Examining downstream impacts of riverbed dredging

Sand pit mining is a crucial source of sand, gravel, and other aggregates used in the construction industry. These materials are dredged from riverbeds, causing disruptions to the downstream flow of the river in the process. These disruptions can impact the flow of the river and the ecology of the downstream environment, leading to unforeseen consequences for human settlements and wildlife.

Arora et al. conducted laboratory-scale experiments to understand the effects of mining pits on a downstream riverbank. Their controlled method allowed the team to pinpoint the effects of the mines.

“A huge advantage of the experimental approach was the ability to control the test conditions so that only the effect of a mining pit on the riverbank hydromorphology could be analyzed,” said author Bimlesh Kumar.

They found that downstream of the mining pit, the river flow turbulence is greatly affected, with increased turbulence within the flow over the bank slope and near the bank toe. This can exacerbate riverbank erosion over time.

While it is possible to implement solutions to reduce this erosion, it can be challenging to determine the precise effect they will have, given the complex nature of real-world rivers.

“We suggest soft engineering measures of bank protection like natural vegetation, riprap, boulder coverings, and geotextiles on the bank slopes,” said Kumar. “But questions need to be addressed before suggesting any solution, like how far downstream or upstream the effect of mining is present, if the impact is the same for meandering rivers, or how a cohesive bank will respond to mining.”

Source: “Higher order turbulence statistics and multiscale characterization of morphodynamics in a riverbank section with an upstream mining pit,” by Sukhjeet Arora, Abhijit D. Lade, and Bimlesh Kumar, Physics of Fluids (2023). The article can be accessed at https://doi.org/10.1063/5.0159014 .