Journal of Hydraulic Engineering

Cavitation damage on a spillway is a very complex process. Although much research about cavitation and the resulting damage has been conducted for more than 30 years, existing methods for predicting cavitation damage on spillways are incomplete. This inadequacy results from cavitation damage limits (none to major) that are not exact points and from the magnitude and interaction of many factors that influence the damage. Using fuzzy mathematics, a model has been developed to predict cavitation damage on a spillway. Four factors that contribute to the damage are considered: cavitation index; flow velocity; material strength; and operating time. Fuzzy mathematics is used to set up five different damage levels from none to major and a comprehensive prediction model. The model had been tested with data from the left and right tunnel spillways at Glen Canyon Dam. The tunnels were subjected to serious cavitation damage in 1983. Using the operating data from both spillways, the model predicted damage levels, locations, and times close to the observed damages.

An important obstacle to the development of a generalized sump design is the variability of flow conditions in approach areas. The geometry and alignment of the areas immediately upstream of the sumps are so closely tied to the requirements of the specific site that it is virtually impossible to standardize their design. Flow conditions in approach areas, therefore, have to be evaluated on a case by case basis to determine their impact on the hydraulic performance of the respective pump sumps. This paper presents a case study of one particular sump design, developed through hydraulic model testing, which was highly dependent on approach flow conditions. The case study illustrates the effect on hydraulic performance and sump configuration of several design features and site constraints prevalent in approach areas. The study concludes that significant deviations from current design practices will be required to attain a generalized sump design.

This paper reports on measurements of radial jets using a laser-doppler anemometer and compares the mixing efficiency of a single radial jet with that of a single round jet under buoyant conditions based on experimental data. Dimensional analysis yields two parameters for the calculation of initial dilutions of jets and buoyant plumes. It is noticed that initial dilution of radial jets is much higher than that of round jets having the same source discharge, source buoyancy flux, outlet velocity and area because of intensive entrainment of the radial jet in the zone near the discharge point. Theoretical analysis indicates that the central velocity of the radial jet decays with jet path at a rate of −n ( n > 1), the value of which is proportional to the relative turbulence intensity and hence is related to the geometry of the radial jet. Experimental results show that in most situations, the value of n is approximately 1.5. Measurements also show that the ratio of half-width to distance from the virtual origin of the radial jet is given by b _w /r₀= 0.101 which is close to that of round jets. However velocity profiles of the radial jet are not completely similar, although the entrainment coefficient is basically a constant of 0.102. These results can help to predict correctly the flow field of the radial jet and its initial dilution.

The problem of irrigation canal regulation under demand delivery operation was formulated as an optimal control problem. To apply the linear optimal control theory, the Saint-Venant equations of open-channel flow were linearized using the Taylor series after using a finite-difference approximation on the original nonlinear, partial differential equations. A proportional-plus-integral (PI) controller was developed using the concepts of linear optimal control theory. Since the order of the controller gain matrix was large, an optimal observer (Kalman filter) was designed to estimate values for the variables that were not measured. An example irrigation canal with five pools was considered. With the finite-difference technique used, there was a total of 45 state variables and five control variables (gates) in the problem. With two measurements per pool, values for 35 state variables were estimated using the observer. By subjecting the canal to random disturbances of up to 40% of the initial inflow rate into the canal, the simulated performance of the global feedback control algorithm along with the Kalman filter was found to be acceptable in terms of achieving either a constant-volume control or a constant-level control in the canal pools in the presence of random disturbances in lateral flow rates.

A two-dimensional, vertically averaged, unsteady circulation model, using a nonorthogonal boundary-fitted technique, was developed in spherical coordinates for predicting sea level and currents in estuarine and shelf waters. Both the dependent and independent variables are transformed into a curvilinear coordinate system. The governing equations are solved by a semiimplicit method in which the elevations are solved implicitly and the vertically averaged velocities are solved explicitly. The model employs a space-staggered grid system and a three-level time discretization. Truncation errors are second order both in space and time. The model was tested against analytic solutions for a standing wave in a closed basin, tidal circulation in a simple rectangular channel with an irregular grid system and various degrees of rotation, and tidal flow in an annular section channel with quadratic bottom topography. The model was also tested against steady-state wind-induced setup in a closed irregular basin with constant depth represented by an irregular grid system. Comparison of the model predictions with the corresponding analytical solutions were very good. The model was applied to simulate tidal circulation in the Providence River. The agreement with available observations is very good. The model predicts that the tide exhibits a cooscillating wave pattern with tidal currents leading tidal elevation by 2.8 to 3.8 h depending on location for the M₂ tidal constituent. The M₄ and M₆ tidal components are significantly amplified because their frequency is close to the resonant frequency of the bay.

Rainwater infiltration through soils at landfills and other waste sites containing adsorbed chemical contaminants results in the continuous release of leachates into the ground-water environment. Due to continuous desorption of contaminants, the soils are progressively cleansed, and the contaminant concentration of the leachate diminishes with time. This paper presents a simple approach to estimate leachate concentration, residual contaminant levels of soils, and quantities of contaminants released into the ground-water environment after specified years of infiltration. Two desorption processes are analyzed: one using a constant distribution coefficient, and the other following Langmuir's equilibrium adsorption isotherm. This approach can be used to assess preand postremediation impacts of leachates originating at a waste site on ground-water environment in the vicinity.

This technical note presents the results of a laboratory study of the transition region from the end of a hydraulic jump to fully developed open channel flow. The velocity profile changes from that of a wall jet to the semilogarithmic form of open channel flow. In this region, the bed shear stress continues to decrease rapidly to eventually become constant. The intensity of flow on the centerplane decreases continuously to attain the relevant open channel value. The length of this transition region was found to be approximately equal to 10 times the tailwater depth for the range of Froude numbers studied, which varied from 3.87 to 10.48.

This study investigates local scour caused by a deeply submerged circular jet. Both a wall jet and an offset jet were used in the experiments with uniform cohesionless sediments making up the bed. Experiments conducted in both air and water show that the densimetric Froude number, F_o , is the main characteristic scouring parameter in the correlation of the maximum equilibrium scour dimensions. For an offset jet, the offset distance y , which is the vertical distance between the undisturbed bed level and the center of the jet, also affects the scour hole dimensions. A higher y causes the formation of a smaller scour hole because most of the energy is diffused into the flow instead of being used to erode the sediment. For the same F_o value, the size of the scour hole is consistently smaller for tests conducted in water than in air. The reason is attributed to the formation of a sediment ridge at the downstream end of the scour hole. Due to the density difference between air and water, the ridge height is markedly different in the two flow media.