Journal of Hydraulic Engineering

Size distributions of suspended sediment particles under low flow conditions in the Fraser River were measured using a submersible laser instrument. By comparing the in situ size distribution measured using this instrument with the size distribution of primary particles (measured by collecting sediment samples and analyzing them for size distribution after dispersing the particles by ultrasonic vibration), it was concluded that suspended sediment particles in the Fraser River downstream of pulp mill effluent outfalls are transported as agglomerations of particles (flocs) rather than as individual particles. Flocculation of river sediments in estuaries has been investigated in earlier studies, which show that saltwater intrusion contributes to the flocculation mechanism. Freshwater flocculation, such as the one observed in the present study, also has been reported in the literature, and it is attributed to the presence of organic materials and other contaminants from industrial and sewage treatment plant effluents. This paper describes the details of the submersible laser instrument and its use in the Fraser River, British Columbia, Canada.

The potential for enhanced removal of sediment from flowing water in a channel by means of settling on vegetation was studied theoretically and experimentally. Settling on vegetation was modeled as a distributed sink of sediment with vegetation spread throughout depth and length of the channel. Sediment-capture experiments were performed in a laboratory channel using model vegetation and well-sorted silt. The theory predicts that settling on vegetation has the potential to increase sediment-capture efficiency considerably, and this was demonstrated in the experiments. The enhancement of sediment removal was greater for artificial vines than for inclined strips. For the runs with flow velocities >10 mm/s the sedimentation efficiency was less than predicted. The reduced efficiency could be related to bed destabilization (which was observed in some runs), re-entrainment from the vegetation, or sediment sliding off the vegetation.

This paper presents the basic equations for a mathematical model of sediment-laden flow in a nonorthogonal curvilinear coordinate system. The equations were derived using a tensor analysis of two-phase flow and incorporate a natural variable-density turbulence model with nonequilibrium sediment transport. Correspondingly, a free-surface and the bottom sediment concentration are employed to provide the boundary conditions at the river surface and the riverbed. The finite analytic method is used to solve the equations of mass and momentum conservation and also the transport equation for suspended sediment. To demonstrate the method, the sediment deposition for the Three Gorges Project is considered. The mathematical model specifies the boundary conditions for the inlet and outlet using data from physical model experiments. The results for the mathematical model were tested against laboratory measurements from the physical model experiment. Good agreement and accuracy were obtained.

A series of laboratory test results are presented concerning the boundary shear stress, shear force, and discharge characteristics of compound meandering river sections composed of a rectangular main channel and one or two floodplains disposed off to its sides. Five dimensionless parameters are used to form equations representing the total shear force percentage carried by floodplains. A set of smooth and rough sections is studied with an aspect ratio varying from 2 to 5. Apparent shear forces on the assumed vertical, diagonal, and horizontal interface plains are found to be different from zero at low depths of flow and change sign with an increase in depth over the floodplain. A variable-inclined interface is proposed for which apparent shear force is calculated as zero. Equations are presented giving proportion of discharge carried by the main channel and floodplain. The equations agree well with experimental and river discharge data. Using the variable-inclined interface, the error between the measured and calculated discharges for the meandering compound sections is found to be the minimum when compared with that using other interfaces.

This paper investigates the generation of flow mass errors in finite-element shallow water models and the effect of these errors in the mass conservation of Eulerian-Lagrangian transport simulations. Flow mass errors are shown to be similar for several primitive and wave equation formulations. These errors occur primarily in areas of steep bathymetric gradients and near complex boundaries. Forcing Eulerian-Lagrangian transport simulations with nonconservative flow fields generates important mass imbalances, which can be mitigated by refining the flow grid. Comparatively, refining the transport grid only reduces marginally the mass errors.

The hopscotch finite-difference technique is shown to be a fast and accurate way to simulate transient, saturated, ground-water flow in relatively typical but heterogeneous 2D and 3D domains. The odd-even hopscotch (OEH) and line hopscotch methods are reviewed, and their implementation for saturated ground-water flow is presented. The OEH scheme, which is a second-order accurate explicit process, is efficient, requiring only six floating point operations per mesh node and time step, and is unconditionally stable (for saturated ground-water flow). Numerical experiments on typical 2D meshes (2,500 nodes) with synthetic, randomly heterogeneous hydraulic conductivity, suggest that the OEH process is approximately 1.5 times faster than the alternating direction implicit method and 3–4 times faster than the Crank-Nicolson implicit method using preconditioned conjugate gradient iteration. Similar experiments on medium-sized 3D meshes (87,500 nodes) suggest that the OEH process is between 7 and 10 times faster than the Crank-Nicolson preconditioned conjugate gradient method. Although the numerical results presented illustrate only typical test problem performance, they nevertheless clearly indicate promise for using OEH to simulate transient ground-water flow in 2D and, especially, 3D heterogeneous domains requiring fine spatial meshes.

This paper describes a large-scale physical model study concerning the minimum submergence required for double-entrance pressure intakes, such as used for power tunnel intakes. Use of minimum submergence can avert the occurrence of subatmospheric pressure and air-entraining vortices, and avoid reducing the efficiency of the turbine and its vibration of the turbine, etc. The scale of the double-entrance intake model, 1:30, which is primarily designed for the Three Gorges project, is almost the largest in the world. Based on analysis of the experimental data, an empirical formula is obtained and then it is compared with Gordon's formula, which is used mainly to calculate the minimum submergence before single-entrance intakes. The empirical formula is useful in the design of double-entrance pressure intakes.