Journal of Hydraulic Engineering

The hydraulic jump is a fascinating subject that has been the subject of several hundred technical papers. The study reported herein, sponsored by the National Science Foundation, provides information on extreme pressures in the hydraulic jump, an area that has not received sufficient coverage in earlier work. Data are presented for Froude numbers from 3–10, with both developed and undeveloped incident flow, test runs up to 24 hr in length, chute slopes of 0°, 15°, 30°, and 45°, jump locations on the chute as well as at the toe of the chute, and with and without chute blocks, intermediate blocks, and end sills. Peak values of RMS dimensionless pressure fluctuations Cp' up to 0.10 and dimensionless pressure fluctuation Cp‐values up to 1.3 were obtained. The peak value of Cp depended on location in the jump, chute slope, incident Froude number, incident flow development, and the length of test run. Brief data on areal coverage of pulses are also included. The normal distribution did not conform to extreme pressures.

Hydraulic structure failure such as the failure of the spillway of a dam may afford the opportunity to evaluate the impacts of this type of event on the formation and migration of a scour channel upstream of the spillway. Such an event occurred in November 1985 at the Lake Charleston dam in Illinois. A portion of the spillway failed during a moderate flood event, and the resulting concentrated flow developed a scour hole (“sinkhole”) which migrated upstream until its movement was halted by a rock ledge. The bed elevation of this scour channel was much lower than the original lake bed. Field data on velocity distribution, bed material characteristics, stream gradient, and stream cross sections were collected to evaluate this hydraulic phenomenon. These data and existing streamflow and sediment rating information were used to simulate the development of the scour channel. The HEC‐6 model was found to simulate this event quite satisfactorily. Analyses such as this can be a valuable tool in evaluating natural disasters such as the sudden failure of overflow structures along a waterway.

Field data gathered from 43 river reaches of Calabria (southern Italy) were employed to develop a theoretically based equation for predicting the f‐friction factor that takes into account both the Froude number and the sediment mobility parameter. The river reaches investigated have: (1) Reasonably uniform and relatively low flow; (2) no appreciable vegetation in the channel bed and banks; (3) a fully developed turbulent flow; (4) a friction slope greater than 0.2%; (5) small and intermediate scale roughness; (6) a mobility parameter greater than the critical value in more than 50% of the cases; and (7) a Froude number between 0.20–1.30. Statistical techniques were used to derive an equation for estimating f that takes into account the physical processes controlling flow resistance beyond the range of the collected data.

A rotational viscometer has been designed for laboratory measurements of the rheological properties of natural mudflow deposits in Colorado. The mudflow matrices comprised of silt and clay particles are sheared under temperature‐controlled conditions at volumetric sediment concentrations ranging from 0.10–0.45. This study stresses the importance of conducting rheological measurements at low rates of shear because: 1) Those are the conditions found in natural channels; and 2) they avoid the slippage problems observed at large sediment concentrations. At low rates of shear, the Bingham model is fitted to the measured rheograms, and both the viscosity and yield stress increase exponentially with the sediment concentration of the fluid matrix. Both the yield stress and the viscosity increase by three orders of magnitude as the volumetric concentration of sediments in the fluid matrix changes from 0.10 to 0.40. The addition of sand particles does not significantly alter the rheological properties of the matrix unless the volumetric concentration of sands exceeds 0.20.

Existing methods based on the diffusion theory have been extended to determine the sediment concentration distribution for large concentrations of sand. The modifications for volumetric concentrations ranging from 4 to 20% include decreased fall velocity, and increased viscosity and specific weight of the suspension. The sediment concentration profiles are sensitive to the velocity profiles and the fall velocity of sediment particles. In turbulent flows, either a power law or a two‐layered logarithmic law can be used to describe the velocity profiles and the sediment difiusivity. The proposed method accurately depicts the deviation from the Rouse equation at large concentrations of sands, and the agreement with sediment concentration profiles measured by Einstein and Chien is excellent. The proposed numerical solution gradually reduces to the relationships of Karim and Kennedy, and Rouse as the volumetric concentration decreases below four percent.

The log‐Pearson type 3 (LP3) distribution is recommended in the United States by the Water Resources Council (WRC) as the parent distribution to maximum annual flood series. The parameter estimation technique proposed for this distribution consists in applying a logarithmic transformation to the observed flood sample and then applying the method of moments to these logarithmic values using moments of order 1, 2, and 3 (mean, variance, and coefficient of skew) in log space. Other methods have been proposed which use only moments in real space such as the mean, variance, geometric mean, harmonic mean, etc. of the observed sample, or combination of moments in real and log space (method of “mixed moments”). There are many other versions of the method of moments which have yet to be explored and evaluated. To help motivate this kind of exploration, we derive a general formula for the variance of the T‐year event $X_T$ obtained by a method called the Generalized Method of Moments (GMM) which combines any three moments of the LP3 distribution. We also present a special case of the GMM which we call the Sundry Averages Method (SAM) which uses the harmonic, geometric, and arithmetic means of the distribution.

A common outfall configuration in practice involves a buoyant discharge through a horizontal circular pipe into a shallow body of water. A detailed experimental study of the near‐field flow and mixing characteristics is presented. The proximity of the bed and the free surface has a significant influence on the flow pattern. Experimental results are adequately represented by length and buoyancy scales defined by source momentum and source buoyancy flux. Jet path, centerline dilution and horizontal and vertical half widths are compared with an integral model in an unconfined environment.

Screening-type analyses of groundwater contamination are often performed without site-specific information on groundwater flow velocity, among other aquifer characteristics. This note defines a maximum point concentration velocity (MPCV) as a groundwater velocity value resulting in a theoretically maximum concentration of a radionuclude at a specified location. For one-dimensional plug flow, MPCV is the product of the distance from the source, the radioactive decay rate, and the sorption retardation coefficient (MPCV=xΙR_d). MPCV for two-dimensional advective-dispersive transport is a function of these parameters and additionally the longitudinal dispersivity. A closed-form approximation for this MPCV is presented which provides a better estimate than the plug-flow MPCV. Calculated concentrations are more sensitive to velocity for low velocity values, when decay is most important.

This note presents the results of an experimental study on the hydraulics of pool and weir fishways. A simple weir-type flow analysis is found adequate to describe the plunging flow regime. A surface stream analysis is performed to predict the characteristics of the streaming flow. A parameter is developed to predict the transition from plunging to streaming flow.

Most of the existing weir formulas lose their significance as the ratios of head to height or head to width become large. A full range equation valid for all values of head-to-height ratio has been developed for a sharp crested weir. Also for finite crested weirs a full range equation valid for all values to head-to-width ratio has been presented. This equation covers narrow crested, broad crested and long crested weirs. Providing a smooth transition between sharp crested and finite crested weir equations, a generalized rectangular weir equation has been evolved. This equation is applicable to all head-to-height ratios and all head-to-width ratios or sharp crested and finite crested weirs. This equation is applicable to all types of rectangular weirs-sharp crested or broad crested, and sills. It is hoped that the equation will be useful for analysis and design purposes.