dam on a rocky stream that never had much sediment. You do a core check of what’s behind the dam, find nothing toxic and no huge slugs of sediment, and decide to get rid of the structure. Some sludge and gunk will flow downstream, so ideally you allow a slow release and everything keeps going until the sediment reaches the sea (or the next lake downstream) and you have a nicely restored river. You are happy, the land owners are happy, and the fish are happy. Good deal.

However, let’s say you look at a dam downstream of an industrial area. It needs to go. So you take a core of the yards’-deep sediment behind the dam and Whhoooooooah Nellie! Arsenic, dyes, lead enough to rearm the Ottoman Empire, and a few other things have accumulated. Do you really want that going downstream and settling all over the stream? Probably not. The better thing to do is to lower the dam, allowing increased flow-through but still keeping that “stuff” penned up and out of circulation until someone decides they want to pay for the removal and remediation.

So, what if there’s been no, zip, nada industrial development in the area, ever. Your core comes out clean, but full of sticky, silty, sludge. The flow in the stream is not what it used to be, for a number of reasons. If you rip out the dam, it will take a very, very long time for that material to get through the stream. Most likely, the stream will aggrade, getting shallower and wider, leaving the sediment over the current bed. It can also cause the shallower water to be warmer for a while, until the balance starts to return after more sediment is carried downstream. If you have really good trout fishing downstream, this is probably not the scenario you want. Now you start talking about dredging out the stuff, taking it somewhere else, and then opening the dam after the water settles again. $$$,$$$,$$$.00 can be involved.

So, OK, what if we just rip out Hoover, or Grand Coulee? Well, first, where is that electricity going to come from? Nuclear is the only close replacement, because wind and solar are not going to work. Second, that will be an enormous slug of very, very cold water racing down the Colorado River valley and taking a lot of stuff with it. Like downstream dams and diversions. Like any water-supply intakes. The fish will be in for a surprise with that temp, although the modern Colorado is far colder than it once was. And eventually the sediment will start to move, slowly, and you will get back to closer to the old Colorado, brown, wild or sluggish, and meandering. If you get/got drinking water from downstream of Hoover, well, buy a lot of filters and plan on changing them regularly. And get ready for floods, as the bed, once scoured, starts to rebuild with that sediment.

Did I mention floods? Annual or semi-annual floods will return. Any valuable infrastructure will have to be relocated, or turned sacrificial. You’re going to lose habitat for some creatures and gain it for others. Given the sediment that’s built up behind the dams of the 1910s-1950s, anything that needs a rocky bed with well-oxygenated water might have difficulty for a while, depending on how quickly the sediment is redistributed and filtered out as the balance in the stream resumes.

Note: All these are controlled removals. Nightmare fuel is if one of the big dams on the Colorado goes all at once, because then the downstream dams will likely go as well. The Colorado will reach the sea again, perhaps by a different route. Or it might refill the Salton Sea and a few other areas, then head out via LA or even double back and then go out to Baja. The loss of life would be tremendous, the loss of infrastructure eve more so.

So dam removal can be done, and done right. However, “rewilding the Columbia and the Colorado!” is probably an undertaking best left to fiction writers for now. Until nuclear reactors become far more common, and we know a lot more about what’s behind those structures and how to release the contents slowly, we could do far more harm to the environment than we ever did by building the dam.

Playa Lake 101

A re-post from 2018.

My long-time readers will recall that last year I was following a local playa lake over the course of the seasons. I’m still doing that, but it has been so dry that the view has not really changed, at least from the place where I take pictures. Unless you really know what to look for, all you see is swaths of brown stuff with slightly enlarging or contracting patches of green stuff. Not really gripping blog fodder.

So I thought I’d go back to what a playa is, on the off-chance we get more precipitation and water actually, you know, shows up in the lakebed. Continue reading

“Hunting or Fleeing”

That was the heading on a side-bar in an archaeogenetics book I’m reading. The question concerned modern humans’ adaptations that enabled us to stand upright and walk preferentially on our hind legs. Me being me, and having read about hunting big game, my thought was “the difference is . . . 2.3 seconds. Or less, if it is a Cape Buffalo.”

I AM smiling. Creative Commons Fair Use. Original source: https://cannundrum.blogspot.com/2014/07/cape-buffalo.html

Even the dedicated plant eaters on the African continent will track you down and turn you into pulp if you earn their ire. The Cape Buffalo . . . was born with an attitude that only gets worse as they age. Cape Buffalo spend their free time premeditating murder, or at least mayhem. Slow hunters? “Target acquired, gore, hook, and trample at will.” It would not surprise me at all if some naturalist discovers a secret Cape Buffalo score-board, where the buffalo list the number of humans et al that they’ve removed from the gene pool.

I suspect ancestral humans spent a goodly amount of their days avoiding wildlife as well as stalking and killing it. It is only in very recent history, in a few specialized environments, that humans have become the only apex predator. I’ve been out in the not-so-wilds of the US and have been stalked. Once it was by a young bobcat. Once . . . I don’t know, but I didn’t linger, either. Mountain Lions were not supposed to be in that area. Alas, mountain lions don’t read press releases or Fish and Wildlife monthly bulletins. I’ve been chased by a pack of feral dogs once, and I can attest that I was no longer at the top of that food chain. (I also discovered I could climb a cliff like a pro when truly inspired. I’d just as soon avoid that inspiration, thankyouverymuch!)

Heck, when I was in grade school and on a Civil War battlefields trip with my parents and Sib, we found a large warning at Manassas/ Bull Run Battlefield. A doe had treed a hunter. She proved to be rabid (!) and the park rangers were telling everyone to stay the heck away from the deer, and to back away slowly, then quickly, if we saw one by daylight. Yes, Faleen, Bambi’s lady friend, had tried to kill a hunter.

The difference between hunting and fleeing? A couple of seconds, especially if the bow-string snaps, or the spear just makes the critter angry. Imagine our intrepid paleohunters sneaking up on a Large Beast. One eases to his feet, aims, and throws.

Thunk. “Roooaaaarrrrr!” Thud, thud, THUD!

“Um, Thag, I think you missed the kill spot.”

Natural History Writing

A good natural history book is a joy to read. They seem to be growing scarcer, alas, although it might just be that there are so many books out these days that winnowing “natural history” from “environmental dirge” from “pop-science” from “local writer writing about local birds” has grown far more difficult. But when I find a good natural history, it is such a treasure.

What is natural history? I know it when I read it. OK, beyond that, it is a study of a place over time, one that looks at everything from the dirt and rocks to the birds, plants, waters, land-use, and weather of a generally small bit of of the world. When you finish reading, you know the critters, flowers, trees, grasses, soils, and story of the land – sort of a biography of place, with a dollop of science. The first of these that is fairly well known in English is Gilbert White’s Natural History of Selborne. Selborne was the parish where White was minister for many years. The book was published in 1789, and is still in print. White described the place through the seasons, what grew there and why, and so on. Pliney and other ancient and Renaissance writers had done descriptions of places and critters, but no one had written a popular study of one small corner of the world.

White inspired a lot of other writers, some talented amateurs, some professionals, some a little of both. Aldo Leopold was a forest ranger with a gift for writing, and his Sand County Almanac and other essay collections are magnificent depictions of places, and meditations on “nature” and “Wilderness” and what those ideas mean for people and critters.

So, what’s the difference between environmental history (my bailiwick) and natural history? Environmental history is more academic, meaning it has all the things that are required of academic writing (footnotes/endnotes, historiography, formal introduction and conclusion with certain elements in them). Environmental history often includes a lot about people, government policies, laws and how they were applied (or were not), corporate history, you know, paperwork stuff. And they tend to cover more ground. A natural history of Cheyenne Bottoms in Kansas, for example, only talks about that particular place. It doesn’t go into discussions of federal and state wetland policies and how they changed over time, except as they related directly to the wetland, and then only one chapter at the end of the work. Instead, it starts with the geology, then the mud, the cattails and other things that root in the mud, the fish and bugs and amphibians, and works up to the raptors and other birds that live in and around the wetland.

I’ve tried my hand at writing a few natural history type things. I’m not good enough, and I don’t know enough to do a good job. Natural Histories are love songs. Environmental histories are ballads.

Book Review: Super Volcanoes

Andrews, Robin George. Super Volcanoes: What they Reveal about Earth and the Worlds Beyond. (New York: W. W. Norton, 2022) Kindle Edition

I’d hoped that this might be a book about supervolcanoes, the giganormous ones like Yellowstone and Toba. No, it is about how cool volcanoes can be, and about volcanic activity on Earth, the moon, Mars, Venus, and some of the moons of Saturn and Jupiter. It’s a very well-written, intriguing book, and you get the sense that the author is sort of geeking-out over all the cool rocks and ice and really strange things that volcanoes get up to.

Andrews is a PhD in geology who works as a science reporter. The book is a little breezy at times, as I’ve come to expect from “reporter does science.” However, the geology is sound, and once you get past the “oh my gosh, I love rocks!!!!!”, it’s a fascinating work of popular volcanology.

He begins with Yellowstone, and why the hype is just that. He does indulge in a bit of “OK, so if this does blow, how badly will it effect North America.” As badly as you’d think, even if the eruption is weaker than previous (as seems to be the pattern when continental crust moves over a hotspot). Then he considers other well-known mountains before moving to some truly outré mountains in Africa. I suspect African volcanoes are pretty much mysteries for most people, aside perhaps from Kilimanjaro, and perhaps those in Rwanda that have erupted within the past five years. East Africa has a marge number of active peaks, some of which possess the oddest chemistry terrestrial volcanoes this far are known to have. Part of the story is “how can volcanologists and locals work together?” and part is “crazy things people will do to get samples.” Ingenuity, desperation, and a low budget can work wonders. Lava that’s not exactly lava, lava that’s too cool to be lava (but that will still kill you), chemical stews that make even bacteria think twice . . . These mountains and rifts are not always friendly.

From Africa and then Hawaii, our intrepid reporter turns to undersea volcanoes and the black-smoker thermal vents. I felt a bit of a warped grin forming when he described how rarely eruptions undersea are recorded and observed by geologists in real time. This was, oh, three days after Tonga went dark under volcanic ash.

Lunar volcanoes, Martian mounts, Venusian vents, and things hanging out around Saturn, Jupiter, and parts beyond wrap up the book. No, this isn’t your usual geology book.

The end-notes are quite good, and the “climate change delenda est!” passages are generally short and skip-able. Something about how much CO2 volcanoes burp into the air compared to everything that humans do, and so on. No, we won’t become Venus because of burning coal and oil.

I recommend this book for people interested in more than just “This is a volcano. Volcanoes are mountains that make lava” and want a general, wide-ranging look at the topic. Andrews assumes that you have a basic understanding of geology, which I suspect most if not all of my readers do. He doesn’t write down, but he doesn’t go sailing over your head, either.* It’s a fun read for the rock buff, or people like Game Masters looking for evil new things to throw at their players (carbonate volcano!)

*Unlike a lecture on the chemical crystallography of the magmas of Kilauea and Mauna Loa and Mauna Kea that I lost track during and never caught back up. The conclusions were fascinating, but oooooh, then chemistry to get there!

FTC Note: I purchased this book with my own money for my own use, and received no compensation from either the author or the publisher for this review.

Interstate Water Treaties, or “Here We Go Again”

Nebraska is invoking a 1923 treaty with Colorado to build a canal and outmaneuver Colorado on the South Platte River. It’s been a while since an interstate water fight made the news, and I can hear water lawyers on all sides organizing papers and smiling at the prospect of a fight. After all, whisky is for drinking but water’s for fighting over.

My first thought when I heard the news was to grin a little, because Colorado has some water policies that make me roll my eyes, especially policies pertaining to the South Platte River. Among other things, the state banned the collection of rainwater runoff by private individuals (no cistern at the end of your downspout) on the grounds that if too many people did it too well, it would affect in-stream flow on the South Platte and violate the river compact. Translated into normal English, if people collected the rainwater, there wouldn’t be enough run-off into the river. The quantity of water would drop below the minimum required by law. That minimum has to go to Nebraska, or else, unless there is a drought or other 100% non-man-made event in progress. Even water lawyers can’t make rain where rain doesn’t want to fall.

An interstate compact is a treaty. It must be ratified by the US Senate, just like any other treaty. Most of the interstate compacts I know of are about water, dividing up the flow of rivers, or discussing quality. The goal of a river compact is to keep, oh, Texas from sending the Guard into NM and doing in a dam, or suing for $$$ in lost income and property if the upstream state dries up the river. The Colorado River (of the West) is probably the most famous of these compacts, and one of the most litigated streams in interstate water law. The Pecos River and Rio Grande are not far behind, then the South Platte, and some rivers in Wyoming. https://ballotpedia.org/Chart_of_interstate_compacts A quick skim of the list shows that most of the compacts involving rivers from west of the 100th Meridian are about in-stream flow, and protecting downstream users from upstream excess usage. Mexico is also a party to some Compacts, notably on the Rio Grande and Colorado.

The first official compacts over in-stream flow date to the 1920s, when irrigation got better and litigation more common. What had been local (except in NM and CO) became a state matter. It’s one thing for Garden City, KS to complain about a lack of water in the Arkansas River. It’s another for Kansas to sue Colorado in federal court. Also, the surge in dam and irrigation-project construction in the 1910s and 1920s led to a surge in lawsuits. Thus the compacts. Some are just quantity, others are quality as well as quantity.

As long as people use water from rivers, or use groundwater that affects rivers, others will watch with beady eyes. “I’d rather be at the head of a ditch with a shovel than at the end of the ditch with a decree.” “Whisky’s for drinking, water’s for fighting over.” “The boy at the spring controls the stream.” [Ein Knabe am Quelle controliert den Fluß.]

It’s been a while since an interstate water compact bobbed up in court. The last time, it was TX and OK vs the US government over control of the banks of the Red River. There’s nothing like the Feds sticking an oar into things to get the states to drop other fights. Now it’s Nebraska making waves, and Colorado backpedaling, at least for the moment.

I encourage you to read the compact for yourself. River compacts are some of the clearest of legal documents, not that it prevents lawyers from muddying the waters. The University of Colorado law school has a water law specialty. Other states have something similar, at least those where “prior appropriation” is the rule for water apportionment.

Book Review: Garden Variety

Hoenig, John. Garden Variety: The American Tomato From Corporate to Heirloom. (New York: Columbia University Press, 2018) Hardcover.

We all know that there are only two things that money cannot buy, per country music. Those are true love and homegrown tomatoes. Most of us have probably grumbled about the visually perfect and rather bland super-‘mater that is found in grocery stores in January, and many of us have sighed and sweated over trying to raise our own tomatoes in pots, or in gardens. And then felt overwhelmed by the produce overload that is known as August-September (in much of the US). Tomatoes are argued over, debated, immortalized in song, have a folk history, and serve as a powerful symbol of the problems of mass-grown corporate agricultural produce. But what if that story is a lot more complicated that most activists think? Enter John Hoenig and his fun book, Garden Variety.

Hoenig starts about 200 years ago, looking at the slow rise in popularity of tomatoes, and the problem of preserving them. You can’t easily dry, smoke, salt, or otherwise store tomatoes. Potatoes, corn [maize], turnips, squash, cabbage, beans, all can be easily kept for the long duration of winter, but tomatoes were a seasonal luxury until canning came along. Ketchups of mushrooms, then tomatoes, and sauces came first because of the limits of technology. Those limits also led to the creation of lots of regional canneries, each using local produce and serving a limited area. In those places where immigrants and others introduced new diets, like the Italians in the late 1800s, tomatoes became a luxury, then a necessity. To have the first tomato of the season brought a lot of money to farmers, and so cold-frame-grown tomatoes appeared, or tomatoes shipped by rail. However, most tomatoes ended up in cans, either at home or through the local cannery.

WWI and especially the Great Depression and WWII led to the explosion of both canned tomato products and the super-cannery. Standardized foods, like canned diced tomatoes, tomato paste, Ro-Tel™ tomatoes-n-peppers, and canned meals grew in popularity. The wars absorbed almost all the tomato products that Heinz and others made, forcing gardeners to can at home. With the shift in the economy and changing leisure-time interests, home canning faded for a while. That shift also led to the end of the bracero and other farm-labor programs. This is where the “industrial tomato” arose, when labor shortages in the 1960s forced growers to finally take interest in a mechanical harvester. Said harvester needed sturdier tomatoes, leading to the modern industrial hybrids.

Most histories of food in the US turn here, following the rise in mass-consumption and the “blanding” of the American diet as corporations came to dominate agri-business. However, Hoenig takes a different track, and points out how a combination of “back-to-the-land,” “gourmet,” and “traditionalists,” led to the resurgence in farmers’ markets and heirloom local tomatoes. Yes, most packaged produce still comes from big farms and corporations. However, the local tomato didn’t wither on the vine, and in fact old-breed varieties grew in popularity, as did farmers’ markets and Community Supported Agriculture (CSA). This complicates the story of “corporate food.”

The book is shorter than it seems, because of the extensive end-notes and bibliography. It is not academic, for all that it is written as an academic monograph. Hoenig aims the work at interested readers, people who might know a little about farm history, or gardening, or food history, and who want to learn more. There are no bad guys, no super-heroes, unlike some books about farming and agri-business in the US. The story never strays from the tomato. I got the sense that Hoenig is not entirely comfortable with the giant corporations that dominate supermarket shelves, and the environmental problems associated with monocrop farming. Those topics are not his focus, however, and he steers clear of the shoals of polemic. I suspect a lot of us share his concerns, and are interested in buying local and supporting more variety in ag when we can.

I highly recommend this book for readers interested in the history of food in the US, in farming and mechanization, and in quirky histories about produce.

FTC Notice: I purchased this book with my own funds, and received no remuneration or consideration from either the author or publisher for this review.

“And the crooked straight, and the rough places plains . . .”

At least, that’s how I always understood it.* I mean, growing up on the Great Plains and High Plains, flatness is just part of life. Land tends to be flat, with a few lumpy exceptions, and those lumps are trying to become flat. So it’s easy for a child to look around and thing, “Yes, yes He did, and plains they are indeed.” Being in Hungary felt like being home, aside from the Bronze-Age burial mounds. Ditto northern Germany and Poland. They are flat, and green, and windswept. That’s a landform after my own heart (because I like to see weather before it hits me.)

Land erodes and tries to become one with sea-level, or to become a peneplain. One common understanding of a peneplain is that the peneplain is the lowest elevation and form that a basic surface can erode to at any given time. It is “at rest” and stable, at least until something changes (geologic uplift in the neighborhood, or sea-level change that leads to increased erosion by streams, which leads to surface erosion.) In theory, should tectonic processes ever end (the Earth cool enough that the plates stop moving and circulation in the mantle and Moho stop), everything will erode down into basic flatness. Unless someone repeals the Law of Gravity, that is. However, that’s a very, very long way in the future, so we are stuck with uplift and erosion for the time being.

Fair use from Fastwindtoaim.blogspot.com.

Geologists and rock-buffs generally don’t geek-out over plains. Giant plateaux, maybe, depending on your specialty. The Tibetan plateau is high and pretty cool (and getting higher in places). The Llano Estacado sprawls and is not as dramatic, unless you are in a four-cylinder car with a headwind trying to climb the escarpment from the west. Plains are, well, plain. Unrelieved topography, they may roll gently like a mild sea, up and down and up and down for miles and miles. Or they may look as flat as a pancake. Kansas, however, is flatter than a pancake, assuming an Ihop™ basic pancake scaled up to match the east-west width of Kansas. {Journal of Improbable Research, however for a rebuttal see also: Kansas Geologic Survey as cited here] The High Plains of Texas makes Nebraska and parts of the Dakotas seem positively lumpy, although the peneplain in Illinois is still used as the textbook example.

Plains tend to be places to farm, graze, or travel over en route to more interesting or sheltered locations. When Texas advertises for tourists, the Texas Plains Trail is well down the list of attractions compared to the mountains in the Trans-Pecos, the fishing in East Texas, the Gulf Coast beaches, or cultural stuff, or the Hill Country. Nebraska doesn’t brag about being mostly flat (or about being seen as being mostly flat. The Sandhills are not flat, I assure you.) Flat is boring, flat is dull, flat is easy. Anyone can build a road across flat terrain, unless it is a swamp full of pothole lakes like the eastern Dakotas, western Iowa, and parts of Minnesota and other states were. Flat does not drain, so you get bogs, sloughs/slews, seasonal marshes, or enormous swamps like the Great Dismal or the Pripet Marshes. Plains can be dry or moist, or seasonally moist. Water tends to puddle unless there is a well-developed drainage (see Illinois) in place.

Due to gravity, prominent landforms such as mountains erode, wearing away until the sediments reach a state of rest. That resting state can’t fall or roll any farther, and becomes a plain. The Great Plains of North America are full of sediment from the mountains east and west. So while Isaiah was a little off about “every valley will be exalted,” he was correct that “and every mountain be made low.” It just takes time, water and wind and gravity, and sometimes a little help from explosive eruptions.

*Isaiah 40: 4-5

Every valley shall be exalted, and every mountain and hill shall be made low: and the crooked shall be made straight, and the rough places plain:

And the glory of the Lord shall be revealed, and all flesh shall see it together: for the mouth of the Lord hath spoken it. (KJV)

Oxbows, Cut-offs, Meanders, and Snags

So, how do you lose an entire large-ish boat, that sinks intact, for a hundred years or so? Well, if the water is muddy enough, and the place is remote enough, you just don’t see it. Especially if that river likes to wander all over the place at whim, or at least at what to most people looks like whim. Welcome to the Mississippi and lower Missouri Rivers, two streams that snake more than the reptile house at the National Zoo.

What makes a river take a certain shape depends on a handful of elements. First is the geology under the river – is there room to move? Yes, over time the stream will cut a channel, but if the slope of the land is low, and the surface is flat, and the surface is also loose (lots of dirt, or sand, or small gravel), then the stream will tend to take on a series of S-curves, especially if the stream gets a decent amount of in-flow. Something like the Republican River in western and central Nebraska doesn’t get much inflow, so it tends to be straighter than similar streams east of the 40″ rainfall line. Glacial outflow streams carry lots and lots of gravel and smaller sediments, so they wander as well, even though they may be over bedrock (if you dig far enough). Even the Colorado River (western, not Texas) cut bends through very hard material, because it carried a lot of sediment that acted as an abrasive. It had room to move, until it cut that rather deep canyon.

Because of all the sediment, when the flow of water slows down, the sediment eventually settles out of the water and onto the bed. This builds up the bed, and if it happens long enough, the river moves to the path of least resistance. If the flow of the river rises and falls, as used to happen (still happens to an extent) with the Mississippi and Missouri, then the river also dumps “excess” energy by moving into an S-pattern. The bends shift location over time. This is why, after big floods, the riverboats on the Mississippi and Missouri had to be very wary of snags and changes in the river’s location. The flow of water that had carried small islands, entire trees, huge glops of dirt and sand, wasn’t there any more, so the river had less energy, and dumped the load. Now the boats got to find those lumps, and trees, and avoid them. You didn’t want to be the first boat up the stream after a big flood. Sort of like being the first rafting group down the Grand Canyon after a big storm or high water. Surprise!

DeSoto Bend in Nebraska is no longer a bend. It is fields around an ancient island. The river relocated. Depending on physics, weather, and inner perversity, a river may build up natural levees and terraces, like the levee that keeps the Garden District in New Orleans above many floods. That neighborhood was built on a natural rise, for good reason.

If the river moves far enough, the bend might get pinched off and an oxbow lake forms.

https://www.geocaching.com/geocache/GC2R70K_etobicoke-creek-meander-for-now Source of image used under Creative Commons Fair Use.

Over time, the oxbow may dry up. Unless you look at the soil from above, or study soil-type maps, you’d never know that there was once a river there. Fly over the Mississippi on a clear day in fall or winter, when the crops have been harvested, and you can see the ghosts in the fields, the long-gone bends and oxbows.

Fair use from: https://revision.co.zw/meanders/
Fair Use from: https://laurasriverfeatures.weebly.com/meanders.html

Rivers wander. People try to keep rivers from wandering. This means dredging a channel, or building levees to constrain the wandering. Dredging can speed up the river, meaning it erodes more, or starts snaking more downstream of the deeper channel, or eroding upstream, or “Yes.” Levees can work, until you end the levee and the river starts dumping sediment and snaking more. All these mean that floods will spread farther below the dredged area or levee, unless the river decides to dump lots of sediment on the dredged area. This is called agrading, “building up the bed” as opposed to degrading “down-cutting the bed.” If a river has to be channeled, ideally, there will be areas nearby that are left as flood-zones, so that the river can release the energy and sediment that it needs to lose. And so that floods will happen in anticipated areas, and downstream floods won’t be as bad.

The problem is, when the Mississippi and Missouri and other streams were channelized, we didn’t know what we didn’t know. As much as I’d love to see those rivers revert to their old ways, I don’t think people are willing to sacrifice the infrastructure and good farm ground that has been developed along the streams. It’s like, oh, the plan to reintroduce certain fish to the Rhine and revert it to what it was before 1800s. You’d have to dismantle so many buildings, factories, power-plants and other things, and then tolerate floods and erosion and deposition and the mouth of the Rhine moving around and no more (or far less) shipping, and . . .

Eventually, the river is going to win. Rivers do that. The Old River Control Structure on the Mississippi is going to “fail,” meaning the Mississippi will route around it and shift back to an earlier channel and outlet to the Gulf of Mexico. Eventually, levees on other rivers are going to be overtopped so badly that they can’t be patched for months, or more likely years. Physics is on the side of the river.

As one older Midwestern farmer put it, “The river always flooded. That’s what rivers do.”