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“Geology on the Wing” Wednesdays #4 – Point bar and counter point bar, Brazos river

August 25, 2011

The Brazos river runs from the high mountains of New Mexico all the way down to the Gulf of Mexico, meandering through almost all of Texas.  It is relatively unmodified by humans (as American rivers go), and thus displays great fluvial architectures.  The water level in the river in this photo was quite low, due to severe drought all across Texas this year.  The river itself is about 20 m wide, for you scale freaks.

The photo below shows a few point bars and counter point bars on the Brazos near Houston, TX.  The point bars grow on the inside of a meander bend, and result from growth of the meander by expansion/swing (the outward growth of the bend).  New Orleans is built on a point bar, if I am not mistaken.  On the other hand, counter point bars grow on the outside of a bend (a nice one is just left and below the center of the image) due to translation/sweep (the downstream migration of the river).  Some rivers predominantly sweep and some swing; still others, like the Brazos, show beautiful examples of both.  For a nice paper on counter point bar development, see this pdf.

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