Journal of Hydraulic Engineering

A mathematical model based on the hydrodynamic shallow water equations is developed for numerical simulation of slide generated waves in fjords. The equations are solved numerically by a finite difference technique. To examine the performance of the numerical model we have simulated the slide catastrophe in Tafjord, western Norway, 1934. The predicted runup heights are in good agreement with measured runup heights. The effects of wave amplification are estimated in runup zones with gentle beach slopes. The model results reveal wave energy trapping due to the fjord geometry. This causes standing wave oscillations in accordance with the observations.

A bank‐stability analysis is incorporated into an analytical procedure for modeling the hydraulic geometry of an alluvial gravel‐bed channel. The new analysis includes a procedure that calculates the mean bed and bank shear stress as well as assessing the bank stability. The bank‐stability criterion accounts for the increased stability of the channel banks due to consolidation of the bank sediment, cementing by fines, and binding of the sediment by root masses. The two key parameters in the bank‐stability analysis are the median grain diameter of the bank sediment $D_{50\mathrm{bank}}$, and the modified friction angle of the bank sediment φ′. A sensitivity analysis of the two parameters indicate that the bank stability can exert a large influence on the channel geometry. This is supported by testing the theory on published field data. The bank sediment size was assumed to equal the bed sediment size, and the variation of the friction angle φ′ was investigated. The estimated φ′ values are seen to increase systematically with the bank vegetation density. The results indicate that increased bank stability induced by the vegetation has a significant influence on channel geometry; the vegetated channels are narrower, deeper, and less steep. For well‐developed bank vegetation, the channel widths, depths, and slopes were found to be in the order of 0.6, 1.4, and 0.9 times their respective unvegetated channel dimension.

This paper focuses on the mixing processes that develop when a buoyant jet from a round outfall pipe enters a shallow moving body of water. Results from a detailed experimental study quantify the effects on jet mixing produced when a current is imposed on shallow receiving water. Findings show that the dilutions of buoyant jets entering these environments are significantly different from those discharging into unconfined (deep‐water) conditions. Mixing features discussed include the application of scaling relationships in collapsing integral parameter data and the role played by the Coanda effect in influencing the mixing of jets. Patterns of jet path, centerline dilution, total dilution, horizontal and vertical half widths, and a novel width parameter are described and compared with shallow stationary and current affected deep‐water results.

This paper brings together recent data from the large‐scale Flood Channel Facility, Wallingford, England, with other model studies to investigate the main parameters affecting conveyance in meandering compound river channels. Parameters investigated include sinuosity, boundary roughness, main channel aspect ratio, width of meander belt, and flow depth above bank‐full level as well as the cross‐sectional shape of the main channel. The effect of each parameter is quantified through a nondimensional discharge coefficient F^*. Possible scale effects in modeling such flows are also investigated.

Experiments on the incipient motion of gravel and sand mixtures of 0:100, 10:90, 25:75, 45:55, and 100:0 percent ratios of gravel and sand, respectively, were made in a laboratory flume. A series of transport experiments was made for each of the five sediment beds and the critical shear stress for motion was calculated for 12 size ranges by interpolating or extrapolating the bed shear stress for a very small transport rate. The sand in each of the five bed mixtures began to move at nearly the same bed shear stress. All gravel sizes began to move at nearly the same bed shear stress in the 100% gravel experiments, but in the sand‐gravel experiments the gravel showed an increase in critical shear stress with increasing size. Reasons for this change in the initiation of motion of the gravel from the 100% gravel to the sand‐gravel mixtures may result from the abundant sand‐sized sediment inhibiting the formation of a coarse bed surface layer in the sand‐gravel experiments.

Steps leading to the numerical study of the hydrodynamic behavior of a compound open channel are described. The method uses an algebraic stress model imbedded, together with an energy‐dissipation model, in a parabolic pressure‐correction algorithm. The steps include the distinction between a compound channel and a channel with small longitudinal step in bed level, the applicability of the algebraic stress model to flow along a 270°corner formed between the flood‐plain bed and the main‐channel bank, justification of the use of the flux boundary condition for the dissipation at the free surface of the compound channel, and other topics.

Water‐surface profiles in a channel that includes either a contraction in channel width, or a rise in channel bottom are analyzed using the specific‐energy concept. It is discovered that the water‐surface profiles in this channel for particular flow conditions are not unique; two stable solutions and one unstable solution are found. The flow conditions leading to nonunique solutions are delineated.