Journal of Hydraulic Engineering

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December 2007

Volume 133, Issue 12, pp. 1297-1440

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Acoustic Velocimetry for Riverine Environments

Marian Muste, Tracy Vermeyen, Rollin Hotchkiss, and Kevin Oberg

J. Hydraul. Eng. 133, 1297 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1297) (2 pages) | Cited 3 times

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Comparison of Fixed- and Moving-Vessel Flow Measurements with an aDp in a Large River

Ricardo N. Szupiany, Mario L. Amsler, James L. Best, and Daniel R. Parsons

J. Hydraul. Eng. 133, 1299 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1299) (11 pages) | Cited 18 times

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A comparison of three-dimensional flow velocity measurements, made with an acoustic Doppler profiler (aDp) from fixed and moving vessels at cross sections of the Paraná River, Argentina, was performed. The purpose was to design a rapid and reliable procedure for quantifying the velocity field, and related parameters such as bed shear velocity and the identification of secondary circulations, in large rivers using an aDp. The fixed-vessel measurements were performed over a period of 10 min at three vertical profiles along two of the sections. These data were then compared with the results of ten moving-vessel repeat transects made at each of the sections, and which intersected the fixed-vessel sampling locations, using a number of different aDp setup configurations. From the velocity profiles obtained with both fixed- and moving-vessel measurements, total bed shear velocity values were computed by applying the law-of-the-wall. The results indicate there can be significant differences between velocities obtained using the moving-vessel method and fixed-vessel measurements averaged over 10 min. These differences in horizontal velocity can be significantly reduced by averaging five, or more, moving-vessel transects, with corresponding shear velocities calculated from five-transect averages showing differences ranging between 10 and 15%, dependent on the aDp configuration. Location of the at-a-point vertical velocity profile in relation to large-scale bed roughness may also be an influential factor, and ideally the bed morphology should be quantified together with the aDp-derived velocities. When using the aDp to identify secondary flow cells, it was found that although one cross-section transect can provide a reasonable overall picture, an average of five cross sections is necessary to resolve the finer details of flow. The implications for applications that use moving-vessel techniques for measurement and analysis of three-dimensional flow structures, including secondary flows, are highlighted.

Evaluation of Mean Velocity and Turbulence Measurements with ADCPs

Elizabeth A. Nystrom, Chris R. Rehmann, M.ASCE, and Kevin A. Oberg

J. Hydraul. Eng. 133, 1310 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1310) (9 pages) | Cited 4 times

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To test the ability of acoustic Doppler current profilers (ADCPs) to measure turbulence, profiles measured with two pulse-to-pulse coherent ADCPs in a laboratory flume were compared to profiles measured with an acoustic Doppler velocimeter, and time series measured in the acoustic beam of the ADCPs were examined. A four-beam ADCP was used at a downstream station, while a three-beam ADCP was used at a downstream station and an upstream station. At the downstream station, where the turbulence intensity was low, both ADCPs reproduced the mean velocity profile well away from the flume boundaries; errors near the boundaries were due to transducer ringing, flow disturbance, and sidelobe interference. At the upstream station, where the turbulence intensity was higher, errors in the mean velocity were large. The four-beam ADCP measured the Reynolds stress profile accurately away from the bottom boundary, and these measurements can be used to estimate shear velocity. Estimates of Reynolds stress with a three-beam ADCP and turbulent kinetic energy with both ADCPs cannot be computed without further assumptions, and they are affected by flow inhomogeneity. Neither ADCP measured integral time scales to within 60%.

Field Assessment of Alternative Bed-Load Transport Estimators

D. Gaeuman and R. B. Jacobson

J. Hydraul. Eng. 133, 1319 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1319) (10 pages) | Cited 6 times

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Measurement of near-bed sediment velocities with acoustic Doppler current profilers (ADCPs) is an emerging approach for quantifying bed-load sediment fluxes in rivers. Previous investigations of the technique have relied on conventional physical bed-load sampling to provide reference transport information with which to validate the ADCP measurements. However, physical samples are subject to substantial errors, especially under field conditions in which surrogate methods are most needed. Comparisons between ADCP bed velocity measurements with bed-load transport rates estimated from bed-form migration rates in the lower Missouri River show a strong correlation between the two surrogate measures over a wide range of mild to moderately intense sediment transporting conditions. The correlation between the ADCP measurements and physical bed-load samples is comparatively poor, suggesting that physical bed-load sampling is ineffective for ground-truthing alternative techniques in large sand-bed rivers. Bed velocities measured in this study became more variable with increasing bed-form wavelength at higher shear stresses. Under these conditions, bed-form dimensions greatly exceed the region of the bed ensonified by the ADCP, and the magnitude of the acoustic measurements depends on instrument location with respect to bed-form crests and troughs. Alternative algorithms for estimating bed-load transport from paired longitudinal profiles of bed topography were evaluated. An algorithm based on the routing of local erosion and deposition volumes that eliminates the need to identify individual bed forms was found to give results similar to those of more conventional dune-tracking methods. This method is particularly useful in cases where complex bed-form morphology makes delineation of individual bed forms difficult.

Correcting Acoustic Doppler Current Profiler Discharge Measurements Biased by Sediment Transport

David S. Mueller, M.ASCE, P.E. and Chad R. Wagner, A.M.ASCE, P.E.

J. Hydraul. Eng. 133, 1329 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1329) (8 pages) | Cited 1 time

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A negative bias in discharge measurements made with an acoustic Doppler current profiler (ADCP) is attributed to the movement of sediment on or near the streambed, and is an issue widely acknowledged by the scientific community. The integration of a differentially corrected global positioning system (DGPS) to track the movement of the ADCP can be used to avoid the systematic bias associated with a moving bed. DGPS, however, cannot provide consistently accurate positions because of multipath errors and satellite signal reception problems on waterways with dense tree canopy along the banks, in deep valleys or canyons, and near bridges. An alternative method of correcting for the moving-bed bias, based on the closure error resulting from a two-way crossing of the river, is presented. The uncertainty in the mean moving-bed velocity measured by the loop method is shown to be approximately 0.6 cm/s. For the 13 field measurements presented, the loop method resulted in corrected discharges that were within 5% of discharges measured utilizing DGPS to compensate for moving-bed conditions.

Improved Estimation of ADCP Apparent Bed-Load Velocity Using a Real-Time Kalman Filter

C. D. Rennie, F. Rainville, and S. Kashyap

J. Hydraul. Eng. 133, 1337 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1337) (8 pages) | Cited 4 times

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An estimate of apparent bed-load velocity (v) can be derived from the difference between differential global positioning system (DGPSs) and acoustic Doppler current profiler (ADCP) bottom track (BT) measurements when BT is biased by a moving bottom. A Kalman filter has been developed to integrate GPS and bottom track data to improve estimation of boat velocity during ADCP measurements under moving bed conditions (Rennie and Rainville, 2008, J. Hydraulic Eng., in review). The boat velocity estimated using the Kalman filter is superior to boat velocity from raw GPS data. In this paper we assess the improvement in estimation of v using the Kalman filter as opposed to raw GPS data. Specifically, a synthetic moving bed bias was generated for 22 repeat transects of the Gatineau River, Quebec. The synthetic moving bed bias had mean, variance, and distribution across the section as typically observed during bed-load transport conditions, and had the advantage that it was known explicitly. The errors in estimated apparent bed-load velocity derived using either raw DGPS data or the Kalman filter boat velocity were compared. It was found that the improved boat velocity from the Kalman filter yielded significantly (α = 0.05) better estimates of v, (e.g., 61% reduction in error when the Kalman filter boat velocity was used instead of wide area augmentation system GGA), because boat velocity errors were reduced. Tests with real moving bed data confirmed the Kalman filter was able to significantly reduce errors in bed load calculated with stand alone GPS.

Flow Measurement Using Flying ADV Probes

Thomas MacDougal Clunie, Vladimir I. Nikora, Stephen E. Coleman, Heide Friedrich, and Bruce W. Melville

J. Hydraul. Eng. 133, 1345 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1345) (11 pages) | Cited 2 times

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An innovative measurement system of “flying” acoustic Doppler velocimeters was designed in order to allow rapid velocity measurement over a large flow field. Such measurements are necessary, for example, when measuring over a temporally varying and locally nonuniform rough bed. The measurement technique was verified by comparison with measurements taken in the same flows using a traditional stationary probe technique. Comparison showed that the flying-probe approach performs similarly to stationary measurements in capturing the mean flow field and turbulent fluctuations. The data obtained from flying probe experiments can be used to describe the flow in terms of double-averaged hydrodynamic variables, obtained by averaging in time and spatial domains within a thin slab parallel to the mean bed. Examples are presented of flow measurements over a fixed flat bed, a fixed dune bed, and over mobile developing bed forms. It is shown that near-bed measurements suffer from boundary reflection interference, though affected data can be filtered out based on the ADV-measured correlation coefficient. Measurement below roughness tops is possible, with in-bed records being detectable by spikes in measured signal-to-noise-ratio and by comparison with measured bed topography.

ADCP Measurements of Gravity Currents in the Chicago River, Illinois

Carlos M. García, Kevin Oberg, and Marcelo H. García

J. Hydraul. Eng. 133, 1356 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1356) (11 pages) | Cited 3 times

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A unique set of observations of stratified flow phenomena in the Chicago River was made using an upward-looking acoustic Doppler current profiler (ADCP) during the period November 20, 2003 to February 1, 2004. Water density differences between the Chicago River and its North Branch (NB) seem to be responsible for the development of gravity currents. With the objective of characterizing the occurrence, frequency, and evolution of such currents, the ADCP was configured to continuously collect high-resolution water velocity and echo intensity profiles in the Chicago River at Columbus Drive. During the observation period, 28 gravity current events were identified, lasting a total of 77% of the time. Sixteen of these events were generated by underflows from the NB and 12 of these events were generated by overflows from the NB. On average, the duration of the underflow and overflow events was 52.3 and 42.1 h, respectively. A detailed analysis of one underflow event, which started on January 7, 2004, and lasted about 65 h, was performed. This is the first time that ADCP technology has been used to continuously monitor gravity currents in a river.

Turbulence Descriptions in Two Cobble-Bed River Reaches

Mark C. Stone, M.ASCE and Rollin H. Hotchkiss, M.ASCE, P.E.

J. Hydraul. Eng. 133, 1367 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1367) (12 pages) | Cited 5 times

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The hydrodynamic flow field in streams and rivers influences many ecological processes including organism dispersal, habitat use, and resource acquisition. Understanding the linkages between hydrodynamic and ecological processes is essential for developing effective restoration and management tools. Despite the pervasive influence of flow velocity and turbulence, the details of natural stream flow fields as they apply to ecological concepts are poorly understood. In this study, velocity and turbulence distributions were investigated at two spatial scales using an acoustic Doppler velocimeter. The measurements were collected in two cobble-bed rivers with mean depths of approximately 0.5 m, relative roughness values between 0.12 and 0.33, and streamflow rates of 1.5 and 3.1 m3/s. The analysis included mean velocity, Reynolds shear stress (τR), turbulence intensity (TI), and turbulent kinetic energy (TKE) vertical profiles and horizontal heterogeneity collected in riffle, run, and pool habitat units. The measured profiles were compared with previously reported semiempirical equations. The logarithmic profile reasonably described the vertical velocity profiles. However, the observed TI, TKE, and τR profiles deviated noticeably from the semiempirical relationships. Velocity magnitude and cross-correlation coefficients revealed strong spatial heterogeneity at both the reach and fine scales. Spatial heterogeneity was also observed in TI and TKE data, but to a lesser degree. The results provide a novel description of flow field characteristics in cobble-bed rivers while demonstrating techniques for measuring velocity and turbulence distributions in natural streams in the context of an ecohydraulics study.

ADV Measurements around a Cluster Microform in a Shallow Mountain Stream

Kyle B. Strom and Athanasios N. Papanicolaou

J. Hydraul. Eng. 133, 1379 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1379) (11 pages) | Cited 8 times

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A field study was conducted to examine the turbulent properties of the flow around a naturally formed cluster bedform. This was carried out on a mountain river using a 3D acoustic Doppler velocimeter (ADV). Concurrent with this objective, the ability of the ADV to make measurements in a shallow flow over a cobble bed (ho/d84 = 1.75) was examined. ADV measurements in natural clear-water shallow flows around obstacles are inherently difficult to obtain due to (1) signal interference between the acoustic reflections from the boundary and the ADV sample volume; (2) regions of high turbulent intensity, such as in local detached shear layers; and (3) low concentrations of suspended particles passing through the ADV sampling volume. These processes result in velocity time series that contain a significant amount of spikes, lower-than-average signal-to-noise ratios, and lower than average correlation values. A filtering process that optimized the removal of bad points while retaining a sufficient number of points to describe the velocity time series histogram was developed. In general, flow over the study section can be described by an inner roughness layer dominated by large roughness and detached flow, and an outer flow that exhibits a form of log scaling. It was found that the cluster acts to locally modify this structure by shifting the elevation of the roughness layer and the zone of primary production and dissipation of turbulent energy up towards the center of the water column. Mean and turbulent statistics, energy distributions, spectral properties, and a quadrant analysis are presented to characterize the flow around the cluster.

Framework for Estimating Uncertainty of ADCP Measurements from a Moving Boat by Standardized Uncertainty Analysis

Juan A. González-Castro, A.M.ASCE and Marian Muste, A.M.ASCE

J. Hydraul. Eng. 133, 1390 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1390) (21 pages) | Cited 13 times

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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.

Errors in Acoustic Doppler Profiler Velocity Measurements Caused by Flow Disturbance

David S. Mueller, Jorge D. Abad, Carlos M. García, Jeffery W. Gartner, Marcelo H. García, and Kevin A. Oberg

J. Hydraul. Eng. 133, 1411 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1411) (10 pages) | Cited 10 times

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Acoustic Doppler current profilers (ADCPs) are commonly used to measure streamflow and water velocities in rivers and streams. This paper presents laboratory, field, and numerical model evidence of errors in ADCP measurements caused by flow disturbance. A state-of-the-art three-dimensional computational fluid dynamic model is validated with and used to complement field and laboratory observations of flow disturbance and its effect on measured velocities. Results show that near the instrument, flow velocities measured by the ADCP are neither the undisturbed stream velocity nor the velocity of the flow field around the ADCP. The velocities measured by the ADCP are biased low due to the downward flow near the upstream face of the ADCP and upward recovering flow in the path of downstream transducer, which violate the flow homogeneity assumption used to transform beam velocities into Cartesian velocity components. The magnitude of the bias is dependent on the deployment configuration, the diameter of the instrument, and the approach velocity, and was observed to range from more than 25% at 5 cm from the transducers to less than 1% at about 50 cm from the transducers for the scenarios simulated.

Validation of Streamflow Measurements Made with Acoustic Doppler Current Profilers

Kevin Oberg and David S. Mueller, M.ASCE

J. Hydraul. Eng. 133, 1421 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1421) (12 pages) | Cited 11 times

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The U.S. Geological Survey and other international agencies have collaborated to conduct laboratory and field validations of acoustic Doppler current profiler (ADCP) measurements of streamflow. Laboratory validations made in a large towing basin show that the mean differences between tow cart velocity and ADCP bottom-track and water-track velocities were −0.51 and −1.10%, respectively. Field validations of commercially available ADCPs were conducted by comparing streamflow measurements made with ADCPs to reference streamflow measurements obtained from concurrent mechanical current-meter measurements, stable rating curves, salt-dilution measurements, or acoustic velocity meters. Data from 1,032 transects, comprising 100 discharge measurements, were analyzed from 22 sites in the United States, Canada, Sweden, and The Netherlands. Results of these analyses show that broadband ADCP streamflow measurements are unbiased when compared to the reference discharges regardless of the water mode used for making the measurement. Measurement duration is more important than the number of transects for reducing the uncertainty of the ADCP streamflow measurement.
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Application of Acoustic Doppler Velocimeters for Streamflow Measurements

Michael Rehmel

J. Hydraul. Eng. 133, 1433 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1433) (6 pages) | Cited 2 times

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The U.S. Geological Survey (USGS) principally has used Price AA and Price pygmy mechanical current meters for measurement of discharge. New technologies have resulted in the introduction of alternatives to the Price meters. One alternative, the FlowTracker acoustic Doppler velocimeter, was designed by SonTek/YSI to make streamflow measurements in wadeable conditions. The device measures a point velocity and can be used with standard midsection method algorithms to compute streamflow. The USGS collected 55 quality-assurance measurements with the FlowTracker at 43 different USGS streamflow-gaging stations across the United States, with mean depths from 0.05 to 0.67 m, mean velocities from 13 to 60 cm/s, and discharges from 0.02 to 12.4 m3/s. These measurements were compared with Price mechanical current meter measurements. Analysis of the comparisons shows that the FlowTracker discharges were not statistically different from the Price meter discharges at a 95% confidence level.
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Call for Collaboration in WMO Project for the Assessment of the Performance of Flow Measurement Instruments and Techniques

Janice M. Fulford, Paul J. Pilon, Zurab Kopaliani, Patrick J. McCurry, and Claudio Caponi

J. Hydraul. Eng. 133, 1439 (2007); http://dx.doi.org/10.1061/(ASCE)0733-9429(2007)133:12(1439) (2 pages)

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