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Acoustic Doppler current profilers (ADCPs) are not able to accurately determine velocity near their transducers and near the bed. These limitations have restricted the use of ADCPs to flow depths that are large enough to allow acquisition of few directly measured velocity data that can be subsequently used to accurately estimate vertical velocity profiles and flow discharge in cross sections. While the causes that make ADCPs unable to collect data in the near-bed region are relatively well documented, the causes of near-transducer errors have not yet been fully understood and are only partly documented. We present results from an experimental study aimed at characterizing the systematic errors due to the combined effect of acoustic interference and instrument-induced flow disturbance near a Janus-configured ADCP. The study comprises: (1) concurrent measurements with an ADCP and an acoustic Doppler velocimeter (ADV) under the ADCP; (2) measurements of the flow disturbance produced by the ADCP in the vertical and horizontal planes; and (3) ADV measurements along the path of the acoustic beams ensonified by the ADCP during a measurement. Results suggest that ADCPs bias low the velocity profiles with respect to the undisturbed velocity profiles, mostly because of the flow disturbance induced by the ADCP, with acoustic effects playing a secondary role. For the range of flows we studied, both undisturbed and disturbed profiles exhibit similar shapes when plotted in dimensionless form, with the bulk flow velocity and the ADCP diameter (D) as characteristic scales. The differences between the undisturbed and the ADCP-disturbed profiles extend up to a distance of about 1.SD from the ADCP, except for the profiles measured at locations where the flow depth is close to D for which the boundary layer induced by the ADCP interacts with the one induced by the flume bed. DOI: 10.1061/(ASCE)HY.1943-7900.0000173 CE Database subject headings: Open channel flow; Flow measurement; Errors; Experimentation. Author keywords: Open-channel flow; River discharge; Flow measurements; Hydrometry; Acoustic Doppler current profilers; ADCP elemental errors; ADCP measurement uncertainty.

Measurements of water discharge and flow velocities in riverine and tidal environments are commonly made with acoustic Doppler current profilers (ADCPs) mounted on a moving boat. This paper presents results of high-resolution Large Eddy simulations (LES) conducted to investigate two elemental error sources in ADCP measurements from a moving boat. One of these errors is due to the flow disturbance induced by the boat-mounted ADCR The other error is due to the lack of flow homogeneity in horizontal layers assumed by the ADCP algorithm to compute orthogonal velocities from the measured radial velocities along the acoustic beams. The first error is investigated by comparing LES results for an undisturbed flow field with LES results for a flow field disturbed by a boat-mounted ADCR The second error is investigated by comparing the velocities beneath the ADCP simulated by LES with virtual ADCP velocities, which are obtained by applying the ADCP algorithm to LES velocities data mined along the path of the acoustic beams of the virtual profiler. The distribution of the Reynolds stresses beneath the ADCP estimated with the ADCP algorithm from the virtual ADCP velocity data are also compared with those obtained from the LES solutions for both the undisturbed and ADCP-disturbed flows. Results show that the boat significantly disturbs the flow field and that the disturbed flow field is qualitatively different from the flow fields observed around an isolated ADCP (no boat). DOI: 10.1061/(ASCE)HY.1943-7900.0000083 CE Database subject headings: Simulation; Computational fluid dynamics technique; Acoustic techniques; Flow measurement; Turbulence; Errors; Uncertainty principles.

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 measurements. In discussing the elemental errors, we look into what determines their uncertainties and whether they can be evaluated using available information. We then apply the guidelines of the AIAA standard to develop an analytical framework for propagating the uncertainties from the elemental sources to obtain the total uncertainty of ADCP discharge measurements from a moving boat. CE Database subject headings: Open channel flow; River flow; Flow measurement; Uncertainty principles; Small crafts; Velocity.

A method for determining the flow carrying capacity of a channel system, capable of accounting for the interacting backwater effect among channel reaches and incoming lateral flow, is presented here. The method makes use of hydraulic performance graphs - a new tool for dealing with open-channel-flow problems. The hydraulic performance graph summarizes all the backwater profile information for a channel reach. As an illustration, the method is applied to evaluate the channel capacities of a portion of Boneyard Creek in the city of Urbana, Ill. The example demonstrates that the channel flow capacity is a function of the exit water level, of which the maximum normal flow capacity and the absolute maximum carrying capacity are special cases.

Accurate flow ratings at water-control structures are essential for water-resource management. This paper presents an approach to obtain numerically generated data using computational fluid dynamics (CFD) to complement field measurements needed to improve spillway flow-rating formulas. The procedure to generate CFD flow data described herein is based on solving Reynolds-Averaged Navier-Stokes equations using the κ-ε turbulence closure model with the free surface resolved by the volume of fluid (VOF) method. The steps for setting the computational domain, generating the mesh, selecting the boundary conditions, and choosing a convergence criteria for the simulations are discussed. The turbulence closure model and VOF method for the present application are verified with data from laboratory measurements of submerged jet flow below a gate and in a sharp open-channel bend. CFD flow data generation is validated with laboratory and field measurements for gated ogee spillways in south Florida. The results presented here demonstrate that CFD is a plausible alternative to complement data measured at prototype structures and reduced-scale models for the purpose of calibration and validation of rating formulas used for real-time flow monitoring at prototype water-control structures. [ABSTRACT FROM AUTHOR]

Large-scale water resources systems are often managed by an integrated set of hydraulic structures that are vulnerable to wider ranges of discharge and tailwater elevation than envisioned in their original design due to climate change and additional project objectives such as fostering healthy ecosystems. The present physical model study explored the performance of a spillway structure on the Kissimmee River, operated by the South Florida Water Management District, under extreme conditions of drought and flooding with accompanying low and high tailwater levels for both gate-controlled and uncontrolled spillway flow conditions. Maximum scour depths and their locations for two different riprap apron lengths downstream of the spillway stilling basin were measured along with the complex flow fields prior to scour. Effects of tailwater submergence, type of spillway flow and riprap apron length on scour results are interpreted in terms of the measured turbulent kinetic energy and velocity distributions near the bed. [ABSTRACT FROM AUTHOR]