HCC General Forum

A classic description of the physical forces that shape river meanders was published by Leopold Luna and W. B. Langbein in Scientific American magazine back in 1966. It is a pleasure to read, and it contains some wonderful illustrations. My personal favorite is an aerial photo of a 1965 train wreck, in which the still linked-up train was compressed into the same shape as a classic river meander after the locomotives were suddenly stopped by a collision. These two phenomena may not appear to be related at first glance, but Leopold and Langbein explain the connection. 

A thought experiment that was described by Albert Einstein in 1926 gives an interesting insight into the transport of sediments from the outside of one river bend to the inside of river bends farther downstream. He thought about the reason why tea leaves in a stirred cup would end up settling to the bottom, in the middle of the cup. The flow in the cup is kind of like that of a river that is forced to flow in a circle, with no downstream river bends for the leaves to reach. Even if you haven’t observed tea leaves, you have probably noticed that the surface of the stirred liquid is higher near the “bank” and lower in the middle of the cup. 

If you have read this far, you will probably also want to read the original article by Leopold and Langbein here, and a brief description of Einstein’s thought experiment here. For those of you who have wondered why that narrow “Marshy Lake” just to the east of Lake Miller is located where it is, the explanation was provided by Einstein. “He also noted that because the helical flow possesses inertia, the circulation (and the erosion) will be at their maximum beyond the inflection of the curve. Hence, the wave-form of the river will migrate in a down-current direction.” The Marshy Lake is the remnant of an ancient channel where the scouring effect of the helical flow created a channel that is still too deep to be invaded by the cypress forest.  

The episode gives a quick explanation of why there is helical flow on the outside of river bends. The water goes down as it hits the outer bank. That's why, if you're on the San Marcos, for example, you need to keep away from the outer bank or keep your bow pointed well away from the apparent direction of flow, toward the inside of the curve, by 20-30˚ or even more, depending on the speed of the water. If you don't, you'll slam into the outer bank.

I was paddling it at rather high water once, and my bow paddler was confused about the "as hard as you can" part of "Do draw strokes towards river center". We hit the bank so hard he was ejected forward. Surprise!!

There is a detailed description of the physics involved in the link to "meander" in Wikipedia. It also gives a good description of the forces that make streams, well, meander, and why sand/gravel bars form on the inside of river bends. Like Buffalo Bayou. It's what they do.

Today (Feb. 1, 2021), Radio Station KUHF ran a brand-new episode in the series “Engines of Our Ingenuity”. The speaker is Dr. John Lienhard, who founded the series in 1987. The title is “Our Rivers Meander”, which is Program Number 3248 in the series. The accompanying photos are great, including one of Brays Bayou. And, be sure not to miss the video version, which includes lots of spectacular aerial images.

On Tuesday Feb. 2 at 9:00PM, radio station KUHF will air this week’s edition of the TED Radio Hour. The subject will be “Our Relationship With Water”. There are four talks, ranging in length from about 6 minutes to 16 minutes.

Here are the titles:

How Did We Lose Our Connection To Water?

What Is The Human Cost Of Toxic Water And Environmental Racism?

How Can We Prepare For The Next Hurricane Katrina?

What If Lakes And Rivers Had Legal Rights?

This show will be rebroadcast on KUHF at 5:00PM on Saturday Feb. 6, and it can also be accessed as a podcast at https://www.npr.org/programs/ted-radio-hour/