Tag Archive for: dike

Earth Week Part 4: Slope of Sand Mine Dikes, Riparian Vegetation and Cost Offsets

Yesterday, I posted about how greater setbacks from rivers could improve safety for sand mines and downstream residents. Setbacks reduce the potential for erosion, sedimentation and consequent flooding. Here’s a related post that shows what happens when you try to build too close to rivers.

Note repairs to dike. I took this photo two weeks after Harvey.

First, understand that the closer you mine to the river, the steeper the slope of dikes must be. At a certain point, the slope becomes so steep that:

  • Grasses and trees can’t take root in it.
  • The loose soil becomes prone to erosion.
  • During floods, water in the river rises faster than in the pit.
  • It exerts pressure on the dike.
  • The dike can collapse through one of more of several mechanisms (piping, erosion, overtopping, sloughing, etc.)
  • The river invades the pit.
  • Depending on the depth of the pit, the volume of sediment in it, and the force of the flood, sediment could be carried downstream.

Another factor leading to dike collapse in the photo above is the road built on top of it. Running heavy equipment over the sandy soil causes it to compact and push outward. Vehicle traffic also keeps vegetation that could bind the soil from growing.

Accidents Waiting to Happen

It doesn’t take a Harvey-scale flood to breach these loose dikes. The unmemorable July 4th flood of last year breached the dike shown above.

Another flood on December 7th last year breached a dike in another sand mine downstream from the first one in three places!

Repairs to one of three dike breaches at a sand mine in Dec. 7 flood last year. Photo by Don Harbour Jr.

Here’s another breach at the same mine that hadn’t yet healed when I photographed it on September 28th last year.

Site of a breach in the dike of a sand mine. Note how the loss of vegetation has led to erosion and sloughing in the sandy soil.

When such breaches happen on both sides of a point bar, the river will “capture” the pit by rerouting through it – the shortest distance between two points.

West Fork sand mines on 8/30/17, one day after the peak from from Harvey

West Fork vs. East Fork and Value of Riparian Vegetation

Almost all of these problems could be solved by greater setbacks from rivers. That would retain more natural riparian vegetation and allow lower, more gradual slopes on dikes. It would also allow additional re-vegetation to take hold.

Shooting across the West Fork from on top of the dike shown in the first photo above. Note how loose the soil was in the foreground and how difficult it is to establish vegetation on the opposite shore in the middleground. Floods have torn away the erosion blankets trying to establish grass on the steep slopes.

Imagine 131,000 cubic feet per second ripping through a channel like this. That’s how much came down this portion of the West Fork at the peak of Harvey. It’s easy to see how the river could erode these dikes and invade the mines.

That’s why we need greater setbacks. It will allow more conveyance through the normal channel. And if we just leave native negation in place, it should help hold the dikes in place.

Now contrast the images above with this one taken on a portion of the East Fork where there are no sand mines.

Lush riparian vegetation and trees held the banks in place during Harvey.

Here’s another.

Offsetting Opportunity Costs with Conservation Easements

Mother Nature’s solution to sedimentation is free. If we could only just learn to respect the river and its flood plains. Yes, there would still be some sedimentation to deal with, but not nearly as much.

The loss of sand close to the river is an opportunity cost, not an out-of-pocket cost. Groups like the Bayou Land Conservancy can help offset some of that opportunity cost by providing income in exchange for conservation easements. I wish miners would explore this option more…for everyone’s benefit including theirs. It certainly might reduce their legal costs.

Posted by Bob Rehak on April 27, 2019

606 Days after Hurricane Harvey

Sand Mine Dike Breached 3 Times in 1 Week During Minor Flood

I’ve posted dozens of times about the dangers of mining in floodways. A local canoeist, Don Harbour, Jr., paddled down the West Fork of the San Jacinto twice during the last flood. He says he saw three breaches in one sand mine. The water was moving too fast to get pictures of all three, he says, but he did manage to get several shots. They eloquently illustrate the dangers of mining so close to the river.

Harbour, Jr. says he paddled by this mine on Saturday, December 8, and noticed water rushing into it.

River breaching into mine. Photo courtesy of Don Harbour, Jr.

The following Wednesday, December 12, he paddled down the river again and saw the reverse.

Sand mine sending sediment into river as flood went down. Photo courtesy of Don Harbour, Jr.

On that same trip, he photographed the owners frantically trying to plug the leaks in dangerous conditions.

Repairs to other breaches. Photo courtesy of Don Harbour, Jr.

Altogether, Harbour, Jr. says he saw three breaches in one mine in one week.

I have seen video of a fourth breach at the same mine last August. It appeared as though it was created with a backhoe. Six months later, the TCEQ says it is still investigating the August breach.

When Pro Business Means No Business,
It’s Time to Rethink Mining in Floodways

Breaches allow the escape of sand and silt. They contribute to the buildup of sediment dams in the river. Those then contribute to downstream flooding.

When a rain that averaged only 5 inches across the watershed breaches the dike of one mine three times in one week, it’s time to rethink mining in floodways.

Such dangerous business practices can reduce growth.

  • The growth rate in the Humble ISD this past year dropped from 6% to 1% due to flooding, in part, caused by sedimentation.
  • 44% of the businesses in the Lake Houston Chamber were damaged or destroyed during Harvey.
  • 100% of the businesses in Kingwood Town Center and Kings Harbor were damaged or destroyed.

Move Miners Back from River

We don’t want to drive miners out of state; we just need them to move out of the floodway.

We don’t allow unsafe vehicles on the road. Why do we allow unsafe mining on the river?

Here’s the dike of another mine farther upriver. I took this picture shortly after Harvey. But the same dike breached again during the July 4th flood this year.

Sand mines on the West Fork come right up to the river where floodwaters repeatedly breach dikes.

Texas is the only state that has no minimum setbacks of mines from rivers. In contrast, Alaska allows no mining within 1,000 feet of a public water source. Other states and countries establish erosion hazard zones taking into account factors such as:

Many geologists and engineers believe erosion hazard zones represent a safer approach to determining setbacks.

Posted by Bob Rehak on December 21, 2018

479 Days since Hurricane Harvey

Sand Mine Dike Remains Open for Years

In my last post, I talked about how certain sand mines on the San Jacinto could help reduce the rate of sedimentation in the river by following best management practices (BMPs) found in other areas. Those BMPs included:

  1. Locate mines outside of floodways.
  2. Establish performance bonds to cover the cost of cleanup.
  3. Increase the width of dikes.
  4. Decrease the slope of dikes.
  5. Control erosion with vegetation.
  6. Replant areas not actively being mined.
  7. Avoid clearing areas that will not soon be mined.
  8. Protect stockpiles from flooding.
  9. Mine only above the thalweg (deepest part of the river).
  10. Establish performance bonds to guarantee remediation of breaches and/or repurposing of mined areas once mining is complete

This Mine Missed 9 out of 10

The State of Texas does not require these BMPs for sand mines on the San Jacinto. But it should. Here’s a case study in what happens if you ignore these principles.

The wide shot below was taken in January of 2010. Notice the muddy brown area in the middle of the shot. Also notice the breach in the dike on the left hand side of the brown area and the stockpile right above it. Finally, notice that un-vegetated area in the point on the far left.

That’s where the original mined area was back in the 1980s. Whoever mined it at that point took sand directly from the river bank. Regardless, it was never replanted and the entire area remains vulnerable to erosion to this day.

That’s important because this mine, like all but one on the the West Fork, lies largely in the floodway. See the cross-hatched area below in the USGS flood hazard map.

As a result of being in the floodway, here’s what happened to it during Hurricane Harvey. Note multiple breaches in the dikes, the loss of the stockpile, and swirling floodwaters flowing through the mine from upper left to lower right. Finally note that Harvey inundated that original mined area that was not replanted.

This made me curious, so I reviewed the historical imagery for this location in Google Earth. Here’s the same mine in 2016. Same story. Just not quite as bad. They lost about a third of the stockpile. And nasty brown water flowed straight through the pits closest to the river.

Next, I zoomed in on the breach and scrolled back through time. It first showed up in 2006.

By early 2011, they were building roads out to the breach.

Here it is in late 2011. Note how the river below the breach has become clogged with sand.

In 2013, still wide open. Another flood. More sediment flushed downstream.

In 2014, still open!

In 2016, they’ve rebuilt the dike! But it’s skinny. Very vertical. Un-vegetated. And you can already see cracks and major signs of erosion developing in it.

Then along comes another flood at the end of the year.

And by the next day, most of the dike has been washed away.

By 2017, it was fixed again.

Then along came Harvey. And there it went again.

Spike the Dike

So how did this mine score overall? If you were applying these principles, it received an almost unperfect score.

  1. Locate mines outside of floodways.
  2. Establish performance bonds to cover the cost of cleanup.
  3. Increase the width of dikes.
  4. Decrease the slope of dikes.
  5. Control erosion with vegetation.
  6. Replant areas not actively being mined.
  7. Avoid clearing areas that will not soon be mined.
  8. Protect stockpiles from flooding.
  9. Mine only above the thalweg (deepest part of the river).
  10. Establish performance bonds to guarantee remediation of breaches and/or repurposing of mined areas once mining is complete

The breach first showed up in 2006 and was still open in 2014! Goin’ for the record! How much sand and sediment wound up downstream as a result?

No telling exactly. But whatever it was, they won’t be picking up the tab for the cleanup. You will be (Point #10)…which underscores the need for the State to adopt common sense guidelines like these. Perhaps if it had, we wouldn’t have had as much damage during Harvey.

As always, these are my opinions on a matter of public policy, protected by the First Amendment of the U.S. Constitution and the Anti-SLAPP statutes of the great State of Texas.

Posted on August 3, 2018 by Bob Rehak

339 Days since Hurricane Harvey