Reducing Floodplain Width Increases Flooding, Erosion

Many floodplain regulations focus on not restricting the conveyance of rivers. But the high dikes of many sand mines literally wall off half their floodplains. This can increase the frequency, duration, and severity of flooding opposite the mines as well as erosion of river banks.

West Fork Mines at I-45 Provide Example

The case of Emil Shelbebon who operates a 200-acre motorsports complex on the south bank of the San Jacinto West Fork at I-45 provides an excellent example. Sand mines on the north side of the West Fork built high walls near the river bank. LIDAR surveys taken before and after construction of the dikes suggest the dikes may be higher than 20 feet in places. That’s the height of a 2-story building.

According to the computer models of engineers, that raises the height of floods on Shelbelbon’s property 3-4 feet above what they would otherwise be – especially in less than 100-year floods – when water can’t spread out on both sides of the river.

All that extra water concentrated in a smaller space also increases the velocity of flood waters and erosion. Shebelbon says he has lost 7 acres since the mines built their walls.

Schematic Diagrams Illustrate Principle

In principle, it looks like the series of diagrams below.

#1. Floodplains naturally spread out on both sides of river.
#2. In a minor flood, water spreads out in both directions.
#3. But after a mine walls off the floodplain, water can spread out in only one direction, raising the height of floods on the other side.
#4. The extra volume of floodwater now forced into a smaller space increases the velocity of floodwater. That, in turn, increases erosion, too.

The last point may be the hardest to understand. Here’s an imperfect analogy that helps to illustrate it. Most of us have put our thumbs over nozzles of garden hoses to spray dirt off driveways. Decreasing the width of the opening forces water to go faster after it leaves the hose. That peels dirt off the driveway faster. While a hose is a closed system and a river is open, the increased velocity increases erosion regardless.

Photos Vividly Illustrate Danger

This first photo shows the height of the sand mine dike north of Shelbelbon’s property.

Looking NE from over West Fork San Jacinto. That white line in the background is I-45. Note how dikes are half the height of mature trees.
Looking NW over part of Shebelbon’s motorsports complex towards mine. Note how Shebelbon’s property is at river level, but dikes around mines wall-off floodway.
Looking West from over Shebelbon’s property at river level. Compare height of dikes on right.
Looking ENE toward I-45 from over Shebelbon’s property, which is at river level. Note height of dikes on opposite shore. Shebelbon has lost 7 acres since the mines built their dikes.

The same problem exists on the San Jacinto East Fork.

Texas Concrete’s dike on left towers above homes on right. San Jacinto East Fork runs between them.

Perpetual Unintended Consequences

The dikes of these mines are intended to control stormwater within the mine and prevent the escape of sediment. Unfortunately for the people near them, they can have unintended side effects. And those side effects can impact neighbors long after miners abandon mines.

Texas regulations do not require restoring the natural contours of a floodplain when mines are done mining. So miners typically leave dikes in place…along with debris they’d rather not clean up.

Looking SW toward Shebelbon property from over I-45 across abandoned mine (bottom left). Google Earth shows activity on this site before Harvey but not after.

The Montgomery County Appraisal District (MCAD) values the 31-acre abandoned mine at $15,570 despite the fact that it’s right next to I-45 in the fast growing corridor between The Woodlands and Conroe.

MCAD classifies it as “wasteland/floodway.”

Montgomery County Appraisal District

A company named 45 SRL INC owns this property. The Texas Secretary of State shows that Williams Brothers Construction Company Inc. owns 100% of 45 SRL INC.

Williams Brothers is the largest highway contractor in Texas, one of the largest in the country, and claims to have completed more than $12 billion in projects. The company says it does 95% of its work for TxDOT.

Reclamation of this site would cost far more than the value of the land which likely explains why:

  • The property has been abandoned without reclamation for more than 3 years
  • Why we need performance bonds to ensure the reclamation of mines
  • Why Shebelbon will continue to flood in minor events.

If it can happen to a man with a thriving business, it can happen to you, too.

Posted by Bob Rehak on 12/19/2020

1208 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.