Benthic ecology flumes are used to study the interaction of organisms with the surrounding flow regime. A laser-line bottom-relief scanning system was added to an existing flume channel instrumentation consisting of a sensor positioning carriage with an acoustic Doppler flow sensor. The laser is also mounted to the carriage and it is focussed on a spot of the sediment surface which is situated right below the sampling cell of the flow sensor. Both devices are though measuring on the same horizontal position, one on the bottom and the other in the water column. Accuracy tests of repeated measurements at defined heights showed an error of less than 0.3 mm, but also revealed the importance of a careful calibration. A set of experiments on a sand mound and an upright cylinder was performed with combined relief and flow measurements to test the spatial coherence of these two methods. The flow results showed typical patterns of vertical deflection and vortex formation around the obstacles, matching with previous descriptions from literature. The bottom shapes obtained from the relief scans after an erosion experiment also reproduced literature knowledge. They endorse the flow measurements and thus indicate that the flow and relief data complement each other. Hence, the laser system is a valuable supplement for the flume instrumentation. In addition, erosion rates and volumes of transported sediment can be calculated from the results of the relief measurements. |
