Impact of sand mining on alluvial channel flow characteristics

Abstract

Mining pit in a channel bed causes disturbance to the flow characteristics. To interpret the phenomenon of change in flow characteristics in a mining pit, experimental study was performed in a tilting laboratory flume. This research focuses on the impact of mining pit on different turbulent parameters, such as flow velocity, Reynolds shear stress distribution, turbulent kinetic energy fluxes, and higher order moment distribution. We have observed dropped in flow velocity in the pit and also significant reversal velocity layer at the pit bottom. The analysis of Reynolds shear stress and higher order moment distribution shows higher values of velocity fluctuations in the pit than the upstream section. The response of bursting events, which is identified by the third order moment, shows influence of sweep events near the bed in all four sections. Third order moment analysis also shows a rise in dominance of sweep events along the flow depth in the pit and it’s downstream, compared to the upstream section. The kurtosis distribution shows highly intermittent nature of turbulence close to the channel bed. The longitudinal turbulent kinetic energy fluxes and vertical turbulent kinetic energy fluxes are in downstream and downward directions for both inner and outer layer in the pit region, which shows an increase in bed particle mobility in that region, whereas it is present only in the inner layer at the upstream section. Additionally, improved bed load transport equation by incorporating pit geometry has been proposed for alluvial channel subjected to sand mining.