Journal of Hydraulic Engineering

An analytical model for calculating the lateral distribution of the depthaveraged primary flow velocity in meandering rivers is presented. A small perturbation approach is used to linearize the governing equations. The well‐known “moment method,” commonly used to solve the concentration distributions, is then used to obtain an approximate solution. This makes it possible to take into account the convective transport of primary flow momentum by the secondary flow. This oft‐neglected influence of the secondary flow is shown to be an important cause of the redistribution of the primary flow velocity. The model, when tested with laboratory data, gives substantially better results than several previous models.

Part I of a two‐part report presents model and prototype research studies which have been conducted in the United States and Great Britain to evaluate how embankments for dams, levees, roadways, etc. perform when subjected to overtopping flows from probable maximum flood (PMF) or near‐PMF events. With improvements in the collection of flood records and the development of estimated storm events a significant increase in predicted PMF has been realized in some areas of the United States and other countries. These studies provide the engineer with an understanding of the mechanics of overflow erosion through subjecting scale model and prototype embankments to overtopping flow events. The effectiveness of various protection systems in preventing overflow erosion is evaluated. These systems range from grass‐lined embankments and spillways to more sophisticated protection using geotextiles, gabions, riprap, cellular concrete blocks and soil cement. Such research efforts provide for the development of cost‐effective measures that allow embankments to pass these extreme flood events without breaching.

This is a companion report to “Mechanics of Overflow Erosion on Embankments. I: Research Activities.” It discusses the hydraulics of water flowing over an embankment which is considered to be the basis for understanding the erosion process during overtopping events. The behavior of embankments that are subjected to overflow flood events are reviewed. Further information is developed based on results of research and actual case histories of embankment dams, levees, and roadways that have experienced overtopping. This report also provides information on the various protection systems that have been developed to prevent erosion of dam, roadway and levee embankments during overflow, including those tested in Part I. Case histories of several cost effective modifications made to embankment dams to permit overtopping are also discussed. The knowledge gained from using these hydraulic and design considerations provides the engineer and dam owner further information in the development of cost effective measures that allow embankments to pass extreme flood events without breaching.

Physical processes constituting fine, cohesive sediment transport in estuarial waters are described. These processes, which include settling and deposition, consolidation, erosion and transport in suspension, are typically interlinked by the cyclic nature of the tide dominated environment. Complexities in process characterization arise as a consequence of the dual dependence of sediment aggregate properties on the physico‐chemical properties of the sediment‐water mixture as well as the turbulent flow field. Present day knowledge of the processes enables reliable predictions of rates of sedimentation and erosion in navigable channels, waterways and harbors through numerical modeling. Further research is required for improving procedures for measuring settling velocities, identification of depth at which a definable bed is encountered, and the behavior of near‐bed high density suspensions.

Typical engineering applications involving cohesive sediments in tidal water bodies including bays, estuarial navigation channels, small harbor basins, piers, and wharves have been cited. Reference has been made to problems in reservoirs and in the muddy coast environment. Techniques for prediction of estuarial sedimentation include field methods, physical and numerical modeling, and hybrid modeling which optimally combines physical and numerical modeling approaches. In many cases simple, zero‐dimensional modeling yields results of acceptable accuracy. Three‐dimensional numerical models have recently been developed for analyzing situations in which the complex structure of flows and associated sediment motion cannot be simplified. Further progress in improving the accuracy of prediction of sedimentation rates can be made by better understanding the basic laws governing cohesive sediment behavior, and by developing new strategies and instrumentation for data collection.

This paper presents a review of theoretical and conventional experimental approaches to studies of wind‐induced water currents and introduces a new method for simulating these motions in the laboratory. Mean velocity profiles obtained in conventional air‐water systems when plotted in terms of the coordinates of the “smooth inner” law of velocity distribution, relegate all of the experiments into the region of transitional roughness. The shortcomings of laboratory air‐water systems such as uncontrollable surface roughness and three‐dimensionality of flow are overcome with novel experimental approach in which the actual water body is represented by the air volume contained inside a moving box, and the surface of a stationary wall constitutes the actual air‐water interface. Mean velocity profiles obtained with this apparatus are used to verify an analytical solution based on the parabolic distribution of the eddy viscosity.

DEMOS is an interactive model for the analysis and design of dendritic sewer networks. It routes hydrographs and pollutographs through conduits and detention basins on the basis of the one‐dimensional advection‐diffusion equation. The equations are solved numerically by exploiting the numerical diffusion inherent in the finite difference approximation to a simple advection equation. The model parameters may then be related to the hydromorphologic characteristics of the system. Steady or looped rating curves may be used to convert between flows and depths. The conduit geometry may be circular or trapezoidal. The model accomplishes pipe design by selecting pipe sizes that ensure open channel flow at all times, while accounting for transient, nonuniform flow conditions and storage in the conduit. For flow simulation, surcharging is identified, and a simple flow volume storage procedure is undertaken. The model includes several features that allow for easy implementation on a variety of systems, including microcomputers. Use of the microcomputer version of DEMOS, a public domain FORTRAN code, is demonstrated in an example that involves the simulation and design of a branched sewer network.