Journal of Hydraulic Engineering

This paper presents the development and application of a three-dimensional oil spill model for predicting the movement and fate of an oil slick in the coastal waters of Singapore. In the model, the oil slick is divided into a number of small elements or grids for simulating of the oil processes of spreading, advection, turbulent diffusion, evaporation, dissolution, vertical dispersion, shoreline deposition and adsorption by sediment. This model is capable of predicting the horizontal movement of surface oil slick, the mass balance of oil spill and the oil particle concentration distribution in water body. Satellite images and field observations of oil slicks on the surface in the Singapore Straits, and measurements of the vertical concentration of oil particles in flume are used to validate the newly developed model. Compared with the observations, the numerical results of the oil spill model show good conformity.

An objective methodology is proposed for evaluating the hydraulic performance for possible rehabilitation of sewer systems. It involves assigning a hydraulic performance index to each pipe section. This hydraulic index reflects both the local surcharge in a pipe and the surcharge induced at upstream sections of the same branch in a sewer network. The hydraulic index also takes into account the vulnerability and the retention capacity of each pipe section. This index may be used directly to establish the rehabilitation priority of different sections to maximize hydraulic performance for the entire network. This methodology was successfully applied to the sewer system of the city of Laval in Canada. The results show how pipe dimensions and locations have the effect of surcharging or relieving a pipe network and how the hydraulic performance index adequately rates the contributions of sewer network components.

One of the main mechanisms of failure of levees is a phenomenon called “piping,” which generally begins with the formation of a sand boil at the leeward side of the levee, and has been frequently observed to proceed upstream along the base of the levee through a slit formation. The issue of most important concern is to estimate the critical head that could promote the occurrence of piping. Considering the flow through porous media and coupling it with Bernoulli’s equation and a critical tractive stress condition, a model is developed for the critical head. Using appropriate transformations, the proposed model takes on a form which supports Bligh’s empirical findings. Another model based on critical velocity is also developed to estimate the critical head. The functional form of these two models is evaluated using the critical head versus porosity data from a number of laboratory studies conducted in the Netherlands. These models were found to perform better than did Terzaghi’s model.

In this work the complete equations of one-dimensional unsteady flow in open channels in integral form, and compatibility equations at the junctions of a channel network, are solved numerically. Analytical integration in space is used between each pair of consecutive irregular sections of a channel, and the nonprismatic term is expressed in terms of uncoupled functions of the geometry at the sections. The linearized system of equations for each time interval is solved by an elimination method based on a double-sweep algorithm. The model is applied to the estuary of the San Juan River in Venezuela, where oscillating currents by effect of semidiurnal tides take place and the amplitude of the wave at the mouth is amplified toward the inland direction. Alternating drying and filling is simulated by means of slight modifications in the bed geometry of upper river sections. Measured water elevation and flow rates available at two stations are used to calibrate the model, and a very accurate adjustment of the tidal levels observed in the river is obtained.

The movement of water from a shallow aquifer to a semiconfined aquifer through a localized area of leakage in an aquitard, designated as an aquitard window, is an area of concern in certain gulf coastal plain aquifer settings. Locating these windows, or areas of leakage, has been historically arduous. The purpose of this study was to evaluate the use of a genetic algorithm (GA) technique as an inverse technique for locating highly probable areas of leakage based upon aquifer head data near the suspected area of leakage. The GA technique has previously been tested on synthetic data alone, and this research offers insight into the capabilities of the technique with actual field data from a site with a known aquitard window. Research sites with historical and ongoing data collection efforts are rare and offer the best opportunity for robust evaluation of new methodologies. Based upon the GA technique, the steady-state accretion flux to the Memphis aquifer at the Shelby Farms study site was determined to be 12,346 m³/day with a standard deviation of 821 m³/day and compared well with the range from 510 to 9,911 m³/day previously determined for the site.

Experimental results indicate that an additional lateral deflector built on the outlet can increase the cavity length in aerators with a sudden vertical drop and lateral enlargement. Observation shows that the cavity length is affected by both the vertical and lateral dimensions of the deflector. A larger deflector increases the cavity length substantially and connects the bottom cavity with the sidewall ones which results in more sufficient aeration. However, the backward flow on the bottom may reduce the length of bottom cavity and the effectiveness of aeration. Factors affecting the bottom cavity length, including the slope of the outlet, the bucket angle of sill, and the shape of lateral deflector, should be included in the estimation of the bottom cavity length. Based on test results, an equation has been proposed to predict the cavity length.

Previously, it was shown that, in Turner’s formula which predicts the penetration depth of negatively buoyant jets, the classical initial densimetric Froude number should be replaced by an initial effective Froude number if the formula is applied to a heated water jet discharged downward. In the present paper, this conclusion is extended to double-diffusive plumes with two buoyancy components (heat and salt) which both oppose the downward flow. A new effective Froude number is introduced for double-diffusive plumes. For the calculation of the penetration depth a modified version of the integral Fan–Brooks model has been used. The same model is used to calculate the vertical penetration in the strongly nonlinear regions around the density maxima that appear in water at some special values of temperature and salinity. It is found that the penetration depth becomes very large if the existing ambient temperature and salinity are close to density extremum values and becomes infinite if the existing ambient temperature and salinity coincide with the maximum density values.

Based on probabilistic assessment of the consistency of piezometer water level increments and decrements, a piezometer membership function of a fuzzy set is introduced. By investigating the membership of the Tresna water reservoir piezometers in a fuzzy set, the watertightness of the seepage curtain was assessed, and, following the maximum degree of membership from headwater to tailwater, a seepage path through the left abutment of the Dobczyce dam was determined.