Remote monitoring of volumetric discharge employing bathymetry determined from surface turbulence metrics

Current methods employed by the United States Geological Survey (USGS) to measure river discharge are manpower intensive, expensive, and during high flow events require field personnel to work in dangerous conditions. Indirect methods of estimating river discharge, which involve the use of extrapolated rating curves, can result in gross error during high flow conditions due to extrapolation error and/or bathymetric change. Our goal is to develop a remote method of monitoring volumetric discharge that reduces costs at the same or improved accuracy compared with current methods, while minimizing risk to field technicians. We report the results of Large‐Scale Particle Image Velocimetry (LSPIV) and Acoustic Doppler Velocimetry (ADV) measurements conducted in a wide‐open channel under a range of flow conditions, i.e., channel aspect ratio (B/H = 6.6–31.9), Reynolds number (ReH = 4,950–73,800), and Froude number (Fr = 0.04–0.46). Experiments were carried out for two different channel cross sections (rectangular and asymmetric compound) and two bathymetric roughness conditions (smooth glass and rough gravel bed). The results show that the mean surface velocity normalized by the depth‐averaged velocity (the velocity index) decreases with increasing δ*/H, where δ* is the boundary layer displacement thickness and that the integral length scales, L11,1 and L22,1, calculated on the free‐surface vary predictably with the local flow depth. Remote determination of local depth‐averaged velocity and flow depth over a channel cross section yields an estimate of volumetric discharge. Key Points: Local depth‐averaged velocity is determined from velocity index multiplied by surface velocity Free surface integral length scale is correlated with the flow depth Volumetric discharge is determined from a single remote imaging device