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Learning the Language of Rivers II: The Basics

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.

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.

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.

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.

– 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.

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.

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.

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…

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.”

Comments

  1. geocatherder says

    Mmmm. A sand grain deposited here, a cobble there, another one lifted from a cut bank over there… and it all adds up to make one helluva story.

    Dana, have you ever seen a cross-cut of an old stream channel? If not, one of your PacNW geology peeps must know of one somewhere. They’re fascinating.

    • lockwooddewitt says

      That’s a good point- they really are! But I can’t think of a good one off the top of my head. There’s some nice ones along the Smith River in N Ca, where we’re hoping to get next year, but they’re very course, and not accessible for careful inspection. I’ll have to look through some photos from last summer’s southern/central OR expedition- we saw a couple of cuts that might have some okay (not great) examples and exposures.

    • Eskered says

      Best cross-cut stream channels I’ve seen out here were at Lloyd’s Sand and Gravel Pit in Milton, WA. It is just east of I-5, you can see it in the distance as you turn north out of Fife on I-5. When I last saw it about 6 or 7 years ago, it had south- and west-facing vertical cut slopes into about 50 feet of Advance Outwash sands, deposited by meltwater streams in front of the advancing Vashon Glacier.It was loaded with meadering stream channels, and you could see a series of old channel banks as they shifted one way or the other. It has about a 15 to 20-foot-thick cap of Vashon Till over it. They might let you in to take a peek if you ask.

  2. lockwooddewitt says

    You might be able to see that meander cutoff a bit better in Flash Earth. http://www.flashearth.com/?lat=44.551553&lon=-123.273044&z=18.5&r=0&src=msl But what really brings is out is the terrace breaks seen from ground level- and I’m kind of disappointed with the shots I got there. But to clarify, the loop goes off to the right in Dana’s photo, and you can kind of see the terrace break at the other end of the field. We’re standing at the base of the slope of the other side, from the perspective shown in the above picture.

  3. Mag says

    Been reading off and on, but didn’t realize you were a neighbor. Howdy!

    If you wanna see crazy river/stream/creek history…take a gander at a lot of the farmer’s fields in the area. You can totally see where it looks like Muddy creek used to cut through one of our fields at Stahlbush, and how the Willamette would love to cut through our dike and into Knife River’s old mining pond.

  4. stevegough says

    From a guy who’s analyzed hundreds of miles of stream channels (I’m getting so old), many of them in human-impacted places like this, here goes: The line of rocks is definitely human-placed; and the angular rocks may have some from nearby rock that hasn’t been water-worked. Also in actively-incising/migrating channels in urban areas we see angular bank stuff eroded into streams. The fines/gravel mix is from either a damming episode (either logjam or anthropogenic), or was mixed and placed by a big yellow machine. Probably the cut-off was machine-made, too, and may be related. The historic aerials will tell you an interesting story I’ll bet. And at one/both ends of that dry channel you will find telltale berms/levees built to keep the channel out of it. Hope I get to look at one of these with you some day! Great post.