ABSTRACT
The initiation and development of the bedforms in alluvial rivers have dramatic effect on the flow resistance and sediment transport. Therefore, precisely measuring the size and shape of the bedforms is one of the bases for further study on the mechanism of water and sediment interactions. Due to the technical limitation, measurements on the bed forms of the river were mostly a static prototypes bed, could not reflect the development of the shape of the bed caused by their movement. On the other hand, experiment in a flume usually measure no more than a single point, which do not reveal spatial distribution of the bed form, especially for a three dimensional sand wave. In this research, a measurement system for monitoring the dynamic movement of bedforms in a flume was developed. The system consists of a hardware system and a data acquisition software system which collecting flume bed elevation data automatically at a certain interval. Ten independent underwater ultrasonic distance sensors with a diameter about 10 mm were employed in the system. Ten sensors were arranged as a T-shape or Triangle shape as a whole, as shown in Figure 1, nearest distance between two sensors were 30 mm. The data of ten different positon of the bed elevation can be measurement synchronously. Because of the novel arrangement of our sensors group, temporal and spatial variations of the bedforms, especially the small scale change at different position, can be analyzed conveniently. The bed form measurement system would provide more precise, reliable and abundant data for the study of bed form morphology over different flow conditions. Sensor arrangement. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315623207/4fbc492d-6678-4a12-aaf6-5c2b8ea38e5f/content/fig219_1.tif"/>
Three runs of experiments have been conducted in a 50 m long, 1 m wide and 1.2 m height flume. uniform sand with 0.9 mm diameter were employed in the experiment. The elevation variation of the mobile bed were measured by the monitoring system. Three runs of test, representing the nearly immobile bed, micro sand waves bed and large number of successive dunes, respectively. The validity of the measurement system was verified at different experiment conditions. The results show that the development and characteristic parameters of bedforms are different under different flow conditions. The height, length, shape of the sand waves and their migration velocities, were determined and analyzed based on the measured data. These key parameters would provide invaluable insight for the research of the effect of bedforms on the flow and the sediment transport.
