Pit Capture on Caney Creek: What Happens When A Sand Mine Builds Flimsy Dikes in Floodways

This story illustrates on of the dangers of pit capture in sand mining. During the peak of Imelda, 42,000 cubic feet of floodwater per second came down Caney Creek. However, early the morning of September 19th, residents south of the Triple PG Sand Mine on Hueni Road in Porter started seeing water coming from the mine before it came up from the creek.

Escaping with Only a Minute to Spare

They started evacuating their families and animals. One Walden Woods resident told me that the water came up so fast, it covered an entire SUV within an hour. Another told me that had she waited one more minute to evacuate, she and her family would have had no way out. The force of the rushing water undermined the house and garage of a third. Farther south of the mine, residents of Dogwood Lane, Woodstream Village, Dunnam Road, and Riverchase felt the same panic.

Caney Creek Captures Triple PG Sand Pits

So what happened? A review of aerial photographs below taken on 10.2.19, almost two weeks after Imelda, showed a massive breach in the northern dike of the mine. Erosion patterns suggest the water then rushed through the mine in a north to south direction.

  • Trees laid down in a southerly direction at the entry point
  • Sand waves orient along the north-to-south direction of flow
  • East/west roads separating the ponds were blown out, by water flowing north to south
  • The mines main stockpile shows massive erosion along its western edge in a north-to-south direction
  • Sand is piled up against the mine’s main building along the northern side only (where the water came from)

Photo Tour of the Aftermath

All the photographic evidence suggests a classic case of pit capture. Peach Creek joins Caney Creek just north of this entry point.

Where water entered the mine from the north. Looking northwest from inside the mine and past the northern dike. Note the trees pushed into the mine by the force of the water, indicated the direction of flow.
Reverse shot. Looking south into the Triple PG Sand Mine.
A closer view of the same scene shows clear evidence of erosion within the mine from rushing floodwaters. The water came from directly behind the camera position. The road in the middle was blown out, but reconstructed by the time I shot this photo two weeks after Imelda. The TCEQ said they could not safely reach this part of the mine because of damaged roads.

You can see from the shot above that water barreled through this mine as if shot from a water cannon.

Close up of repairs to damaged road. Looking southwest. Sand patterns show water moving north to south.
Note the sand pushed up against the north-facing back of this building.
The eastern side of this stockpile was eroded from the bottom by water side-swiping it from a north-to-south direction.

No Effective Dike at Southern End of Mine

There really is no dike at the southern end of the pit, just a road around the perimeter. The ground level in the neighborhood to the south is virtually even with the level of the road. After water flowed through the pit, it flowed through neighborhood(s) to the south and damaged homes. It’s easy to see the damage immediately south of the pit and imagine the pit capture as the cause of the damage. The damage faces the mine, not Caney Creek to the east.

Floodwaters from the Triple PG mine partially knocked this home off its foundation. The owner had to jack it up and re-level it. The back of the house faces the mine and is not more than a hundred feet from it.
The same homeowner’s garage. Floodwaters from the mine scoured under it. Again, the back of the garage faces the mine and is not more than a 100 feet from it.

Reasons for Pit Capture

What is pit capture? It’s when a river or stream cuts through the pit of a nearby sand/gravel mine instead of following its normal course.

How does it happen? Water starts to overtop or penetrate the dike. It creates a fissure that rapidly widens and opens a hole. Pretty soon the dike collapses and the water rushes in. The water moves from areas of high pressure and elevation to areas of low pressure and elevation. After the water moves into into the pit, it fills the pit up and needs to find a way out on the other end. Like a water ballon attached to a faucet, sooner or later dikes on the other side burst.

Why does this happen?

  • The mine was built in the floodway of Caney Creek on a point bar
  • Dikes made out of sand could not withstand the force of the water
  • Dikes had previously failed in the same places and left “weak points”
  • When the water came up, it took the path of least resistance
  • Texas has no minimum setbacks from rivers for mines
  • Texas enforces no best management practices for mines

What Next for the Triple PG Mine?

The Texas Attorney General is currently suing the mine for allowing its process water to pollute Lake Houston. The mine left its dikes open for weeks after multiple breaches in multiple storms. The TCEQ also found that the mine was breached from east to west between White Oak and Caney Creeks.

Potential fines could reach well past a million dollars. That raises the question, “What can be done with this mine to protect residents below the mine and to protect the City of Houston’s water supply?”

Over the years, Triple PG’s owners have removed 800 acres of forest and an unknown volume of sand from the mine. The risk of pit capture is greatest were mines are deeper than the adjacent river bed and close to the river/stream. Both conditions apply in this case.

The dike between Caney Creek and the Triple PG pit is a narrow strip of unvegetated dirt, just wide enough to support a vehicle…and not compacted very well as you can see below.

This shows repairs to an exit breach to Caney Creek farther south. No geotextile fabrics or rip rap are holding the repair together. Photo courtesy of Josh Alberson. Taken 11.2.2019.
This closer shot shows the same breach filled with sand and clay. You can see how flimsy the repair is. The uncompacted and unprotected soil is already eroding after two inches of rain last week. Photo courtesy of Josh Alberson. Taken on 11.2.2019.

It will be interesting to see whether a professional engineer will certify this repair, as a restraining order demands.

If the courts should shut this mine down, sealing it off permanently will be difficult and costly.

Posted by Bob Rehak on 11.3.2019 with images from Josh Alberson

796 Days since Hurricane Harvey and 45 since Imelda

The thoughts in this post reflect my 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.