Characterization of uncertainty in the measuring of bottom transport using ADCP

During several monitoring campaigns in the Scheldt estuary, ADCP’s (acoustic Doppler current profilers) are deployed to measure the water velocities and discharges. The acoustical backscatter intensity of the ADCP’s are commonly used to estimate the suspended sediment load. When the measurement platform with down-looking ADCP is kept stationary, the bottom tracking measurement principle can be used to detect and estimate the bed load transport. However, the measurements of the bottom tracking is experimental. To assess the uncertainty of these measurements, a flume (W = 1.2 m, L = 25 m and H ADCP's (different types) are installed above the sand bed. Measurements of bed load transport velocity from the bottom tracking feature are performed. Different settings of the instruments are tested and compared, together with a range of flow regimes. Also optical measuring techniques (camera’s, turbidity sensor) are used, both down-looking and side-looking. The side-looking cameras are installed to map the depth (and also velocity) of the mobile layer above the bed. Down-looking cameras are installed to look in a restricted view area to follow the individual sediment grains in the bottom-top layer. Combining, the pictures with PIV or PTV algorithms, the velocity of the individual sediment grains can be detected. The different measurement techniques are compared