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Weekly Roundup – Geomorphology Lesson Daily – April 3

Here’s a look back at our first week of #GeomorphologyLessonDaily. We’re compiling these lessons with high schoolers in mind, but the content can be used for other levels as well.

Stream Channelization Video

Monday

In this video, we take a lovely naturally meandering river and straighten part of it. Consequences follow. 😮

In this case the channel length between two points is more than halved, so slope would increase by a factor of 2+.

Note the relative stability of the system before channelization, in which a small amount of sediment is moving through the reach, but there is little bank erosion and by one definition—sediment in = sediment out—the system is very stable. A moving circle and the words “uniform bedload transport” illustrate this.

After the channelization note bank failures both up and downstream, and that the channel slowly reestablishes a meandering form so that its overall length is about the same as before the channelization. Graphics show how bedload transport greatly increases due to incision and bank erosion upstream of and within the reach.

During the remeandering process, note that there is a net export of sediment—you can see this by visually comparing sediment movement into the reach versus that out of it.

Fluvial Geomorphology & River Conservation Videos

Tuesday

Check out our recent blog post to learn about rivers, featuring videos made by The Wild Trout Trust, with descriptions by our own Steve Grimmer!

River Lessons — Videos by Wild Trout Trust

Logjam Formation Video

Wednesday

This video shows how logjams tend to form where straight, channelized reaches transition to meandering planform. This typically occurs when channelized reaches join unchannelized ones.

In this example, we see small simulated trees and logs flow quickly down a narrow, relatively deep straightened reach into a meandering channel. Graphics show the cross sections at a transect in each reach.

The wood is effectively moved through the deeper, faster-flowing straight reach, but tends to hang up in the meandering reach, which is wider and shallower.

Wood also hangs up on the banks as the channel bends. As some wood is trapped, other wood piles up on it.

And it’s not your imagination; this clips is somewhat marred by occasional vibration of the camera mount.

River Deltas in the Arctic

Thursday

“Ice cover, a distinctive characteristic of Arctic deltas, tends to preserve uneven arrays of channels by freezing small channels in place and preventing them from filling with sediment. At the same time, ice melts fastest over larger channels while it still plugs the small ones. Large channels therefore carry the bulk of spring floodwater, which may carve them even deeper and wider.”

Learn more in the article here.

 

screenshot of our twitter post

Mixing Art & Science

Friday

Learn about an artist’s scientific approach to plastic pollution on beaches.

By Freija Mendrik on the art of Dan Lewis.

“Each beach clean is different from the weather to what I find. Almost all of my flat lay artwork, shows the microplastics from one single beach clean -revealing the variety of waste right there on a particular day. The work develops naturally as I arrange the pieces; in life and in my experience in many parts of education as a whole, we as students and as practising professionals tend not to trust what we make and are encouraged to avoid risk. Getting back in touch with the playful, experimental way of making is vital to me and essential to the variety in my work. I am planning larger single coloured pieces of work this year with more complicated patterns. New learning often comes when making an artwork with any medium or material, similar to science experiments – we can hypothesise what may happen, but until we test our ideas, we won’t know.”

See Dan’s art and read more about it here.

 

screenshot of our twitter post