Comparison of measurement techniques for monitoring sediment transport under field conditions, in the Scheldt estuary

The Dutch and Flemish Governments set up an integrated monitoring program, MONEOS, which will follow up on the development of physical and ecological system characteristics of the Scheldt estuary. An important part of the program focuses on the quantification of the sediment transport. Within the program, a wide variety of sediment transport measurement devices is available, both for near-bed and suspended sediment transport. However, for practical reasons, it is preferable to work with a limited set of equipment only. This study aims to (1) evaluate the performance of different sediment transport measurement devices available, under field conditions, and (2) determine an optimal equipment configuration for monitoring purposes in the Scheldt estuary. Two extensive field campaigns, covering a full tidal cycle, were performed in 2008 and 2009 using a total of 12 direct (Delft Bottle, pump sampling) and indirect (acoustic and optical) measurement techniques. Analysis of measurement data consisted of calibration of the continuous measurements with the results of the pump samples and comparison of the silt and sand transport rates obtained with the different methods. Interpretation of the measurements from individual instruments was complicated by the presence of both sand and silt, variation in particle size over time and the occurrence of flocs during most of the experiment. Results show similar trends in transport and concentration time series for nearly all instruments. However, large differences exist in absolute transport and concentration values, especially for peak-concentrations.