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.
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.
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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2021/05/20210503-DJI_0661.jpg?fit=1200%2C900&ssl=19001200adminadmin2021-05-03 15:45:402021-05-04 07:53:21Rampaging East Fork Floodwaters Cut New Path Through Plum Grove Sand Mine
In the next two months, I expect to see legislation filed that will strengthen regulations on sand mining. Hopefully, legislation will prevent dangerous practices by the mining industry that have put residents at risk in the past.
Perhaps we can compromise on legislation that lets miners exercise their property rights without harming the property rights of others…or their incomes, safety, and families.
This is another post designed to raise awareness of sand mining problems and how other states have solved them. One of the main problems with sand mining in Texas: virtually all miners locate their mines in floodways. That almost guarantees a phenomenon called pit (or river) capture. Washington State has discovered the following about pit capture.
“Regardless of the best planning and intentions, impacts of flood-plain mining may simply be delayed until the river is captured by the … pit,” they say. “While capture may not occur in the next 100-year flood event, it is likely to occur in the future as development and consequent flood magnitude increase. In the long term, stream capture by (sand and) gravel pits is a near certainty.”
Consequences of Pit Capture
The paper cites more than three dozen examples of pit capture. Consequences include:
Lowering the river bed upstream and downstream of mining operations
River bed erosion and (or) channel incision
Bank erosion and collapse
Undercutting of levees, roads, bridge supports, pipelines, utility towers and other structures
This short YouTube video may help you visualize how this process works. A company called Little River made it with funding from the EPA and State of Missouri. Little River specializes in table-top, tank experiments for science classes. This video shows how pit capture happens and how erosion results.
Depending on the area and depth of the pit, and sediment volume carried by the river, it could take “millennia” to restore the natural environment after pit capture.
Operators’ attempts to prevent pit/river capture by armoring dikes and channelizing rivers often accelerate floodwaters and increase erosion downstream, say the authors (page 13 and figure 17) .
Cures for Pit Capture
The Washington State Department of Ecology Shoreline Management Handbook recommends locating mining activities “outside the shoreline jurisdiction.” They recommend 200 ft. from the floodway or off the 100-year flood plain. The latter coresponds to Texas regulations for the John Graves Scenic Riverway District on the Brazos River.
Immediate Reclamation for Each Segment
The Washington State Department of Natural Resources administers their Surface Mine Reclamation Act (RCW 78.44). It generally requires reclaiming mines immediately after each segment is mined. The 1993 revision of this law requires that most mines in flood-plain environments be reclaimed as beneficial wetlands.
The immediate reclamation requirement could benefit Texans. Texas law requires sand miners to file a reclamation plan to obtain a permit. However, there is no requirement to execute the plan before leaving the property. Many simply walk away from their obligations, much to the detriment of surrounding property owners and the safety of the public. Requiring miners to reclaim one section of a mine before permitting another would give them a powerful incentive to reclaim land.
The authors conclude: “If mine plans call for sites on flood plains, then wide, topographically higher, and thickly vegetated buffers should be considered as a means of reducing the probability of river avulsion in the near term. However, in most instances, buffers only delay the inevitable.:
“Determining an adequate distance between the flood-plain mine pit lake and the river will depend on understanding the rate of river meandering and the risk of avulsion.”
As always, these are my opinions on matters of public policy. They are protected by the First Amendment of the United States Constitution and the Anti-SLAPP statutes of the Great State of Texas.
Posted by Bob Rehak on August 13, 2018
441 Days since Hurricane Harvey
00adminadmin2018-11-13 21:03:562018-11-14 09:45:03Whose Property Rights are More Important? Yours or Sand Miners’?
Advanced economies, they say in their introduction, require large amounts of aggregate (sand and gravel) to sustain growth.Aggregate makes up 80% of concrete and 90% of asphalt pavements.
Many see floodplain mining as a safer way to obtain this aggregate than in-stream mining, but floodplain mining still poses substantial threats to river stability.
Dangers of River Capture
As we saw on the West Fork of the San Jacinto during Harvey, floodwaters take a shortcut through mines that are built on point bars inside meander loops.
Sand bars within sand mine, caused during “river capture” of the mine. These bars prove sand was carried downstream. This photo taken on 10/28/2018 (after Harvey) also shows repairs to mine wall. During floods, the river tries to cut across meanders, runs through the mines and carries sand downstream.
The authors say this can lead to:
River bed degradation
Infrastructure damage or destruction
Loss of riparian vegetation
Degradation of water quality.
Their review of local, national and international case studies showed that pit capture and subsequent river channel changes, are a common consequence of floodplain mining.
Changing River Environment and Putting Infrastructure at Risk
In their conclusion, Ladson and Judd state, “Although floodplain gravel mining has been considered a safer option than the direct extraction of gravel from a river, substantial risks to river stability and river health values remain. Floodplain gravel mining can cause change in the riverine environment, both locally and distant to the mining site, and in the short and long term.”
“There are substantial risks to infrastructure if river diversions occur which trigger bed and bank erosion.”
“There may be a role for river management agencies to influence the amount of mining that is undertaken, and the manner in which it is undertaken, in order to mitigate these threats.”
Mechanisms of River Capture
Another study goes into more detail. This second study, was conducted by Jacobs Engineering in 2015, also in Australia. It describes the processes behind river capture, the risks, and how to reduce them. It is titled Risk_assessment_of_floodplain_mining_pits_in_the_mid-Goulburn_Valley, The Golburn River, like the San Jacinto, meanders through relatively flat land. It also has approximately the same number of sand mines that the San Jacinto has.
Jacobs identified three risk scenarios for river capture:
Lateral migration of river channel into the pit
Sub-surface piping into pits and subsequent failure of pit walls
Flow of water into and through the pit and subsequent erosion of the buffer strip between the channel and the excavated pit.
Some San Jacinto Mines Push Recommended Safety Margins
Jacobs assesses (page 19) that 100 meters is the minimum setback to prevent river capture from occurring. In some places on the San Jacinto, dikes are less than 15 meters wide.
Jacobs also assesses that river capture is almost certain (page 19) where the basement of the pit is more than 5 meters lower than the river. San Jacinto sand miners are mining at more than double that depth.
“The physical processes of pit capture have been well documented from case studies: incision upstream and downstream of the pit are expected, with bed adjustments continuing until the river establishes a new equilibrium and grade,” says Jacobs.
Ways to Mitigate Risk of River Capture
Jacobs identified two main ways (page 47) to reduce this risk:
Locate pits out of the 100-year floodplain
Implement controls such as levees, grade-control structures, pit setbacks, depth limits, and waterway diversions.
Sadly, all sand pits on the San Jacinto are already in the 100-year flood plain. Worse, all but one are at least partially in the FLOODWAY, which is defined as the main channel of the river during a flood.
Even more sadly, it appears that none of the measures in the second category are being applied to San Jacinto mines either.
Posted by Bob Rehak, July 22, 2018
327 Days since Hurricane Harvey
00adminadmin2018-07-22 01:46:312018-07-22 01:46:31How Floodplain Mining Can Lead to River Capture