Journal of Hydraulic Engineering

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December 2004

Volume 130, Issue 12, pp. 1135-1223

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Annual Review 2004

Pierre Julien

J. Hydraul. Eng. 130, 1135 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1135) (2 pages)

Online Publication Date: 15 November 2004

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Marine Wastewater Discharges from Multiport Diffusers. I: Unstratified Stationary Water

Xiaodong Tian, A.M.ASCE, Philip J. W. Roberts, F.ASCE, and Gregory J. Daviero, A.M.ASCE

J. Hydraul. Eng. 130, 1137 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1137) (10 pages) | Cited 16 times

Online Publication Date: 15 November 2004

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Laboratory experiments on the near-field mixing of buoyant plumes discharged from multiport diffusers into unstratified stationary water are reported. Dilution was measured by a newly developed three-dimensional laser-induced fluorescence system and a microconductivity probe. Significant additional mixing (and dilution) occurs beyond the point where the plume impacts the water surface. This mixing ceases when the turbulence generated by the plumes collapses in the surface spreading layer. The port spacing, s, was varied through a range encompassing line to point source conditions. In all cases, the concentration distribution in the surface layer eventually becomes laterally uniform. Measurements of the near-field dilution, length, and layer thickness, and semiempirical equations to predict them are presented. The discharge behaves as a line plume when s/H ⩽ 0.3, and as a point plume when s/H ≥ 1.0. The additional near-field mixing for a point plume is much greater than for a line plume. Basing diffuser design on near-field dilution rather than impact-point dilution allows the use of far fewer ports, or risers, with considerable potential cost savings, particularly for tunneled outfalls.

Marine Wastewater Discharges from Multiport Diffusers. II: Unstratified Flowing Water

Xiaodong Tian, A.M.ASCE, Philip J. W. Roberts, F.ASCE, and Gregory J. Daviero, A.M.ASCE

J. Hydraul. Eng. 130, 1147 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1147) (9 pages) | Cited 12 times

Online Publication Date: 15 November 2004

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Laboratory experiments on the near-field mixing of buoyant plumes discharged from multiport diffusers into unstratified flowing water are reported. The spatial variation of dilution was measured by a newly developed three-dimensional laser-induced fluorescence system and a microconductivity probe. The near-field hydrodynamics are complex. The plumes discharged upstream dilute and merge more rapidly than those discharged downstream. Even with wide port spacing, the plumes eventually merge to form a laterally uniform surface wastefield. The density profile in this wastefield becomes gravitationally stable and suppresses mixing, marking the end of the near field. The value of the port spacing ratio, s/H, below which the discharge approximates a line plume is greater for discharge into a flowing current than into a stationary environment, so the port spacing plays a lesser role in a flowing current. The mixing and dilution that occurs in the surface layer is less than for a discharge into a stationary environment, and it decreases as the current speed increases. Semiempirical equations to predict the major near field characteristics are presented.

Experiments on Selective Withdrawal of a Codirectional Two-Layer Flow through a Line Sink

Wei-Sheng Yu, Shaohua Marko Hsu, P.E., M.ASCE, and Kan-Long Fan

J. Hydraul. Eng. 130, 1156 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1156) (11 pages) | Cited 1 time

Online Publication Date: 15 November 2004

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For investigating selective withdrawal problems, laboratory experiments were conducted in a horizontal flume with a co-directional two-layer flow of different density into a line sink. Saline water was used as the fluid of the lower layer instead of sediment-laden turbid water for achieving a steady state. In this study, a trend curve was produced using the data of many runs which were taken under varying conditions from aspiration of both layers to only lower-layer aspiration. An adequate parameter for determining the critical condition was obtained from this trend curve. The critical condition is defined as the beginning or ending of aspiration for the upper layer. Suitable variables for the parameter are also discussed. A theoretical formula is suggested and verified, which is better than a traditional empirical formula for calculating the withdrawal concentration. Effects of slot elevation on the lower layer flow and the thickness of the mixing layer are also discussed.

Simulation of Transcritical Flow in Pipe/Channel Networks

Slobodan Djordjević, Dušan Prodanović, and Godfrey A. Walters

J. Hydraul. Eng. 130, 1167 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1167) (12 pages) | Cited 5 times

Online Publication Date: 15 November 2004

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Using finite difference methods in conjunction with the reduced momentum equation and applying boundary condition structure inherent to subcritical flow to all regimes, is an approach that enables efficient numerical simulation of supercritical and transcritical flows in pipe/channel systems. However, as well as certain errors within a single channel due to incomplete equations, this technique also may introduce unwanted effects propagating across a network in both upstream and downstream directions. These may include: unrealistic backwater effects due to improper boundary conditions, nonamplifying oscillations due to jerky jump movement, and other computational instabilities. Practical implications of these are analyzed in detail and are illustrated using a set of examples. Sensitivity analyzes and comparisons with analytical solutions and laboratory experiments are made. The measures to reduce the inaccuracies inevitable in simulation of transcritical flows are discussed.

Velocity Distribution and Dip-Phenomenon in Smooth Uniform Open Channel Flows

Shu-Qing Yang, Soon-Keat Tan, and Siow-Yong Lim

J. Hydraul. Eng. 130, 1179 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1179) (8 pages) | Cited 24 times

Online Publication Date: 15 November 2004

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This paper investigates the mechanism of the dip phenomenon whereby the location of the maximum velocity appears below the free surface vis-à-vis the secondary currents in open-channel flows. It is found that the classical log law gives a good description of the velocity distribution in the inner region if the local shear velocity is introduced into the dimensionless distance, i.e., u*(z)y/ν. In the outer region, where the maximum velocity occurs at some distance below the free surface in a vertical plane, it is found that the velocity deviation from the log law is linearly proportional to the logarithmic distance ln(1−y/h) from the free surface. To this end, the study proposes a dip-modified log law for the velocity distribution in smooth uniform open channel flows. This new law is capable of describing the dip phenomenon, and is applicable to the velocity profile in the region from the near bed to just below the free surface, and transversely, from the center line to the near-wall region of the channel. The dip-modified log law consists of two logarithmic distances, one from the bed ln(u*(z) y/ν), and the other from the free surface ln(1−y/h), respectively, and a dip-correction factor α. The latter is the only parameter that needs to be determined and an empirical equation for α has been proposed in this study. The dip-modified log law has been verified using published experimental data for smooth rectangular open channels and the agreement between the measured and computed velocity profiles is good.

Entrainment Probabilities of Mixed-Size Sediment Incorporating Near-Bed Coherent Flow Structures

Fu-Chun Wu and Kuo-Hsin Yang

J. Hydraul. Eng. 130, 1187 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1187) (11 pages) | Cited 14 times

Online Publication Date: 15 November 2004

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In this work we incorporate the effect of near-bed coherent flow structures into the entrainment of randomly configured mixed-size sediments. The fourth-order Gram–Charlier type probability density function (GC pdf) of near-bed streamwise velocity is employed to account for the higher-order correlations associated with turbulent bursting. A compilation of the published data over a wide range of bed roughness is used to analyze the near-bed coherent flow structures, including the second-, third-, and fourth-order moments of velocity fluctuation (i.e., turbulence intensity, skewness, and flatness factors) required in the fourth-order GC pdf. An important result of this study is a set of quantitative relations used to predict these higher-order moments as a function of the roughness Reynolds number. The random grain protrusion is parameterized with the exposure and friction heights, and an existing probabilistic approach is used to correct the hiding effect of mixed-size sediment. The above factors are all incorporated into the formulation of entrainment (rolling and lifting) probabilities. As compared to the previous normal and lognormal models, the present results demonstrate significantly improved agreement with the observed data for the unisize and mixed-size sediments under partial- and full-transport conditions. The results also reveal that the third-order GC pdf can be used to approximate the fourth-order one for the fully rough beds, however, for smooth beds the fourth-order GC pdf should be used to adequately incorporate the effects of higher-order correlations. This paper offers some new insights into the processes of sediment entrainment.
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Efficient Algorithm for Computing Einstein Integrals

Junke Guo and Pierre Y. Julien

J. Hydraul. Eng. 130, 1198 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1198) (4 pages) | Cited 1 time

Online Publication Date: 15 November 2004

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Analytical approximations to Einstein integrals are proposed. The approximations represented by two fast-converging series are valid for all values of their arguments. Accordingly, the algorithm can be easily incorporated into professional software like HEC-RAS or HEC-6 with minimum computational effort.

Superior Exploration–Exploitation Balance in Shuffled Complex Evolution

Nitin Muttil and Shie-Yui Liong

J. Hydraul. Eng. 130, 1202 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1202) (4 pages) | Cited 7 times

Online Publication Date: 15 November 2004

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Numerous applications within water resources require a robust and efficient optimization algorithm. Given that these applications involve multimodal nonconvex and discontinuous search spaces, evolutionary algorithms (EAs)—which are known to possess global optimization properties—have been widely used for this purpose. For an evolutionary algorithm to be successful, two important facets of the search—exploration and exploitation of the search space—need to be addressed. In this study, we address the issue of achieving a superior exploration–exploitation tradeoff in an extensively used EA, the shuffled complex evolution (SCE-UA). A scheme to improve the exploration capability of the SCE-UA in finding the global optimum is suggested. The scheme proposed a systematically located initial population instead of a randomly generated one used in SCE-UA. On a suite of commonly used test functions, the robustness and efficiency of the modified SCE-UA algorithm was compared with the original SCE-UA. It is observed that when the points in the initial population are strategically placed, it leads to better exploration of the search space, and hence, yields a superior balance between exploration and exploitation. This in turn results in a significant improvement in the robustness of the SCE-UA algorithm.

Salinity-Induced Density Stratification in Near-Laminar Open-Channel Flows

Bernhard H. Schmid, M.ASCE, Michael A. Hengl, and Ursula Stephan

J. Hydraul. Eng. 130, 1206 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1206) (5 pages)

Online Publication Date: 15 November 2004

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Salt tracer experiments are a cost-effective tool widely used in studies of flow and transport in free surface flows. Whereas in a large majority of rivers and streams, fully turbulent conditions achieve rapid vertical mixing of injected tracers, this is not necessarily the case with very low Reynolds number flows as encountered e.g., in wetland ponds. There, often laminar to near-laminar transitional flow regimes prevail, and the fact that solutions of elevated salinity are distinctly heavier than water may result in the development of stable density layers, trapping part of the salt tracer and distorting the breakthrough curve recorded at the outlet. In this study, the conditions under which density stratification develops due to salt injection are analyzed, and a criterion is presented which permits an intended salt tracer experiment to be judged at the planning stage already.
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Discussion of “Design Method of Time-Dependent Local Scour at Circular Bridge Pier” by Md. Faruque Mia and Hiroshi Nago

Giuseppe Oliveto, Jens Unger, and Willi H. Hager, F.ASCE

J. Hydraul. Eng. 130, 1211 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1211) (3 pages) | Cited 2 times

Online Publication Date: 15 November 2004

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Closure to “Design Method of Time-Dependent Local Scour at Circular Bridge Pier” by Md. Faruque Mia and Hiroshi Nago

Md. Faruque Mia and Hiroshi Nago

J. Hydraul. Eng. 130, 1213 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1213) (1 page)

Online Publication Date: 15 November 2004

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Discussion of “Explicit Estimation of Aquifer Diffusivity from Linear Stream Stage” by Sushil K. Singh

Rajesh Srivastava

J. Hydraul. Eng. 130, 1213 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1213.2) (2 pages) | Cited 2 times

Online Publication Date: 15 November 2004

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Closure to “Explicit Estimation of Aquifer Diffusivity from Linear Stream Stage” by Sushil K. Singh

Sushil K. Singh

J. Hydraul. Eng. 130, 1214 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1214) (2 pages)

Online Publication Date: 15 November 2004

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Review of Sedimentation and Sediment Transport by Albert Gyr and Wolfgang Kinzelbach

Pierre Y. Julien, Reviewer

J. Hydraul. Eng. 130, 1216 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1216) (1 page)

Online Publication Date: 15 November 2004

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Reviewers

J. Hydraul. Eng. 130, 1217 (2004); http://dx.doi.org/10.1061/(ASCE)0733-9429(2004)130:12(1217) (7 pages)

Online Publication Date: 15 November 2004

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