A sensor for measuring erosion and deposition
The processes of sediment transport and deposition entail questions of the frequency of transport, the threshold of transport, the migration ofbedforms, and the sedimentation and resuspension of sediments carried in suspension. The study of these processes demands the simultaneous monitoring of the process agencies, i.e., the current and the waves, and the response at the sediment-water interface.
In the past, two main approaches have been used to measure changes in bottom elevation in the wave-influenced environment: optical methods, using a time-lapse camera or a video-camera (e.g., Davies 1985), and acoustical methods, using a high-frequency echo-sounder mounted at some distance above the bottom (e.g., Wright et al. 1986). However, not even an echo-sounding frequency of 1 MHz can give a resolution better than a few millimeters, which is not always quite adequate (e.g., in areas of low intensity processes, plane bed transport, or when studying ephemeral mud blankets). Both the echosounder and the cameras are quite bulky and will disturb the flow pattern if they are put too close to the point of study. At longer distances the cameras are severelylimited by suspended sediments, notably at just those events that are of most interest. Furthermore, video cameras produce an enormous amount of data that is not readily interpretable by computers.
The present instrument, the 'sedimeter' (patent pending), is also optical in that it uses light as an information-carrier, but due to its operating principle it is not disturbed by suspended sediment or colored water. The disturbance of the flow pattern associated with it is small and rather constant.