A physically based method of combining ADCP velocity data with point samples to compute suspended-sand discharge -- Application to the Rhone River, France

Measuring suspended-sand flux in rivers is a challenge since sand concentrations are highly variable in time and space throughout a river cross section. Most of the present methodologies rely on point or depth-integrated sampling (Nolan et al., 2005, Topping et al., 2016). The standard method estimates mean concentration and multiply it by discharge to compute the suspended-sand discharge. Here, we demonstrate methods of combining point suspended-sediment samples with ADCP (Acoustic Doppler Current Profiler) high-resolution depth and velocity measurements to improve vertical and lateral integration of concentration and flux. A preliminary version of this method is applied to data collected in the Rhône River in Lyon, France, during a 10-year flood in January 2018. Two options for vertically integrating the measured suspended-sediment concentrations were tested whereas lateral integration was based on nearest-neighbor interpolation only, as a baseline option. Sand flux results are similar, thus suggesting that vertical integration options may be less critical than lateral integration options that will be implemented and tested in future work.