Influence of pit geometry and flow conditions on sand pit migration in fluvial systems: insights from flume experiments

Pit migration can significantly disrupt stable fluvial systems, leading to abrupt changes in river morphology and ecology. This study investigates sand pit migration through lab experiments by varying pit shapes, sizes, and inflow discharge, while using Kinect and a DSLR camera to measure bed profile evolution. Repeatability tests ensure experimental consistency. Observations show that the rate of pit migration increases as the discharge increases. For rectangular pit, the migration rate is highest from 0.212 cm/min to 1 cm/min as the discharge increases from 5.12 litre/s to 6.94 litre/s. The migration rate of parabolic pits is lower than rectangular pits, and cylindrical pits take longer to fill at the centre than the sides. The migration rate of the cylindrical pit increases less (0.36 cm/min to 0.43 cm/min) as compared to the rectangular pit (0.212 cm/min to 1 cm/min). These findings highlight the influence of pit geometry and flow conditions on sediment transport.