6/23/25 – Two West Fork pit captures caused by floods in early 2024 are now more than a year old and untouched.

“Pit capture” is when a river punches through the dikes of a sand mine and starts flowing through it.

Photographs taken on 6/22/25 from a rented helicopter show that the San Jacinto West Fork continues to flow into and through the two sand pits. Their dikes have not been repaired. And the river has rerouted itself through the pits which are on private property. See below.

Here’s a video shot in May 2024 while flying from one end of the mile-long pit to the other.

At the northern end of the Hallett mine, the West Fork has captured another pit.

Best management practices recommend minimum 100-foot-wide, reinforced dikes to eliminate problems like this. That obviously wasn’t the case here.

So, do pit captures encourage or discourage downstream sediment buildups that contribute to flooding?

Industry Says Sediment Falls into Pits. But Does It?

The sand mining industry would have you believe that the pits capture all sand that flows into them. That may be true in certain instances and not in others.

It depends on speed of the water. During the May 2024 flood, I used a drone to measure the speed of floodwaters moving through one of the pits at 5 MPH.

The table below shows particle sizes that water moving at various speeds can transport.

Sediment Size	Diameter (mm)	Approx. Critical Flow Velocity for Initiation
Clay/Silt	<0.004	~0.5 ft/s (~0.34 mph)
Very Fine Sand	0.004–0.062	~1.5 ft/s (~1.0 mph)
Fine Sand	0.062–0.2	~2 ft/s (~1.3 mph)
Medium Sand	0.2–0.5	~3–4 ft/s (~2–2.7 mph)
Coarse Sand	0.5–2.0	~4–5 ft/s (~2.7–3.4 mph)
Very Coarse Sand	2.0–4.0	~5–6 ft/s (~3.4–4.1 mph)
Small Gravel	4–16	~6–7 ft/s (~4.1–4.8 mph)
Medium Gravel	16–64	~7–10 ft/s (~4.8–6.8 mph)

Conclusions:

1. Sediment deposited in pits is not permanently trapped.
2. Floods can churn up and flush out stored sediment.
3. Sediment transport becomes episodic and pulse-like.

Modeling studies show that even in pits 20-25 feet deep, floodwaters at 5 MPH can mobilize and carry away all but the largest gravel. Consequently, experts say sand-mining pits do not serve well as permanent sediment sinks. But are they adding to the sediment load downstream?

How Pit Capture Can Add to Sediment Loads Downstream

Numerous studies have examined whether pit capture makes downstream sedimentation better or worse. Generally, they indicate that pit captures tend to make downstream sedimentation worse—especially over the long term.

To summarize, these sources generally conclude that pit capture:

• Increases downstream erosion through “hungry water” effects.
• Results in channel instability and sediment pulses.
• Worsens downstream sedimentation, contrary to any short-term sediment-trapping benefit.

Therefore, management efforts typically and strongly recommend preventing pit capture through:

• Better engineering practices
• Increased setback distances
• Reinforced berms
• Strategic sediment management planning.

For More Information or a Summer-Science Project

For those interested in learning more or for a summer-science project, consult the following:

Peer Reviewed and Technical Studies:

• Kondolf, G.M. (1997). “Hungry water: Effects of dams and gravel mining on river channels.” Environmental Management, 21(4), 533–551.
• Kondolf, G.M. (2001). “Geomorphic and environmental effects of instream gravel mining.” Landscape and Urban Planning, 28(2-3), 225–243.
• Kondolf, G.M. et al. (2007). “Two Decades of Geomorphic Effects of Gravel Mining in the Tuolumne River, California.” Environmental Management, 40, 571–584.
• Collins, B.D., & Dunne, T. (1990). “Fluvial geomorphology and river-gravel mining: A guide for planners, case studies included.” U.S. Geological Survey Special Report 98, California Department of Conservation.
• National Marine Fisheries Service (NMFS) (2004). “Gravel Mining and Channel Stability: An evaluation of gravel extraction impacts on salmon habitat.”NOAA Technical Memorandum NMFS-NWFSC-66.
• NMFS (2011). “Channel Processes and Sediment Transport: Implications for Salmon Habitat Restoration.” NOAA Technical Memorandum NMFS-NWFSC-115.

Texas-Specific Agency Reports:

• TWDB (2020). “Lake Houston and San Jacinto River Watershed Study: Sediment Management and Flood Risk Assessment.” Texas Water Development Board, Austin, TX.
• Texas Commission on Environmental Quality (TCEQ) (2019–2022). Multiple investigation and enforcement reports documenting pit breaches and sediment spills from sand mines along the San Jacinto River (publicly available through TCEQ’s Central File Room and online database).
• TCEQ (2021). “Best Management Practices for Sand Mining in the San Jacinto River Watershed.” RG-555. Texas Commission on Environmental Quality, Austin, TX.
• Texas Parks and Wildlife Department (TPWD) (2018). “Impacts of Gravel and Sand Mining on Instream Habitats and Fish Communities in Texas.” TPWD Inland Fisheries Division Technical Report IF-TM-2018-01.
• SJRA (2021). “San Jacinto Regional Sediment Management Plan.” Harris County Flood Control District and SJRA joint publication.
• Army Corps and HCFCD. “West Fork San Jacinto River Emergency Dredging Project Final Report (2019).”
• “San Jacinto River Master Drainage Plan – Appendix F: Sediment Management (2021).”

Background and Context:

• Langer, W. H. (2003). “A General Overview of the Technology of In-Stream Mining of Sand and Gravel Resources, Associated Potential Environmental Impacts, and Methods to Control Potential Impacts.” USGS Open File Report OF-02-153.
• Bull, W.B., & Scott, K.M. (1974). “Impact of mining gravel from urban stream beds in the Southwestern United States.”Geology, 2(4), 171–174.

Posted by Bob Rehak on 6/23/25

2855 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.