Rampaging East Fork Floodwaters Cut New Path Through Plum Grove Sand Mine

The sign outside the abandoned Texas Concrete Sand and Gravel Mine in Plum Grove tells readers that an RV resort is coming soon. They might want to rethink that concept. Yesterday, rampaging floodwaters destroyed most of the mine except for a small area near the entry on FM1010.

Classic Example of Pit Capture

The East Fork rerouted itself right through the heart of the mine, sweeping away almost everything in its path. The river swelled to more than half a mile wide and ruptured dikes in at least four places when the river rose 10 feet in 24-hours.

The East Fork at this location rose 15 feet in three days, 10 of those in one day.
Normal course of river is red line on west side of mine. During flood, the river broke through the dike on the north side. Then floodwater filled the mine like a water balloon which burst in multiple places on the south side. Water now follows the yellow line.

This is a classic example of what geologists call pit or river capture. The East Fork entered the northern side of the mine and exited at multiple points on the south. Current coming out of the mine exceeded that in the river itself, carrying mud and muck downstream.

Flooding Based on Less than 10-Year Rain

The gage at this location indicated Plum Grove received only 3.36 inches of rain over a three-day period. However, up to 8 inches fell upstream from here, primarily during a two-day period. Jeff Lindner, Harris County’s meteorologist characterized the rains that produced the flood as, “Generally less than a 10-year event for the 48-hour time period.”

Pictures Taken on 5/3/2021

I took all of the shots below on 5/3/2021, three days after the major portion of the rain fell on April 30.

Looking north at the northernmost portion of the mine. The river appears to have entered the mine in this area. Note the dike in the far distance that’s not visible in the tree-line on the left.
Wider shot, still looking north toward entry point shows white water ripping through mine.
Looking south, you can see that the water in the mine is now higher and faster than the water in the river to the right.
Still looking south toward FM2090, now the only way in and out of Plum Grove. FM1485 is closed due to high water and FM1010 was washed out during Harvey by runoff from Colony Ridge to the southeast.
Looking north across FM2090. Where the water exits the mine, you can see that the force of the main flow is now misaligned with the bridge opening.
The width of the mine is now the width of the river…plus the river. Only the entry of the mine at the upper right remains above water at this time.
Looking east from over FM2090.

Danger of 2090 Washout in Next Big Flood?

Unless someone reroutes the river back to its original course and fixes the dikes, the current through the mine will continue to erode the banks of the roadway at the top of the image above.

These images dramatize the need for real sand-mining reform in Texas. There’s some evidence that Imelda did the same thing to this mine two years ago. But the TCEQ forced the company to repair the dikes. Now that the miners are gone, who will do that?

Plum Grove was lucky that upstream rains only amounted to a ten-year event. A larger storm could have cut the City and Colony Ridge off from the only viable evacuation route. More than 20,000 people would have been affected.

Posted by Bob Rehak on 5/3/2021

1343 Days since Hurricane Harvey and 592 since Imelda

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.