Journal of Hydraulic Engineering

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March 2006

Volume 132, Issue 3, pp. 225-342

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Case Study of Precision of GPS Differential Correction Strategies: Influence on aDcp Velocity and Discharge Estimates

Colin D. Rennie and Francois Rainville

J. Hydraul. Eng. 132, 225 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(225) (10 pages) | Cited 8 times

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The precision of four differential global positioning systems (DGPS) was evaluated in the context of fluvial water velocity and discharge measurement. DGPS is used to resolve water velocities measured with an acoustic Doppler current profiler (aDcp) into earth coordinates if bottom tracking is unavailable. The DGPS systems assessed were: (1) the dual frequency real time kinematic (RTKL1L2); (2) the single frequency real time kinematic (RTKL1); (3) the code-phase Canadian Coast Guard (CG); and (4) the code-phase Wide Area Augmentation System (WAAS). Repeat discharge surveys (n = 22) were conducted at a transect of the Gatineau River, Canada, simultaneously collecting bottom track boat velocity (vBT) and boat velocity from all four DGPS (vDGPS). The mean absolute single ping differences between vBT and vDGPS were 3.1 (RTKL1L2), 3.2 (RTKL1), 8.9 (CG), and 9.8 cm/s (WAAS). Errors were observed more often near channel margins, presumably due to obstruction and multipath associated with riverbank vegetation and buildings. DGPS velocity errors were random, and a large number of DGPS positions were utilized across the section to record discharge. Accordingly, errors in discharge were relatively small, with maximum percentage differences between single transect QBT and QDGPS of 0.9 (RTKL1L2), 1.0 (RTKL1), 2.4 (CG), and 3.1% (WAAS). Simulations suggest large discharge errors (up to 51%) are possible under low sampling intensity (20 pings) and small channel velocity relative to average vDGPS error (ratio of 1).

Countermeasure Toe Protection at Spill-Through Abutments

Bruce Melville, M.ASCE, Sjoerd van Ballegooy, Stephen Coleman, and Brian Barkdoll, M.ASCE

J. Hydraul. Eng. 132, 235 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(235) (11 pages) | Cited 6 times

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An experimental study of scour countermeasures for spill-through abutments situated on the flood plain of a compound channel is reported. The purpose of the study was to determine the variations in the scour hole geometry under clear water conditions by varying the compound channel and abutment geometries, and to determine the extent and type of scour countermeasure toe protection provided. This approach avoids one of the inherent difficulties in conducting scour countermeasure experiments—that is, the subjectivity of determining whether the countermeasure used in the experiment is a success or a failure. Riprap and cable-tied block countermeasures are incorporated. The results show that for most cases, as the countermeasure apron width (i.e., the extent of toe protection) is increased, the scour hole is deflected further away from the abutment and reduces in size. However, for abutment and compound channel configurations where the scour hole forms close to the main channel bank, the scour hole increases in size as the apron width is increased. The results also show that cable-tied block mats allow the scour hole to form closer to the abutment than equivalent riprap aprons and result in deeper scour holes. A suggested design methodology for the extent of apron protection is presented. The method is an improvement on the current, rather-simplified practice of providing aprons of fixed width equal to twice the flow depth.

Scour Downstream of an Apron Due to Submerged Horizontal Jets

Subhasish Dey and Arindam Sarkar

J. Hydraul. Eng. 132, 246 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(246) (12 pages) | Cited 12 times

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The results of an experimental investigation on scour of noncohesive sediment beds (uniform and nonuniform sediments) downstream of an apron due to a submerged horizontal jet issuing from a sluice opening are presented. Attempts are made to explain the similarity existing in the scour process and profiles (including dune in the downstream of the scour hole). The scour profiles at different times follow a particular geometrical similarity and can be expressed by the combination of two polynomials. Using experimental scour depth at different times, the time variation of scour depth is scaled by an exponential law, where time scale increases linearly with densimetric Froude number. The equilibrium scour depth, related to the sediment size relative to the sluice opening, decreases with increase in sediment size and sluice opening. On the other hand, the equilibrium scour depth increases with increase in densimetric Froude number. The variation of equilibrium scour depth with tailwater depth indicates a critical tailwater depth corresponding to a minimum equilibrium scour depth. The effect of sediment gradation on scour depth is pronounced for nonuniform sediments, which reduce scour depth significantly due to formation of an armor layer, and therefore prompted study of the reduction of scour depth by a launching apron placed downstream of the rigid apron. The results show that the average reduction of scour depth by placing a launching apron was 39%, having a maximum of 57.3% and a minimum of 16.2%. The characteristic parameters affecting maximum equilibrium scour depth are identified based on the physical reasoning and dimensional analysis. Equation of maximum equilibrium scour depth obtained empirically agrees well with the experimental data.

2D Shallow-Water Model Using Unstructured Finite-Volumes Methods

Dan K. Nguyen, Yu-E Shi, Sam S. Y. Wang, F.ASCE, and The Hung Nguyen

J. Hydraul. Eng. 132, 258 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(258) (12 pages) | Cited 2 times

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This paper presents a two-dimensional (2D) shallow-water numerical model, which is based on the resolution of the Saint–Venant equation using the unstructured finite-volumes method, combined with Green’s theorem technique. The model has been validated by several benchmarks. The numerical results obtained from the model are in good agreement with the analytical or experimental ones. The paper also presents an application of this model to flood diversion from the Red River into a water-retention zone for the purpose of reducing flood threat at Hanoi, capital of Vietnam.

Control of Scour at Vertical Circular Piles under Waves and Current

Subhasish Dey, B. Mutlu Sumer, and Jørgen Fredsøe

J. Hydraul. Eng. 132, 270 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(270) (10 pages) | Cited 5 times

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An experimental study on the control of scour at vertical circular piles under monochromatic waves and a steady current is presented. The experiments on wave and steady currents were carried out under live-bed and clear-water regimes, respectively. In waves, splitter plate attached to the pile along the vertical plane of symmetry and threaded pile (helical wires or cables wrapped spirally on the pile to form threads) were found to be effective to reduce the scour depth. For the Keulegan–Carpenter numbers 6–100, the vortex shedding is the main mechanism of scour under waves. The splitter plate and threaded pile disrupt the vortex shedding. The average reduction of the scour depth by the splitter plate was 61.6%. For threaded piles, different combinations of cable and pile sizes were tested, and the best combination was found for a cable–pile diameter ratio equaling 0.75, in which average scour depth reduction was 51.1%. The average reductions of scour depths for other cable–pile diameter ratios of 0.33 and 0.5 were 43.2 and 48.1%, respectively. On the other hand, in a steady current, the threaded pile proved to be effective to control scour depth to a great extent. Cables wrapped spirally forming threads on the pile help to weaken the downflow and horseshoe vortex, which are the principal agents of scour under a steady current. The experimental results showed that the scour depth consistently decreases with an increase in cable diameter and the number of threads, and with a decrease in thread angle. The maximum reduction of scour depth observed was 46.3% by using a triple threaded pile having a thread angle of 15° and a cable–pile diameter ratio of 0.1. The proposed methods of controlling scour are easy to install and are economical.

Dam Break Wave of Thixotropic Fluid

H. Chanson, S. Jarny, and P. Coussot

J. Hydraul. Eng. 132, 280 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(280) (14 pages) | Cited 11 times

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Thixotropy is the characteristic of a fluid to form a gelled structure over time when it is not subjected to shearing, and to liquefy when agitated. Thixotropic fluids are commonly used in the construction industry (e.g., liquid concrete and drilling fluids), and related applications include some forms of mud flows and debris flows. This paper describes a basic study of dam break wave with thixotropic fluid. Theoretical considerations were developed based upon a kinematic wave approximation of the Saint-Venant equations down a prismatic sloping channel. A very simple thixotropic model, which predicts the basic rheological trends of such fluids, was used. It describes the instantaneous state of fluid structure by a single parameter. The analytical solution of the basic flow motion and rheology equations predicts three basic flow regimes depending upon the fluid properties and flow conditions, including the initial “degree of jamming” of the fluid (related to its time of restructuration at rest). These findings were successfully compared with systematic bentonite suspension experiments. The present work is the first theoretical analysis combining the basic principles of unsteady flow motion with a thixotropic fluid model and systematic laboratory experiments.

Time-Line Interpolation Errors in Pipe Networks

Masashi Shimada, Jim Brown, Della Leslie, and Alan Vardy, F.ASCE

J. Hydraul. Eng. 132, 294 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(294) (13 pages) | Cited 3 times

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An exact method of assessing numerical errors in analyses of unsteady flows in pipe networks is introduced. The assessment is valid for fixed-grid method of characteristics analyses using time-line interpolations. A pipe polynomial transfer matrix is developed and is analogous to transfer function matrices used in free oscillation theory. The influence of reachback is assessed by comparing exact numerical predictions using a polynomial transfer matrix with exact analytical predictions obtained using free oscillation theory. The investigation is part of a long-term project aimed at automating the selection of numerical grid sizes in unsteady flow analyses. The eventual goal is to enable users of unsteady flow software to prescribe required degrees of accuracy instead of specifying the numerical grid itself. This paper is only a first step toward the long-term aim, but it is a big step toward an intermediate objective of providing exact benchmarking data for the assessment of approximate methods of automatic grid selection.

Three-Dimensional Topography of Debris-Flow Fan

Yuan-Fan Tsai

J. Hydraul. Eng. 132, 307 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(307) (12 pages) | Cited 2 times

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Study on debris-flow fan configurations lays the groundwork for hazard zone mappings of debris flow disasters. This paper aims to identify the morphological similarity of debris-flow fans based on a series of laboratory experiments and field investigations. The maximum length Lc, width Bm, and thickness Zo of debris-flow fans are adopted as the characteristic parameters in the analysis of morphological similarity of debris-flow fans. This analysis demonstrates that the nondimensional longitudinal and transverse profiles of debris-flow fans can be described by Gaussian curves, while a circular curve can be used to fit the nondimensional plan form of the debris-flow fans. By combining the three nondimensional curves mentioned above, the volume ∀ of a debris-flow fan can be related to the maximum length Lc, maximum width Bm, and maximum thickness Z0 by ∀ = αLcBmZo, via an empirical coefficient α. The parameter α is approximately 0.275 for a natural stony debris-flow fan and greater than 0.275 for a natural mud debris-flow fan. In addition, the three-dimensional topography of debris-flow fans can be easily derived based on the parameters Lc, Bm, and Zo using three morphological similarity formulae.
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Bridge Blockage and Overbank Flow Simulations Using HEC–RAS in the Keelung River during the 2001 Nari Typhoon

Kwan Tun Lee, Yao-Hsien Ho, and Yuh-Ju Chyan

J. Hydraul. Eng. 132, 319 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(319) (5 pages) | Cited 4 times

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On September 16, 2001, Typhoon Nari resulted in severe flooding in the Keelung River basin. More than 1,000 shipping containers were swept by the rising water from the floodplain into the river, blocking 14 bridges. A severe overbank flow due to the blockage occurred at the Ba-Tu Railway Bridge. The overbank flow then passed through a railway tunnel and inundated Keelung City, resulting in significant damage. The objective of this study was to determine the influence of the bridge blockage and the Ba-Tu overbank flow on the water stages in the Keelung River during Typhoon Nari. The floating-pier-debris module and the lateral-weir module in the Hydrologic Engineering Center–River Analysis System (HEC-RAS) unsteady-flow routing model were applied to investigate water stage variation due to the bridge blockage and overbank flow. The numerical simulation results provided by this study served as an important reference for authorities who needed to clarify the responsibility of the containers’ owners for the loss of lives and property during this typhoon.

Flow-Induced Failure of Cable-Tied Blocks

Bruce Melville, M.ASCE, Rick van Ballegooy, and Sjoerd van Ballegooy

J. Hydraul. Eng. 132, 324 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(324) (4 pages) | Cited 1 time

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An experimental study of flow-induced failure of cable-tied blocks is presented. The particular failure mechanism studied is overturning and rolling up of the leading edge of a cable-tied block mat. Individual blocks were investigated also. The block size, flow depth, and block (mat) protrusion above the surrounding bed were systematically varied. The results are presented in terms of the critical dimensionless shear stress θc for block (mat) failure. A relationship between θc, block size and block protrusion, and flow depth is given.
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Review of Wastewater Collection System Modeling and Design by T. M. Walski, T. E. Barnard, E. Harold, L. B. Merrit, N. Walker, and B. E. Whitman

Jacques W. Delleur, Reviewer

J. Hydraul. Eng. 132, 328 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(328) (2 pages)

Online Publication Date: 15 February 2006

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Papers of Interest

J. Hydraul. Eng. 132, 330 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(330) (2 pages)

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Discussion of “Efficient Algorithm for Computing Einstein Integrals” by Junke Guo and Pierre Y. Julien

Jorge D. Abad and Marcelo H. García

J. Hydraul. Eng. 132, 332 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(332) (3 pages) | Cited 2 times

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Discussion of “Efficient Algorithm for Computing Einstein Integrals” by Junke Guo and Pierre Y. Julien

A. Roland and U. Zanke

J. Hydraul. Eng. 132, 334 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(334) (3 pages)

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Closure to “Efficient Algorithm for Computing Einstein Integrals” by Junke Guo and Pierre Y. Julien

Junke Guo and Pierre Y. Julien

J. Hydraul. Eng. 132, 337 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(337) (3 pages)

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Discussion of “Simulation of Flow and Mass Dispersion in Meandering Channels” by Jennifer G. Duan

Chyan-Deng Jan, Ji-Shang Wang, and Tsung-Hsien Chen

J. Hydraul. Eng. 132, 339 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(339) (2 pages) | Cited 2 times

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Closure to “Simulation of Flow and Mass Dispersion in Meandering Channels” by Jennifer G. Duan

Jennifer G. Duan

J. Hydraul. Eng. 132, 341 (2006); http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(341) (1 page) | Cited 1 time

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