How to read a river: Riffles, runs, and pools

Inside this lesson:

Structural features
River behaviors
Biological elements
Riffles, runs, and pools
Riffles
Runs
Pools
How riffles, runs, and pools happen
Summing up

In our Intro to Fly Fishing class, the next level down from Watersheds in our Powers of 10 journey is to the levels of rivers and their features. One of the first activities we do is draw a river on the whiteboard.

It's simple river, to start. Two meandering banks, and an arrow indicating current direction. And then, we ask around for folks to call out what goes into it. As they do, we locate and place these "features" (crude icons and poor attempts at drawing).

It's not a trick question, although it can take a few minutes for everyone to warm up. Intuitively, we know a lot about what we find in rivers. There's a lot of different things—living and not—you'll find in a river.

Rivers contain:

• Banks and boundaries
• Rocks (of all sizes, from sand to boulders)
• Logs and woody debris
• Sediment and decomposed plant material
• Living plants (grasses, algae, moss, trees)
• Living creatures (insects, fish, birds, otters, sometimes humans!)
• Islands and rapids
• Eddies and currents
• Dams and other human-made constraints
• And much, much more

We could carve all these things up into three, probably:

• Structural features
• River behaviors
• Biological elements