Tag Archive for: pit capture

West Fork Still Running Through Sand Pits

8/6/24 – During Beryl in July, the San Jacinto West Fork continued to run through at least three abandoned sand pits. Mining companies still own two. A third has been sold to a residential developer for unknown purposes.

The river captured the pits earlier this year. “River capture” is a term used by geologists when floodwater breaks through a dike on one side of a pit and then bursts out the opposite site. That effectively reroutes the river. The phenomenon usually takes place in pits on a point bar and shortens the distance water must travel around them.

Sold by Hallett to Riverwalk Porter LLC

Hallett sold a 200-acre pit on the west side of the San Jacinto West Fork to Riverwalk Porter LLC shortly before the January floods this year. It was great timing for Hallett; not so great for the developer. See below.

West Fork, upper left, enters a 200-acre pit (left) that Hallett sold to Riverwalk Porter LLC shortly before the pit capture. Note how the normal riverbed is now blocked by sand. 8/6/24.
At the south end of the same pit, the river re-enters its normal channel. 8/6/24.

If Riverwalk Porter LLC planned to use this pit for stormwater detention, that will no longer work. They would be pumping water directly into the river.

Second Pit Still Owned by Hallett

A little farther north, the river cuts through another pit. Hallett still owns this one. The southern end of this pit (bottom of frame below) was left open for years until the Texas Commission on Environmental Quality (TCEQ) made Hallett fix it.

Now it’s open again…but on two sides. And the TCEQ has not yet taken action. I first observed this opening after May floods.’

Looking North. West Fork now cuts straight through the pit rather than going around it via its normal channel. 8/6/24.
Closer shot of bypassed channel at same pit. 8/6/24.

Williams Brother Pit

Just south of White Sands Drive in Porter, Williams Brothers abandoned a pit after Harvey. The company still owns the property. However they show no signs of re-establishing an eroded dike.

A narrow berm used to seal the pit off from the river at the top of the frame. The berm eroded during January floods then disappeared in May floods this year.

With the river now flowing into the mine, it is starting to erode a channel out of the mine.

Williams Brothers Mine after Beryl. Photo taken 7/9/24. River flows toward foreground.

In fairness, when the river is lower, the channel in the foreground does not yet convey water all the way back to the river.

Abandoned Pits Becoming Bigger Problem

At least four other companies have abandoned pits on the West Fork in recent years that represent potential issues:

What to Do?

I’ve been talking lately to residents neighboring these facilities. They worry about flooding related to the mines and how that can undermine their property values.

One resident that I interviewed today talked about growing up on the river before Lake Conroe, sand mining and his property flooding. He talked about clear water, abundant fish and plentiful wildlife.

I’ve been researching best practices for sand-mine abandonment and have some thoughts that I will share on the subject in coming days. I’m not sure we can get back to the way it was in the 1960s, but we can definitely do better. Check back in the coming days.

Posted by Bob Rehak on 8/6/2024

2534 Days since Hurricane Harvey and 29 since Beryl

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.

San Jacinto West Fork Reroutes Itself Through Giant Hallett Mine

Correction: This sand pit in this post was sold by Hallett to Riverwalk Porter LLC on January 23, 2024.

The San Jacinto West Fork has become totally blocked by sediment at the Hallett Mine in Porter and rerouted itself through the giant sand mine.

The old river channel has been sealed off by sediment. And the river now enters and exits one of the mine’s largest pits through large breaches in what used to be dikes. See below.

White oval shows location of blockage. Blue line shows old route of river. Red lines show detours through sand pit.

More than Normal Erosion

Rivers always move during floods through erosion. But this represents a far larger than normal amount of movement through a process called pit capture.

The river now runs through the Hallett pit instead of following its normal curving channel.

See photos below.

The loss of the dikes is likely the result of the SJRA releasing 71,000 cubic feet per second from Lake Conroe during the peak of the recent flood. That was the second largest release in the history of the SJRA.

Pictures taken just before the peak of the flood show the river already overtopping the pit’s dike. Dikes like walls that separate the river from the mine’s pits. They keep industrial wastewater out of your drinking water.

Weak Sand Mining Regulations Brought This On

Two other contributing factors are the depth of the pit compared to the river and the width of the dike.

  • The deeper the pit (compared to the river), the less stable the dike.
  • The narrower the dike, the weaker it is.

Until recently, Texas was one of the few states (if not the only one) that had no minimum setbacks of mines from rivers. Bill McCabe of the Lake Houston Area Flood Prevention Initiative was instrumental in lobbying for greater setbacks. The TCEQ adopted them in 2021, but this pit predated the new regulation. And the TCEQ did not enforce the regulation in this case.

In fact, this pit was open on its southern end since January. That breach was already expanding before the recent flood.

Pictures Taken Before and After Flood Show Pit Capture

Pictures taken during and after the flood show the impact.

Pre-peak on West Fork at Hallett Mine
Hallett Mine San Jacinto West Fork on May 3, near peak of recent flood.
Same area photographed on May 11, 2024. Break in dike is circled in red.

Following the river around to the right, you can see how much sand the river laid down. This likely happened when the volume of water moving through the channel decreased as the velocity decreased, allowing suspended sediment to drop out of suspension.

The river which flows right to left, used to flow toward the bottom left. But now it flows into the pit (upper left).
Closer shot showing the river being diverted into pit on the left.

This video shows the height of the sand deposited in the river bed when the river started flowing to the pit instead of following its normal channel.

Video courtesy of a fisherman, Jody Binnion. Listen to his narration.

This shot also gives you some idea of the height of the sand now blocking the river.
Farther upriver but looking downriver, you can see how the river has been diverted. Note how narrow the dike is/was as it approaches the point of failure.
Note the ripples on the water flowing into the pit.
At the far southern end of the pond, the water exits back into the river through this breach that opened up in the January flood.
Between the new entrance and exit from the pond, the Northpark ditch enters the river from Oakhurst and Northpark Woods.

Impacts Associated with Pit Capture

Without a river to remove sand from the confluence with the ditch, more and more sediment will likely build up here.

Academic literature discusses the impact of “pit capture” on:

  • River bed degradation
  • Bank erosion
  • Channel widening
  • Infrastructure damage or destruction
  • Loss of riparian vegetation
  • Habitat damage
  • Degradation of water quality.

In regard to the last point, sand mining also frequently stirs up heavy metals such as lead and cadmium, which have been documented in academic literature. However, I have no evidence that such chemicals are coming from the Hallett Mine.

This river, which now flows through the Hallett pit, flows into Lake Houston. And Lake Houston is the source of drinking water for more than 2 million people.

Posted by Bob Rehak on May 11, 2024

2448 Days since Hurricane Harvey

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.

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.

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.

West Fork Migrating Toward Proposed High-Rise Marina Project at 20 Feet Per Year

Steady northward migration of the San Jacinto West Fork could threaten the proposed new high-rise Kingwood Marina development – within the lifetime of many residents.

An analysis of satellite and aerial imagery in Google Earth shows that the river channel has shifted 758 feet north in 40 years – almost 20 feet per year – toward the site of proposed 25-50 story high rises. The proposed Kingwood Marina site is on the cutbank side of the West Fork. And the West Fork is definitely cutting.

Measuring River Migration Rate

These three images tell the story.

The white line shows where the original north shore of the river was in 1978. Image also shows location of proposed high rises relative to the river as it existed then.
This shows the river in 2017 after Harvey. The line shows the original location of the north shore in 1978. The river has shifted north by its entire width.
The measuring tool in Google Earth shows that the shift was 758 feet (length of the yellow line).

The migration of the river toward the high rises should continue. The river appears to be moving back toward one of its old meanders. The developer plans to build the high-rises in the old river bed. That’s a dangerous practice, because during floods, as residents all over Harris County discovered after Harvey, water seeks to return to old channels.

Floodway Shifting, Too

As the river moves closer to the high-rises, so will the floodway. Right now, the high-rises are built on the edge of the floodway that was mapped after Tropical Storm Allison in 2001. However, I believe that upstream development, river migration, and sedimentation are causing the floodway to expand and shift north. If current plans are approved “as is,” structures, people’s lives, and investor’s money will all be at risk.

Already at Greater Risk than Town Center

Harvey inundated Kingwood’s Town Center area. That’s a mile further from the river and on higher ground. About a year and a half later, approximately 25% of the businesses in Town Center still have not returned. That would certainly affect the economics of this development if it ever floods.

The proposed high rise development would sit on the edge of the cross-hatched area which represents the old floodway. These floods zones became effective in 2007, but are in the process of being updated in light of new data from three so-called 500-year storms in 2015, 2016 and 2017.

50 Years or Bust

At the current rate of northward migration, the river could reach the marina in about 50 years; it’s currently about a 1000 feet away. If the river “captures” the marina (just as it captures sand pits), we could expect to see a rapid shift in river migration toward the high rises. See the demonstration in the video below.

How rivers can suddenly jump when they get near big open areas like sand pits…or a marina.

Of course, before that happened, someone would try to prevent it. The owners would push to “shore up” the development with bulkheads or levees.

Futile Struggle to Combat Nature

Bulkheads didn’t work very well for these people on Marina Drive in Forest Cove.

Empty townhomes stand a mute witness to the destructive power of 240,000 CFS/second.

Levees have their own set of problems. And anyway, how do you put a level around a marina? Seems like building this close to the river is just asking for trouble.

Planned Construction Level Likely to Flood Every 4-10 Years

The developer wants to build the foundations up to 57 feet. That’s asking for trouble, too.

If you go back and analyze the crest data for the West Fork for the last 90 years, you will see that the river has crested higher than 57 feet nine times – once a decade. But you will also see that it has crested higher than 57 feet six times in the 25 years since 1994 – about once every FOUR YEARS!

Rivers! Look pretty. Get ugly.

Sometimes rivers remind me of that classic 1983 teen flick called War Games staring Mathew Broderick and Ally Sheedy. The duo hacks into a Department of Defense Computer and starts playing what they think is a game. It’s called “Global Thermonuclear War.” They quickly discover it isn’t a game; they’ve triggered the real thing. In the end, they discover that “the only winning move is not to play.”

That’s certainly the case with the West Fork.

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 statute of the Great State of Texas.

Posted by Bob Rehak on 1/26/19

515 Days since Hurricane Harvey

Whose Property Rights are More Important? Yours or Sand Miners’?

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.

Causes of Pit Capture

Sand-pit capture happens when pressure from floodwater breaks through dikes and takes a short cut across sand mines instead of following the river’s course. A scientific paper called “Flood Plains, Salmon Habitat, and Sand and Gravel Mining” by David Norman and C. Jeff Cederholm describes the process.  The paper, published in Washington Geology by their Department of Natural Resources, says pit capture is almost inevitable in the long term.

“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
  • Increasing suspended sediment
  • Deposition of silts

I have described how those consequences happen in several previous posts. Also, the paper describes the processes in detail, so I will not repeat the explanations here.

As in Washington, the Houston area has had many instances of sand-mine pit-capture.

Video Shows Simulation of Pit Capture

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.

Avoiding pit capture requires thorough and immediate reclamation because of river migration. The longer a pit goes before reclamation, the greater the likelihood that river migration will capture it. We saw an example of that on the San Jacinto. The river is migrating 12 feet per year and is 38 feet away from breaking into a major sand pit.

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.

Substitution of crushed concrete or quarry rock for gravel also has distinct environmental advantages.

Safeguards for Flood-Plain Mining if Necessary

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

How Floodplain Mining Can Lead to River Capture

In a previous post, I showed satellite and aerial images of water sweeping through a West Fork sand mine complex during Harvey. This is part of a process called river capture. In the photo below you can see the West Fork flowing into and through mines on both sides of the river during Harvey.

Dikes on both sides of the river were breached in the process. In fact, historical images in Google Earth show that they have been breached repeatedly.

During Harvey, floodwaters swept through this complex and breached dikes in multiple locations as the river took a shortcut through the mines. 

Highest Risk Scenarios for River Capture

A review of scientific literature reveals that the risk of stream diversion through pits (river capture) is increased by:

  • Proximity of pits to the river
  • Increased depth of the pit, particularly where the base of the pit is below the lowest part of the river.

The phenomenon seems common and the consequences well documented.

2014 Survey of Scientific Literature Finds 37 Examples

In 2014, Anthony Ladson and Dean Judd, two Australian researchers, found 37 instances of river capture in a review of scientific literature. They published their findings at the Seventh Annual Australian Stream Management Conference in a paper titled A review of the effect of floodplain gravel mining on river stability.

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
  • Bank erosion
  • Channel widening
  • Infrastructure damage or destruction
  • Loss of riparian vegetation
  • Habitat damage
  • 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:

  1. Lateral migration of river channel into the pit
  2. Sub-surface piping into pits and subsequent failure of pit walls
  3. 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