How Vegetative Controls Can Help Sand Mines Reduce Erosion and Flooding

During Harvey, millions of cubic yards of sediment moved downstream. Some came from river bank erosion. But some also came from exposed sediment in sand mines that flank both sides of the West Fork like the one below.

West Fork Sand Mine photographed May 5, 2021. Such mines occupy 20 square miles in a 20 mile stretch between I-45 and I-69.

It’s exceedingly difficult to determine the percentages that came from various sources. Regardless, sediment built up at key places, blocking both the West Fork and its tributaries. Those blockages backed water up into thousands of homes and businesses.

The mouth bar of the West Fork (photographed after Harvey) is now gone thanks to three years and more than $100 million of dredging. Ten feet of sediment was deposited in this area during Harvey, severely restricting the conveyance of the river and contributing to the flooding of thousands of homes and businesses.

Ever since then, the Lake Houston Area Flood Prevention Initiative has lobbied the Texas Commission on Environmental Quality and the Texas Aggregate and Concrete Association to adopt a comprehensive and improved set of best management practices (BMPs).

In yesterday’s post, I discussed setbacks from rivers, a major improvement in the new BMPs now being considered. Today, I will discuss vegetative controls in the Draft of Proposed BMPs, now in the public comment period. If observed, they could reduce sedimentation and flooding. If not, we could have more problems right here in River City. So please get involved.

Section 2.1 Vegetative Controls

Vegetative controls play a major role in minimizing soil exposure, erosion and runoff.

A large part of the new BMPs, Section 2.1, deals with vegetative controls. I summarize and liberally quote from that section below so that boaters, neighbors and community officials will know what the TCEQ expects mines to do. Also, the wording in one section should be strengthened to eliminate ambiguity. I will call it out below for readers so you can request the TCEQ to improve the language.

How Vegetation Helps Reduce Erosion

According to the TCEQ, “Vegetation is an inexpensive and effective way to protect soil from erosion. It also decreases erosion from flowing water by reducing its velocity. Roots hold soil and increase infiltration. In areas that are outside the active sand mining operation and not expected to handle vehicle traffic, vegetative stabilization of disturbed soil is required using the BMPs described below.”

Only Plants Appropriate for Region

“Vegetative controls must consist of plants appropriate for the ecoregion where the site is located and must not include any noxious or invasive species.” They then provide links to several acceptable lists.

Weekly Inspection Required

“Site operators must inspect and document disturbed areas of the site where vegetative controls have been implemented once every seven (7) calendar days. Operators must inspect all vegetative controls to ensure that they are installed properly, appear to be operational, and minimizing pollutants in discharges, as intended.”

A sentence farther down can be improved. “Operators must replace or modify controls [that have failed] in a timely manner, but no later than the next anticipated storm event.”

Opportunity for Improvement:

TCEQ never defines the “next anticipated storm event.” For the last month, widely scattered thunderstorms have caused street flooding in parts of Houston will leaving others untouched. No one can predict with certainty whether one of those storms will park over a sand mine. This gives the sand miners an opportunity to delay repairs almost indefinitely.

See suggested change at end of post.

2.1.1  Vegetative Buffer Zones

“Vegetative buffer zones are continuous undisturbed or planted vegetated areas that surround a development, land disturbance activity or that border an intermittent stream or permanent water body. Buffer zones aid in sediment filtration and removal by blowing surface water flow through these areas. Construction site runoff must be dispersed over the entire buffer zone if possible. A minimum 100-foot buffer zone is required adjacent to perennial streams greater than 20 feet in width, 50 feet for perennial streams less than 20 feet in width, and 35 feet for intermittent streams.”

Lack of a vegetated buffer zone allows sand from this stockpile to erode into White Oak Creek. Notice large swirls of sand cascading down the slopes into the creek.

2.1.2  Sod Stabilization

Sod stabilization involves establishing long-term stands of grass with sod on exposed surfaces. When installed and maintained properly, sodding can be more than 99 percent effective in reducing erosion.

During May 2021 floods, the East Fork San Jacinto swept through the abandoned Texas Concrete Sand & Gravel Plum Grove Mine. The area circled in red was exposed to floodwaters. See below.
Close up of area above taken two months earlier, but still after site was abandoned. No sod.

Protection of Trees

“Protection of trees involves preserving and protecting selected trees that exist on the site prior to development. Mature trees provide extensive canopy and root systems that hold soil in place. Shade trees also keep soils from drying rapidly and becomingsusceptible to erosion, as well as increasing property value. Consideration must be given to the tree root structure.”

“If trees die or are no longer viable for soil stabilization for any reason, then they must be replaced within 30 days with any equivalent or better soil-stabilizing tree.” 

2.1.3  Temporary Seeding

“Temporary seeding is the planting of fast-growing annual grasses to hold the soil in areas that will not be disturbed again for 30 or more days. For long-term protection (greater than one year), permanent seeding must be initiated. Mulching helps ensure seed growth and maintains soil moisture and helps prevent erosion. It is essential when slopes are steep, the weather is hot or dry, and soil conditions are not favorable.”

Ooops. Note steep, unvegetated banks on this West Fork dike in foreground which breached multiple times.

“Tillage, with lime and fertilizer, to maintain adequate soil pH and nutrient content, may be important before seeding.”

2.1.4  Permanent Seeding

“Permanent seeding is the use of perennial grass (with trees and shrubs) to stabilize the soil. Vegetation is often not fully established until one year from planting. Inspect, repair and re-seed as needed, evaluating choice of seed and quantities of lime and fertilizer. Use temporary seeding if the time of year is not appropriate for permanent seeding.”

2.1.6  Mulching

“Mulching is the placement of hay, grass, wood chips, straw, or synthetic material on the soil. Mulch holds moisture, lessens temperature extremes, and retards erosion on steep slopes during seed establishment. Soils that cannot be seeded due to the season must be mulched to provide temporary protection. Operators must apply the mulch in an appropriate manner that prevents the mulch from leaving the site during heavy rain events.”

2.1.7  Erosion and Sediment Control Blankets

“Erosion and Sediment Control Blankets are machine-produced mats of straw or other fibers held together with netting that provide temporary or permanent stabilization in critical areas, such as slopes or channels, so that vegetation may be established. These blankets often contain seeds to help establish vegetation.”

The Artavia Development in Montgomery County appears to be routing its main drainage ditch through this old sand mine. This area perpetually eroded. This swale covered by what appears to be an erosion blanket may help reduce that in the future. Note erosion already existing to left of blanket.

2.1.8  Surface Roughening

“Surface roughening, using heavy equipment, creates horizontal grooves across the slope which reduces runoff velocity/erosion and aid the growth of seed. Roughened slopes must be immediately seeded and mulched.”

To make this work, the slopes would need to be gentle enough to catch rainwater on its way to the pond or river. Unfortunately, you don’t often see gentle slopes in San Jacinto mines, if at all.

Summary and Call to Action

Virtually all of these BMPs call for regular inspections and maintenance. The most troubling part of them is the sentence highlighted above about the next “anticipated storm.” A sand miner could build a case for ignoring virtually all of these by claiming he didn’t anticipate storms anytime soon. But by the time a storm like Harvey or Imelda approaches, or even one of the May storms that dumped 7 inches of rain on Kingwood in three hours, it would be too late to replant vegetation. It needs time to regrow.

I suggest replacing “next anticipated storm” with “must repair or replace controls immediately when damage is noted during weekly inspections.”

Please submit your thoughts on this and other BMPs to the TCEQ by emailing with the subject line “BMPs Guidance Document” before August 19, 2021.

Posted by Bob Rehak on 8/12/2021

1444 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.