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Learning the Language of Rivers II: The Basics

The views expressed are those of the author and are not necessarily those of Scientific American.


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This post was originally published at En Tequila Es Verdad. For those who haven’t yet seen it – enjoy!

***

The Marys River at Avery Park had me staring in incomprehension like a kid on the first day of a foreign language class. You know how that is: the teacher’s off babbling in said foreign language at Warp 9, and you begin to wonder why you ever decided to take a foreign language in the first place. And you doubt you’ll learn so much as a word, because none of it makes sense – your teacher might as well be speaking Greek, even though you signed up for French. Or was it Spanish? It all sounds alike when you don’t understand a word.

But you’re here. You signed up for this shit. All you can do is try not to look like a dribbling fool while you strain your ears for a single familiar word.

Marys River at Avery Park. View is upriver.

Marys River at Avery Park. View is upriver.

We’d come down for a quick gallivant along the river. There were some great fluvial features here, Lockwood said. And he’d say things like, “This is the Marys River,” and I would say things like, “Oh. Ah.” And while he said things about it that I didn’t in the least understand, I kicked around its banks and thought it pretty typical. I’ve started to become used to the Pacific Northwest’s idea of what a river is, and this is representative of the semi-domesticated type located on our basin floors. It’s somewhat narrow (by PNW standards – by Arizona standards, this is practically the Amazon). It’s cut down into the soft sediments and made itself a nice bank upon which trees have decided to grow in, shall we say, abundance. It will sometimes ignore those banks in order to go visit the surrounding areas, but not after a dry spell lasting over three months. It’s calm enough to reflect the trees. It curves gently here and there.

Marys River at Avery Park, looking downriver.

Marys River at Avery Park, looking downriver.

Just here, it’s hard to tell where civilization ends and normal river processes begin. We’ve got a little waterfall, pretty typical of PNW rivers where they’ve either piled up some rocks or encountered some rocks they haven’t been able to wear down yet, but this looks like people put this one there to modify how the river flows.

Mini-waterfall on the Marys River. This looks human-built.

Mini-waterfall on the Marys River. This looks human-built.

I mean, there’s no call for it. Not naturally. The river isn’t flowing over bedrock here – I believe it’s alluvium for a quite a ways down. It’s got quite a collection of small rounded cobbles built up -

River gravels. You can see under the water that it’s mostly just pebbles and cobbles with very little sediment. The dry bank is a different story.

River gravels. You can see under the water that it’s mostly just pebbles and cobbles with very little sediment. The dry bank is a different story.

- but it does not seem keen to collect angular rocks that look like your basic riprap. I may be ignorant about rivers, but I know enough to understand that down here on this flat valley floor, where the river meanders in classic lazy meandering fashion, you do not end up with big, water-transported, angular chunks of rock. They’d have had their corners knocked off at the very least, and it would have been one fuck of a flood that could’ve brought rocks down the distance they must have been transported, not to mention it’s highly doubtful that the river would then have deposited them in a fussy straight line. So that was easy to dismiss as human modification. But what about this bank?

Marys River bank, showing cobbles embedded in muddy matrix.

Marys River bank, showing cobbles embedded in muddy matrix.

For some reason, this isn’t computing for me. It feels and looks for all the world like some kind of concrete, like people at one point decided there needed to be a nice concrete slab poured into the bank, and they used coarse gravels to mix it. But most people wouldn’t use mud instead of cement, and hard as the matrix is, it’s distinctly mud-like in color and texture.

Odd bank, foot for scale. You can see where the river’s plucked bits out.

Odd bank, foot for scale. You can see where the river’s plucked bits out.

I am, I realized, so ignorant of rivers that I can’t make rapid sense of this. I’ve not seen a river build a bank like this. But a clay-rich silt deposited over the cobbles carried when the river has a more vigorous flow might do this, amirite? The glacial outwash that infests our lowlands forms a near-conglomerate like this: river gravels stuck in a thick, clay-rich matrix that is dreadfully hard when it dries. So this stuff is weird, but it’s not out of bounds.

On the way back up, I stopped for a look at the bank, and was intrigued by the rich red color of the soil here. It looks like weathered basalt, but obviously isn’t just that – it’s got river gravel in.

Sediments in the river bank. Silver dollar for scale.

Sediments in the river bank. Silver dollar for scale.

So the river’s obviously bounded over its banks, and enthusiastically deposited stuff, and some of that stuff is rather orange. I know too little about fluvial soils to know if that’s because the Marys River drains an area rich in weathered basalt soils, or if it’s due to something else.

So that made me itchy. So did this not-knowing where the Marys River came from, or where it was going. Did it come down from Marys Peak? Somewhere else? How messed about by humans was it?

There was a clue farther up.

Community Garden. This is a cut-off meander. The river’s trying to tell us something…

Community Garden. This is a cut-off meander. The river’s trying to tell us something…

Right. A cut-off meander. Well, I don’t speak the language of rivers at all fluently, but this is one of those phrases I know, like, “Hello, the bellboy has taken my pants.” This river, at least in the past, turned hither and thither with abandon. Judging from the fact that so much of it within our sight on the bank had been curvaceous, it seemed like it at least hadn’t been straightened by people. And it had been free enough to cut itself a new path.

A look at the map confirms: this river’s been hemmed a bit by humanity, but it hasn’t been tightly controlled.


View Larger Map

Down here, we’re 39 miles in to its 40 mile course. It’s descended from 650 feet to just a bit over 200 feet above sea level. It’s drained 310 square miles of mountain and valley, collected its tributaries’ contributions, and had a look round the valley. It’s passed through some quite interesting geology (pdf). It’s dumped an appreciable portion of its sediment, certainly enough to change its course as it aggraded its channel here and there. And in just one mile, it’s going to join up with the Willamette River. All done, chief.

And it’s still got quite a lot to teach me, because up till now, it’s only been covering “Hello, how are you, I am fine, my aunt’s dog is sick.” But it’s about to grab me by the lapels and say, “This is where it gets complicated, kid. I’m about to make your tongue move in ways it hasn’t moved since you were an infant.”

Dana Hunter About the Author: Dana Hunter is a science blogger, SF writer, and geology addict whose home away from SciAm is En Tequila Es Verdad. Follow her on Twitter: @dhunterauthor. Follow on Twitter @dhunterauthor.

The views expressed are those of the author and are not necessarily those of Scientific American.





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