In addition to in-situ sampling and the use of optical turbidity meters, the study of sediment transport in river systems can be enhanced by the use of Acoustic Doppler Current Profilers (ADCPs) since they provide simultaneous measurements of velocity and concentration. A recent development, the so-called horizontal ADCP (HADCP), can be installed on one river bank, facing the other in order to provide continuous measurements of flow. Results are presented from a study site which is 4-m deep, 90-m wide and is equipped with three horizontal ADCPs operating at 300 kHz, 600 kHz, and 1200 kHz, respectively. Attenuation data are presented from two events during which suspended solid concentrations exceeded 1g/L. Although the profiling range of these instruments is limited by the depth of the river, we find that they provide reliable measurements of concentration when concentrations exceed ~0.1 0.4 g/L, depending on the operating frequency of the instrument. The concentration time series obtained from the various H-ADCPs are in good agreement with one another and with values from in-situ sampling and simultaneous measurements of optical turbidity. Grain size estimates are obtained from an inter-comparison of the attenuation data for the three operating frequencies. The grain sizes that are found are in good agreement with values from laser grain sizing. The ability of H-ADCPs to measure suspended sediment concentrations during floods is very promising for their use in sediment transport surveys in rivers, since sediment fluxes are greatest during floods.