Journal of Hydraulic Engineering

The development of armor layers in nonuniform sediments was investigated experimentally. Study objectives included extending the available data for high shear stresses and defining a criterion for the critical armoring condition. A new experimental technique incorporating an adjustable sediment support table, which provided uniform flow and constant shear stress throughout an experiment, was used. A nonuniform sediment forms stable armor layers for a range of shear stresses, bounded by an upper limit beyond which all grains are indiscriminately in motion and armor layers cannot form. The limiting stable armor layer formed at the highest shear stress is called the critical armor layer and the shear stress the critical shear stress. The dimensionless critical shear stress depends on the ratio of the maximum and median particle sizes of the sediment, decreasing as the ratio increases. The median particle size of the critical armor layer is the maximum particle size divided by 1.8, equivalent to a geometric standard deviation of 1.5. Thus, the composition of the critical armor layer corresponds to a lower limit of a nonuniform material. Uniform sediments do not armor.

The Glen Canyon Dam, located in the northeastern corner of Arizona, is operated to satisfy peak power demands of neighboring states. The discharge regime of the dam is such that the river stage in the Colorado River downstream of the dam varies diurnally as much as 4 m in some sections. It is alleged that these fluctuations of the river stage are responsible for the destruction of sandbars and, as a result, the loss of the extant biomass and the reduction of recreational facilities. In this paper, an analysis is developed to determine the equilibrium slope below which slope failures (mass wasting, bank failures) due to seepage of bank‐stored water would be unlikely. The sediments enclosed by the equilibrium seepage slope (range 11°–14° for the sediments downstream of the Glen Canyon Dam) and the maximum slope angle (range from 26° to 32°) is subjected to ongoing aggradation and erosion. Field data from ground surveys support the analysis described in this paper.

Modern monitoring devices can inexpensively extract a huge amount of data from water‐distribution systems through measurements of pressure (and sometimes flows). These data can be used in algorithms for transient analysis, time‐lagged calculations, inverse calculations, and event detection to continuously determine the calibration and the general state of health of the distribution system. The last three calculations depend on the first. The most useful of those three is the inverse calculation, which can calibrate while determining leaks or unauthorized use. A key to efficient calculation is the adjoint solution of the system (generally easier than the transient analysis) to find gradient data and a Jacobian matrix. These are used to find a Hessian matrix, which is used in the Levenberg‐Marquardt method to adjust parameters so as to minimize the difference between calculated and measured heads. The adjoint method is also used to compute sensitivities, which are valuable in judging the quality of the solution.

Clear‐water scour around a bridge abutment in the floodplain of a compound channel was investigated. Experiments were conducted in a flume with a fixed‐bed main channel and a movable‐bed floodplain in which the abutment terminated. Flow depth, discharge, compound‐channel geometry, and abutment length were varied, and measurements of approach velocity distribution and scour depth were obtained. A preliminary relationship for the dimensionless scour depth is suggested to illustrate the compound‐channel effects on scour. The proposed relationship is limited to the range of values covered by the variables in this study.

The phenomena of local scour and sediment transport due to a horizontal jet issuing from a sluice and flowing over a rigid apron, then on to an erodible bed, have been investigated. Based on experimental data, the scour characteristics have been correlated through the development of empirical expressions for the time to reach equilibrium stage, the locations of maximum scour depth and peak of dune, and the variation of maximum scour depth with time. Similarity criteria for the predication of development of the scour hole and sediment transport have also been developed and, apart from the flow parameters and sediment properties, the jet diffusion characteristics play an important role in these processes. The empirical relationships developed in this study highlight the necessity of an individual assessment when developing the similarity criteria for a particular flow situation.