Turbulent flow structures and geomorphic characteristics of a mining affected alluvial channel

Abstract

Sediment mining in rivers may have a major impact on river geomorphology and research is required to quantify these impacts. In this research, experimental studies were conducted to analyse the morphological changes of channel bed and the turbulent characteristics of flow in the presence of mining. The channel bed profile shows erosion at the bank of the pit and that the erosion expands to the whole width of the channel and propagates downstream with time. The deposition of sediment occurs along the upstream edge of the pit and the depth of the pit decreases with time. Velocity reversal occurs at the central bottom of the pit related to a recirculation zone. Reynolds shear stress and the turbulent intensities become higher in the mining pit region and downstream of it as compared to the upstream section, causing a more rapid movement of bed particles. Analysis of the bursting phenomenon shows that the contribution of sweep and ejection events to the total Reynolds shear stress is more dominant over outward and inward interaction events. The dominance of the sweep event over ejection is observed at the near‐bed region for all the sections, but the depth range of dominance of sweep events in the pit and downstream of the pit is found to be more than the upstream. The increase in thickness is responsible for the increase in bed material transport. The increased sediment transport capacity at the mining pit and downstream of it caused the deformation and lowering of channel bed downstream. An empirical formulation of bedload transport for mining induced channels is derived from two different sized uniform bed materials. Copyright © 2018 John Wiley & Sons, Ltd.

On the Morphodynamic Alterations around Bridge Piers under the Influence of Instream Mining

“…The HEC-RAS model predicted heavy erosion on the upstream side of the pit, while CCHE2D predicted relatively higher downstream erosion. Experiments conducted by Barman et al [8] reported a rise in the turbulent stresses in the mining pit and at the downstream side of the pit.…”

Sand mining far outpaces natural supply in a large alluvial river

“…Over the past century, anthropogenic pressures associated with population growth, urbanisation, and economic development have seen an increase in the demand for the natural resources river systems provide Best and Darby, 2020). In particular, the demand for sand and gravel from rivers has seen unprecedented growth since the 1970s (Peduzzi, 2014;Miatto et al, 2017;Torres et al, 2017), with demand now outstripping supply (Bendixen et al, 2019). Estimates indicate that today, at a minimum, between 32 and 50 × 10 9 t of aggregates are extracted globally every year (Koehnken and Rintoul, 2018).…”

“…In order to effectively and sustainably manage riverine sand resources, accurate and regular monitoring of the locations and rates of sediment extraction are required (Peduzzi, 2014;Bendixen et al, 2019). Yet the pervasive and diffuse nature of the riverine extraction process means that it often occurs at spatial scales (spread across many square kilometres of river surface area) and in remote locations that make on-site monitoring difficult.…”

River bank instability from unsustainable sand mining in the lower Mekong River

“…Mining practices frequently target sediment from stores of sand (bedforms) on the river bed 22,23 . The removal of sand has been shown to alter the riverbed morphology, reduce flow velocities and increase flow turbulence around the mining pit areas 23,24 , sometimes with undesirable impacts. For example, there has been speculation that perceived increases in rates of bank erosion are caused by sand mining 8,14,23 -26 .…”