Journal of Hydraulic Engineering

Most gravel rivers show a tendency for characteristic grain size to decrease in the downstream direction over scales of tens or hundreds of kilometers. It has been surmised that this downstream fining is due to some combination of selective sorting, by which finer grains are preferentially transported downstream; and abrasion, by which individual particles are reduced in size. Here a framework for the simultaneous treatment of both phenomena is developed. The analysis is restricted to bed‐load transport of gravel. Only abrasion due to binary collisions between moving bed load and stationary bed particles is considered. The formulation includes the possibility of differential basin uplift and subsidence due to tectonism, and mixtures of rock types with differing coefficients of abrasion. The formulation of selective sorting is based on the concept of hiding, as applied to a surface‐based bed‐load transport relation. Abrasion is first treated in terms of a Lagrangian formulation for individual grains, and then transformed into an Eulerian expression that appears in the formulation of gravel mass balance.

Most gravel rivers show a tendency for characteristic grain size to decrease in the downstream direction over scales of tens or hundreds of kilometers. It has been surmised that this downstream fining is due to some combination of selective sorting, by which finer grains are preferentially transported downstream; and abrasion, by which individual particles are reduced in size. Here the framework for the simultaneous treatment of both phenomena, developed in a companion paper, is used to analyze several cases of interest. In particular, wavelike aggradational profiles of permanent form are considered. An application to the Red Deer River, in Alberta, Canada, as well as several hypothetical cases, suggests the following result. In the case of quartzite, selective sorting controls downstream fining; in the case of limestone, abrasion and selective sorting are of roughly equal importance; and in the case of a mixture of quartz and limestone, abrasion ceases to be important beyond some characteristic length scale required to grind the gravel‐sized limestone out of existence.

The vortex‐settling basin (VSB) is a fluidic device that uses only the vortices of the flow to remove sediment. This is an economical, efficient, and water‐conserving alternative to the other available sediment‐extraction devices. This paper presents guidelines for designing and modeling VSBs. It shows that the circular basin should have diameter equal to five times (as compared with six times stipulated in American practice) the bed width of inlet canal. The distinctive features of the proposed design are formation of free vortex in the outer region and flow in the basin traversing a relatively longer path before reaching the overflow weir. Extraction of sediment smaller than 0.5 mm is optimized when a diaphragm and a deflector are incorporated in the inlet canal and basin, respectively. Diameter of the flushing pipe and the flushing discharge to be adopted for the extraction of different sediment fractions are specified. Formulas suggested for prediction of trapping efficiency are simpler and more reliable than several existing formulas. Experiments indicate 76% utilization of the VSB volume and, therefore, show a better performance compared to standard sediment tanks.

A fairly simple correlation is formulated for calculating the suspended sediment‐transport capacity of open channel flow. The correlation is based on the assumption that the work performed by buoyancy force on the sediment particles is proportional to the production of turbulent kinetic energy. The proportionality constant is determined by calibration using a wide range of experimental data. The new formula does involve bed‐load correlations, and, hence, avoids the considerable uncertainty generic to those correlations. By assuming a suitable concentration profile, the formula can be used for calculating the maximum, full‐capacity concentration at a reference level, but the formula itself does not involve a priori profile assumptions. An approximate relation is provided between the depth‐averaged concentration and the transport concentration itself. This makes it possible to calculate easily the reference bed concentration using a graphical chart provided for the cases where the Rouse profile for concentration is a good approximation.

Submergence of hydraulic jumps occurs frequently at low overflow structures, such as weirs and low‐head dams. In these cases the jump degenerates into a rotating current that produces a strong upstream‐directed surface velocity in an otherwise seemingly quiescent downstream pool. This vortex is commonly called the hydraulic by canoeists and water safety experts who fear and respect its potential to maim and kill, yet the phenomenon is virtually unknown in the hydraulic engineering literature. Using analysis and experimental evidence, the paper shows how the hydraulic may be eliminated by either increasing the height of the structure sufficiently to promote formation of a proper hydraulic jump, or by adopting the cascade concept of continuous energy dissipation on a baffled chute. In the former instance, the required height can easily become so great, however, that it may be deemed unacceptable. On the other hand, baffled‐chute spillways are environmentally attractive, known to function well over a wide range of operating conditions, and completely independent of tailwater depth.

Safety inspection of dams can be scheduled on a probabilistic basis considering detectability and repair probability. In this paper, a method of inspection scheduling for a dam is suggested by using an availability model. Unavailability is defined as the state in which a dam is operating under unsatisfactory conditions with deficiencies. The deficiencies may or may not be detected in an inspection, and a detected deficiency may or may not be repaired in due time. The paper proposes to relate the expected availability of a dam to the frequency of dam inspection, the detectability of the inspection routine, the likelihood of owners' compliance to repair orders, and the construction quality of the given dam. The deteriorating characteristics of a dam with time could also affect its availability. The case of inspection scheduling for a nonaging dam is first developed, followed by the case of an aging dam. Examples are given to demonstrate the proposed procedure.

In this paper, an approximate algorithm is proposed to eliminate false negative (gauge) pressures that appear during the analysis of a water‐distribution system. Emphasis is placed on the solution of the problem rather than on its cause. The formulation is based on a system of equations for a network that has been constructed using the continuity equations for each node and the head‐loss equations for each pipe. It contemplates two situations: one in which the elimination of a false negative pressure leads to the emptying of all the pipes that join a node, and the other in which the conditions are such that the elimination of the negative pressure leads to one or more pipes flowing partially full as an open channel. Two examples are presented to illustrate the applicability of the approximation, one for an imaginary simple network and the other for a water‐delivery system in a large city.

The effects of uncertainty in Manning's roughness coefficient and the empirical nature of Manning's equation on return period of flood stages have been analyzed using first-order reliability methods (FORM). This method generally used for structural reliability was applied to hydraulics by using Manning's equation as the basis for a limit state function. This paper also describes a way to compare the FORM results, a safety index, to the results of the traditional frequency method, a probability, by changing both to a return period.

In the computation of advection-diffusive contaminant transport, the Holly-Preissmann characteristics scheme for the advection operator is known to be quite accurate and stable. However, these qualities are obtained at the expense of having to solve an auxiliary transport problem for the concentration derivative. This paper shows that the Holly-Preissmann Hermite cubic interpolating polynomial can be replaced by a cubic-spline interpolating polynomial, thus obviating the need to solve the auxiliary problem. Although the cubic-spline approach lacks some of the intuitively appealing features of the Holly-Preissmann approach, it is nearly as accurate while offering a computational time saving of 20%–30%, with a corresponding reduction in code size. The paper outlines the computational procedure, and presents demonstrative calculations illustrating the performance of the method for the familiar test case of advective transport of a Gaussian contaminant distribution.