Journal of Hydraulic Engineering

An unstructured hybrid mesh numerical method is developed to simulate open channel flows. The method is applicable to arbitrarily shaped mesh cells and offers a framework to unify many mesh topologies into a single formulation. A finite-volume discretization is applied to the two-dimensional depth-averaged equations such that mass conservation is satisfied both locally and globally. An automatic wetting-drying procedure is incorporated in conjunction with a segregated solution procedure that chooses the water surface elevation as the main variable. The method is applicable to both steady and unsteady flows and covers the entire flow range: subcritical, transcritical, and supercritical. The proposed numerical method is well suited to natural river flows with a combination of main channels, side channels, bars, floodplains, and in-stream structures. Technical details of the method are presented, verification studies are performed using a number of simple flows, and a practical natural river is modeled to illustrate issues of calibration and validation.

The paper investigates the influence of the resistance coefficient variability onto the spatial development of roll-waves. Two models, based on time-asymptotic solutions of the linearized St. Venant equations, subject to either impulsive or oscillating perturbation, have been modified by including the dependence of the resistance coefficient on flow conditions, wall roughness, and fluid viscosity. Independently of the perturbation type, it has been shown that the hypothesis of constant resistance coefficient leads to underestimate the disturbance spatial growth. Theoretical predictions are finally compared with results of a fully nonlinear model and with literature experimental data for several combinations of Froude and Reynolds numbers and relative roughness values. The representation of variability of the resistance coefficient fundamentally improves the performance of minimum channel length criteria, whereas its neglect may lead to noncautious channel design.

In this paper, unsteady water quality modeling and the associated sensitivity equations are solved for water distribution systems. A new solution algorithm is proposed, designed for slow varying velocity and based on a time splitting method to separate and solve efficiently each phenomenon such as advection and chemical reaction. This numerical approach allows simultaneous solution of both the direct problem and the sensitivity equations. Special attention is given to the treatment of advection, which is handled with a total variation diminishing scheme. The general model presented in this study permits global sensitivity analysis of the system to be performed and its efficiency is illustrated on two pipe networks. The importance of the sensitivity analysis is shown as part of the calibration process on a real network.

This technical note describes use of a multibeam echosounder (MBES) to quantify the dynamics of suspended sediment in a large open channel. A methodology is detailed that uses the backscatter magnitude from the MBES water-column data to adjust the magnitude of sonar returns for the various sonar settings, spatially and temporally average the data to account for the random nature of acoustic backscatter from the suspended sediment, and calibrate the processed data with direct samples. A case study of flow at the confluence of the Rio Paraná and Rio Paraguay, Argentina, where there is a distinct turbidity difference along the mixing interface of the two flows, is used to demonstrate the unique capabilities of MBES to quantify sediment concentrations and dynamics within the water column.

Energy losses occurring in pipe junctions have been studied for many years. Head loss coefficients $\left(K\right)$ are commonly used to characterize losses across elbows, tees, crosses, valves, and other pipe fittings. When accurate values of $K$ are used, the flow rate and corresponding total head at any location in a pipe network can be calculated. While $K$ is well defined for most pipe junctions and fittings, the literature has limited documentations of $K$ for crosses. This study was commissioned to determine $K$ for a wide range of flow combinations in a pipe cross with equal diameter pipes and varied flow combinations. This study provides and innovatively presents over 1,000 experimental values of $K$ for designing and analyzing equal diameter pipe crosses.

This note compares the performance of various sediment transport formulas for a semiarid region of southern Italy (Puglia region). The sediment transport that occurs in the main streams of the region has been monitored for about 30 years (1958–1986) and the measured data are available at monthly intervals. The field data were compared with those predicted from four formulas (Ackers-White, Engelund-Hansen, Yang, and Van Rijn) selected on the basis of the sediment transport mode, the theoretical aspects, and the sensitivity to basic physical properties. The study examines the ability of the formulas to adapt to local conditions, the influence of time scale on predictions, and the accuracy of the prediction varying the discharge. The Engelund-Hansen and Van Rijn formulas (suspended sediment transport) estimate well the sediment load and are largely unaffected by variations in time scale. For low sediment loads, these formulas were less reliable.

The geometry of highway pavement and drainage inlets, especially cross slope, longitudinal slope, and local depression and transition length, usually determine the highway surface drainage capacity. In this study, a three-dimensional computational fluid dynamics (CFD) software, FLOW-3D, is used to develop models simulating unsteady, free-surface, shallow flow through curb-opening inlets, thereby demonstrating that an advanced CFD model can be used as a virtual laboratory to evaluate performance (i.e., inlet efficiency) of curb-opening inlets with different geometry conditions. Predicted intercepted flow and inlet efficiency agree well with laboratory measurements. Flow simulations were extended to smaller cross slopes for which laboratory tests were not conducted but which can occur in a highway transition.

Suspended-sediment concentration (SSC) in surface-water bodies such as rivers and reservoirs is one of the most important hydrologic data in solving engineering problems ranging from hydraulic design, river restoration, to water quality improvement and water resources management. Presently, obtaining SSC information relies primarily on direct manual collection, which is evidently affected by site accessibility, climatic condition, and safety concerns, not to mention the cost for sampling and laboratory analysis as well as turn-around time. There is need for alternative SSC measurement techniques suitable for continuous and real-time SSC measurements during hydrologic events where data are difficult to collect and are generally lacking or inadequate at present. This study examines the densimetric method to measure SSC, as a means of automated, continuous, and real-time collection in a laboratory setting with realistic sediments. Results showed good linear relations between SSC and the output current (milliampere) from the densimeter, and higher $R^2$ values are obtained from samples of finer particle sizes. The densimetric method performs better for smaller sediment sizes, especially when the sample SSC is high. Preliminary field results show promise in automated real-time SSC observations, demonstrating reasonable agreement with limited direct SSC sample results.