At the abandoned Williams Brothers sand mine on the San Jacinto West Fork, a strip of land – approximately 400 to 500 feet long and up to 50 feet wide – collapsed into the river during the flood in late January.

The dramatic erosion, during a relatively minor (2-5-year) rain event, dramatizes the destructive power of moving water and the need for greater setbacks from the river for sand mines. It also raises questions about abandonment plans for sand mines.

Resident Photo From Boat Shows Collapse

A resident who frequently boats the river and wishes to remain anonymous supplied the picture below. As the resident said, “All that dirt went somewhere. And it didn’t go upstream.”

Aerial Shots Show Extent of Damage

From the air, the same location looks like this.

Where Trees Once Stood

Compare that with the satellite image below from Google Earth taken last year. Note how there used to be a row of trees on each side of the road. Now, trees remain only on one side.

Most of the trees on the river side of the road are now floating down the river somewhere.

Blankets of Fresh Sand Everywhere

The resident who took the first shot above (the one from the boat) has lived near the river for 40 years. He says he’s never seen so much fresh sand deposited in a flood. See below.

The images above show the power of moving water. One cubic foot of fresh water weighs 62.4 pounds. And more than 20,000 cubic feet per second moved down this reach of the West Fork during the peak of the January flood. That’s a lot of force on sandy soil.

We Must Plan for River Migration

That force was magnified by the way a river meanders. On the outside of curves, water accelerates. That extra speed accelerates erosion and creates what geologists call the cut bank.

Conversely, water travels less far and slower on the inside of a curve. As a result, sand is often deposited there in what geologists call point bars. Learn more in this post about Why Rivers Move.

Over time, erosion on one side of a river and deposition on another tends to exaggerate curves. Geologists call that process river migration. River migration already broke through the dike of one sand mine slightly upstream.

During the January flood, water flushing through that mine likely contributed to the buildup of sand blocking the Northpark drainage ditch near Northpark Woods.

Note in the photo above that the Northpark Ditch is now blocked by sand higher than ditch itself. This blockage suddenly appeared during the Jan. ’24 flood. It is backing water up toward Northpark Woods and Oakhurst in the upper right. At least some of the sand was likely flushed out through the breach in the dike above.

Need Greater Setbacks from the River For Sand Mines

As I stated in the beginning, this dramatizes the need for greater setbacks from the river for sand mines. At one time, there was no minimum distance.

In November 2021, after years of work by Bill McCabe and the Lake Houston Flood Prevention Initiative, TCEQ adopted new Best Management Practices (BMPs) for sand mining in the San Jacinto River Basin.

The new rules specify “A minimum 100-foot buffer zone is required adjacent to perennial streams greater than 20 feet wide, 50 feet for perennial streams less than 20 feet wide, and 35 feet for intermittent streams.”

Clearly, that may not be enough. For a list of what other states specify, see the Sand Mining page of ReduceFlooding.com.

Posted by Bob Rehak on 2/27/2024

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