Note: This is the first article in a series on sand mine best management practices. It focuses on insufficient natural buffers between the mines and the San Jacinto river. Subsequent posts will focus on land clearing, site reclamation practices, and more.
A comparison of sand mining actual and best management practices found that performance shortfalls in local mines exacerbate sedimentation in the San Jacinto River, contrary to assertions by the Texas Aggregate and Concrete Association (TACA) that sand mining has environmental benefits.
Proximity of mines to San Jacinto River in non-flood conditions.
TACA claims that when a river floods, the current is so weak that sand and sediment are deposited inside of mines. An analysis of satellite and aerial photos shows, though, that the current is strong enough to break dikes, destroy roads, re-route the river through mines, and carry sediment downstream.
TACA sounds eerily reminiscent of Richard Pryor when his wife caught him in bed with another woman. “Who you going to believe? Me or your lyin’ eyes?”
In at least one case, a broken dike has gone unrepaired for years while pollution continues to escape into the San Jacinto, the main source of water for Lake Houston and millions of people.
Dangers of Sand Mining
Numerous states and countries acknowledge the following risks of sand mining. Most impose regulations on the industry because sand and silt washed downstream from mines can:
- Impair water quality
- Increase water treatment costs
- Impair wildlife and fish habitat
- Reduce carrying capacity of rivers and streams
- Reduce the volume of lakes
- Block drainage ditches
- Contribute to flooding
- Impose dredging expenses on taxpayers
- Ruin recreation
Louisiana: Leader in Communicating Best Practices
The Louisiana Best Management Practices Guide to sand mining is one of the most concise, candid and clearly written guides in the world. Government and industry developed it together. The refreshingly honest introduction states:
- “Sand and gravel mining operations can potentially cause off-site impacts to water quality if site planning and BMPs are not factored into every aspect of the mining operation.”
- “…BMPs … should be utilized … to prevent pollutants from leaving the mining operation.”
- “Siltation is considered the highest nonpoint source priority of concern in wetland areas and the second highest priority affecting lakes (1992 Report to Congress).”
- “Mining related activities have been estimated to cause 7 percent of the nation’s nonpoint source impacts to lakes and 17 percent to coastal waters.”
Comparing Texas Practices to Other Areas’
Texas does not make it clear what the state’s best management practices (BMPs) for sand mines are. So how do sand mines along the San Jacinto measure up to other states’ and countries’ guidelines? Not well.
One focus of their BMPs is the use of buffer zones, setbacks and strips of vegetation to reduce erosion and control sedimentation. The minimum distance between mine and river in most cases is 100 feet. Some specify more.
- Alaska, for instance, discourages mines from locating within 1000 feet of a public water source, i.e., the San Jacinto which feeds Lake Houston, the main drinking water source for millions of people. The minimum near other bodies of water in Alaska is 200 feet.
- Malaysia specifies a 50 meter setback (164 feet) from all river channels.
- Australia prohibits sand mining in sensitive areas altogether.
In Texas along the San Jacinto, miners often excavate to within 40-50 feet of rivers, and remove vegetation to build dirt roads on the remaining narrow strip between the mine and the river. These thin, sandy barriers provide little defense against floods. They have been repeatedly breached, as you will see below. The river often runs right through mines, carrying sand and sediment downstream.
Types of Barriers against Sedimentation
Louisiana mandates a minimum 100-foot buffer adjacent to perennial streams. The state recommends a dual defense against sedimentation: vegetation and structural measures. Their best practices guide states, “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. Topsoil should be added where existing soils are not suitable for adequate vegetative growth.”
Vegetative controls include:
- Maintaining buffer zones between mine and river
- Sod stabilization techniques. Sodding can be more than 99 percent effective in reducing erosion.
- Protection of trees involves preserving and protecting selected trees that exist on the site prior to development.
- Temporary and permanent seeding
Structural controls include:
- Diversion ridges, berms or channels of stabilized soil
- Silt fences
- Sediment basins with banks sloped at 2:1 or less
- Dikes – Must be well compacted and vegetated, with an outlet pipe or coarse aggregate spillway
- Riprap protection – at the outlet end of culverts or channels to reduce the depth, velocity and energy of water so that the flow will not erode the receiving stream.
- Check dams – Small dams less than 2 feet high constructed across swales or drainage ditches to reduce flow velocity and erosion.
- Aggregate stabilized site entrances – at least 50 feet long to reduce sediment tracked onto public roads. Tire washing may also be needed.
- Good housekeeping practices for fuel, debris, sediment from unstabilized areas, etc.
- Post-construction stormwater management measures
- Retention ponds
- Vegetated swales and natural depressions that filter sediments from runoff with side slopes of 4:1 or less.
A Visual Comparison
Note the images below. The first represents the ideal; it is taken from the Louisiana BMP guide. The rest are from the West Fork of the San Jacinto in the last three years.
Image of ideal stream bank from Louisiana Sand Mining Best Practices Guide. Note vegetation, grass, gradual slope and aquatic plants.
West Fork Sand Mine, 9/14/2018. During Harvey, 150,000 cubic feet per second came rushing down this narrow channel and flooded 20 square miles of exposed sand in more than a dozen different mines.
Consequences of NOT Following BMPs
The image above and the following images all come from a small area of investigation shown below.
2.1 miles from Northpark Drive and US59, and 3.1 miles upstream from the US59 bridge.
The following images demonstrate what happens when miners work too close to the river. Numbers on the first image correspond to close-ups that follow.
Inundation of sand mines during Harvey on 8/30/17. Numbers correspond to close-ups below. All photos courtesy of Google Earth.
1 – Rapids within sand mine.
2 – Water rushing into mine, creating turbulence.
3 – Water takes a shortcut across meander through mine.
4 – Washed out road INSIDE sand mine during Harvey.
5 -Sand bars within sand mine in conjunction with ruptured dikes prove sand was carried downstream. Photo taken on 10/28/2017 (after Harvey).
In a white paper circulated among Texas state legislators called The Societal and Environmental Benefits of Sand Mining. TACA insists, “When [water invades a sand mine during a flood], the velocity of the water slows significantly, losing its ability to keep sediments in suspension and the stream or river begins to deposit its sediment load. When flood waters back into an area where a sand and gravel pit is located, the pit becomes a sediment trap for the flood waters and their sediments.” This series of photos directly refute TACA’s claims.
Why do we allow sand mines to operate in areas that flood repeatedly and violently, so near the drinking water source for millions of people?
Un-repaired Dike Still Leaks Sediment after 3 Years
Are the mines following Best Management Practices? The dike on the right in the images below ruptured in 2015 and still has not been repaired. Note sediment streaming into the West Fork.
Dike ruptured during flood in 2015 (see image below). It continues to spew sediment into the river.
Geologists say that once a river “captures” a sand mine, it repeatedly tries to take that same route in subsequent floods. This is a direct consequence of mining too close to the river.
Cautionary Advice from India
Sustainable Sand Mining Management Guidelines from India state, “Floodplain Extraction should be set back from the Main Channel. In a dynamic alluvial system, it is not uncommon for meanders to migrate across a floodplain. In areas where sand and gravel occurs on floodplains or terraces, there is a potential for the river channel to migrate toward the pit. If the river erodes through the area left between the excavated pit and the river, there is a potential for “river capture,” a situation where the low-flow channel is diverted though the pit. In order to avoid river capture, excavation pits should be set back from the river to provide a buffer, and should be designed to withstand the 100-year flood… Adequate buffer widths and reduced pit slope gradients are preferred over engineered structures which require maintenance in perpetuity.”
Sand Miners Externalize Costs
Because these West Fork sand mines did not consider violent floods in their design and construction criteria, taxpayers downstream bear the cost of remediation. Dredging of the West Fork will cost tens of millions of dollars – for the initial 2.1 mile phase alone! That doesn’t even include recurring and unnecessarily high costs of water treatment because of turbidity.
Posted 6/24/18 by Bob Rehak
299 days since Hurricane Harvey