For the “Too Long; Didn’t Read” folks (you're missing out, but still check out the video and graphics below):
Clearing floodplain forests for sand and gravel mining sets off a chain reaction that reduces the ability to temporarily store water, which increases the severity of a flooding event, which increases recovery time.
Simultaneously, and/or stemming from these events:
An overflowing river can change course by flowing into an abandoned floodplain mining pit that is too close to the channel. Over time, the river begins to straighten, which increases water velocity, leading to more aggressive erosion of the riverbank. These occurrences create an unstable habitat for wildlife and increase the severity of a flooding event, again increasing recovery time. Riverbank erosion also pushes sediment downstream, which increases flooding risk downstream.
The Whole Story:
Until recently, I didn’t know that abandoned sand and gravel mines along the Amite River contributed to the 2016 floods in Baton Rouge, Denham Springs, Watson, and surrounding areas. I only learned about this issue when a classmate in the LSU Landscape Architecture program, Victoria Gough, presented her senior project on how to restore these abandoned sites to their natural, forested condition to act as flood buffers and to serve as areas for kayaking, fishing, and swimming. Victoria’s research during the last year of her studies helped her to understand how “60 years of floodplain sand and gravel mining has played a dominant role in the evolution of the Amite River.”
Reclaiming Abandoned Mines (Credit: Victoria Gough, RRSLA)
Having grown up along the Amite, but now a Landscape Designer at Pharis Design in Austin, Texas, Victoria explained that her family’s experience in the 2016 floods motivated her to study this issue. After nearly two years, Victoria’s family is still working to repair damage from three feet of water in their home.
While the precipitating factor of the 2016 floods was an unrelenting storm that dumped over 20 inches of rain over three days on East Baton Rouge and neighboring parishes, the resulting flash floods from the overflowing Comite and Amite Rivers caused devastating damage – nearly “50,000 to 75,000 structures flooded… and 13 people [dead].” *
Part of the reason the rivers overflowed into nearby, low-lying neighborhoods was because of direct and indirect effects of sand and gravel mining in the rivers’ floodplains. An important industry in this region, these mines are necessarily located near rivers because sand and gravel deposits naturally occur in floodplains.
While the act of sand and gravel mining itself does not cause flooding, three critical factors associated with floodplain mining contribute to the likelihood that the adjacent river will cause significant damage when inundated:
- Floodplain forest clearing;
- Mining pit proximity to river channel; and
- Mine abandonment without restoration or filling.
1. Trees, Make Way: Accessing sand and gravel deposits requires clearing the floodplain forests, which are buffers between land and water. These wetlands perform several essential tasks, such as:
- Helping to absorb excess water when the river is overwhelmed;
- Slowing the river’s current; and
- Reducing riverbank erosion by anchoring sediment with roots.
2. Heading for Rock Bottom: Mining creates deep pits, and since water always seeks the lowest point, mining in the floodplain too close to the river invites trouble. The video below, by Little River Research & Design, helps explain what can happen when a river meets a floodplain mine pit. Here are over-simplified explanations of a few technical terms:
- Pit Capture: When an overflowing river finds a mining pit in the floodplain close enough to the original channel, it rushes to fill the pit and, consequently, causes the river’s course to change.
- Hungry Water: The river normally carries suspended sediment particles, which help to ‘weigh’ down the water, but as the river fills the pit, this sediment drops and also begins to fill the mine, allowing the water to become lighter and to move more quickly and more aggressively downstream of the pit.
- Headcut / Incision: The water cutting away at the riverbank, eroding the sediment. Homes downstream and built close to the river are in danger of falling in as the base of the riverbank is cut away.
3. Left Wide Open: Decades of lax regulation of the sand and gravel mining industry in Louisiana have led to many mines being abandoned without restoration or even without being filled. Having seen the video, we now know why this is a bad idea.
The dangers of abandoned floodplain mines were not only acknowledged by the Louisiana statute RS 30:905.1 (Abandoned Mine Reclamation), but also led to studies commissioned by former Louisiana Governor Buddy Roemer and the U.S. Army Corps of Engineers. The statute even provides that there is supposed to be money (somewhere) to reclaim these mines.
Even for those of us who have grown up near rivers, it’s easy to forget how powerful a river is until it suddenly swells and rises during periods of heavy rain, surging down and threatening to spill out of the usual confines of its channel. Remembering this will help us to seek and advocate for solutions to preventable situations, such as ones abandoned mines threaten to create. I think we can agree with Victoria: “…I hope with the research and understanding of the Amite, this won’t happen to anybody again.”
*Advocate Staff Report. "What caused the historic August 2016 flood, and what are the odds it could happen again?" The Advocate 5 August 2017. <https://www.theadvocate.com/louisiana_flood_2016/article_3b7578fc-77b0-11e7-9aab-f7c07d05efcb.html>.