This study describes an experimental system for making continuous river discharge measurements using real-time, image-based, noncontact technologies. The system uses particle image velocimetry (PIV) to estimate displacements of river surface flow tracers on recorded images. The velocity-area method is then applied to estimate discharge at a cross section of known bathymetry. The system has been operational since August 2004, making continuous discharge estimates at an experimental site on the Iowa River. Based on preliminary results from its first 23 months of operation, the authors identify illumination of the river surface by natural lighting, wind, and rain effects, PIV parametrization for variable flow conditions, and stage measurement, as the most pressing challenges related to image-based discharge measurement. The experimental data archive generated from the continuous long-term operation at the site will facilitate the research needed to address these problems and improve the reliability of image-based discharge measurement technologies.

The present paper reports results obtained with image velocimetry to provide new insights into the two‐phase nature of sediment‐laden flows. The resulting two‐phase flow perspective is compared with the traditional mixed‐flow (or combined phase) perspective that treats sediment‐laden flows essentially as flow of a single fluid. The insights are from flume experiments entailing the use of fully suspended natural sand and neutrally buoyant particles conveyed in a turbulent open channel flow of water. They confirm that suspended particles (irrespective of particle density) may affect a turbulent flow throughout its depth. Suspended particles modify flow turbulence, the main effects quantified being decreases in the bulk water velocity and in the von Kárman constant, while the flow's friction velocity remains approximately constant. Comparison of the results obtained with the two particle densities reveals differences in particle influences on water flow. In the flows conveying sand the characteristics of water and particle movement are strongly coupled, yet distinct; that is, there is a lag in the mean velocity between local water and particle movement, and intensities of water turbulence differ from intensities of particle motion turbulence. These results confirm and extend prior two‐phase flow perspectives on suspended‐particle transport and indicate the inaccuracies in some assumptions associated with the mixed fluid formulation of suspended‐particle transport.

In spite of the extensive use of acoustic-Doppler current profilers (ADCP) for measurement of velocity and discharge in open-channel and riverine environments, a rigorous methodology for estimating ADCP discharge measurement uncertainty that follows current engineering standards for uncertainty analysis is not yet available. In this paper, we apply the broadly accepted engineering standard for uncertainty analysis put forth by the American Institute of Aeronautics and Astronautics in 1995 (AIAA) to develop a framework for the estimation of uncertainty in ADCP measurements from a moving boat. First, we summarize the terminology and methodology of measurement uncertainty analysis and review the data reduction equations used by ADCPs to estimate the total discharge in measurements from a moving boat. Second, we discuss briefly the various elemental error sources that contribute to the uncertainties of the ADCP measured variables, which in turn contribute to the total uncertainty of ADCP discharge measurement...