Journal of Hydraulic Engineering

Several issues regarding the sampling and analysis of bed material from gravel bed streams are addressed in this paper. The need to convert surface samples into volumetric equivalents, and methods to do so, are explained. It is found that most surface samples are unique and, thus, are not directly comparable. Particular attention is paid to areal sampling with clay and with wax. The areal‐to‐volumetric conversion of samples removed from different sediment structures is also considered. Criteria are proposed for determining the minimum dimensions of unbiased volumetric samples. These criteria can be used to determine the minimum area of an areal sample. The minimum depth of a volumetric sample is shown to be larger than the depth of most surface layers. Thus, a surface layer can not be sampled volumetrically. A technique is presented for sampling a wide size range of underwater surface particles. This technique has been tested in the field and found to provide good results.

The turbulence characteristics of sediment‐laden flows in open channels are investigated using two‐component laser‐Doppler velocimetry. Suspensions of well‐sorted sands with diameters ranging from 0.15 mm to 0.24 mm, flowing over nominally flat beds, both fixed and erodible, are studied in a tiltable, recirculating flume. Various conceptual models that have been proposed to explain the mean‐field profiles are examined for consistency with respect to their implications for higher‐order characteristics. No evidence is found to support either the traditional model, associated with a decrease in the von Kármán constant, or the more recently proposed models based on simple analogies to slightly stably stratified wall‐bounded flows. A model based on small‐scale fluid‐particle interaction is suggested as more promising.

A number of techniques have been developed to compute the velocity distribution and, hence, the momentum and energy coefficients along a nonuniform open‐channel flow. Analysis of velocity distribution in the probability domain has made it possible to determine the cross‐sectional mean velocity and the momentum and energy coefficients without having to deal with the geometrical shape of cross sections, which tend to be extremely complex in natural channels. In the probability space, the area mean values can be obtained as the mathematical expectations that can be determined from the probability density function of velocity derived by entropy maximization. The capability of a velocity distribution, derived from the probability and entropy concepts, to describe various possible patterns of velocity distribution along a nonuniform flow has been demonstrated. Simple graphical methods to estimate a model parameter have also been developed for practical applications in study of transport processes in open channels, natural or man‐made, that are related to the velocity distribution.

In this paper, modifications of the method used to delineate flood‐plains on active alluvial fans for the national flood insurance program are suggested, given new data regarding the deviations of channels from the medial radial line at the apex of the fan. In the original methodology, it was assumed that every point on an alluvial fan contour had an equal probability of being impacted during a flood event; that is, a uniform probability distribution was assumed. Data now available suggest that a normal distribution better describes the probability of points on an alluvial fan contour being hit during a flood event. Results from an example of the application of the modified methodology are compared with the results obtained using the original methodology.

Extensions to the conventional method of characteristics allow transient conditions in simple pipe networks to be efficiently calculated. In particular, treating both boundary conditions and network topology in a general and comprehensive fashion simplifies the solution of many combinations of hydraulic devices. The algebraic framework presented includes a flexible integration of the friction loss term that reduces to previous linear approximations as special cases. In addition, an explicit algorithm is derived for a general hydraulic element called an external energy dissipator. This boundary condition conveniently represents surge tanks, relief valves, storage reservoirs, valves discharging to the atmosphere, and many other common devices. Significantly, the solution remains explicit even if friction losses and inertia effects are present in both the storage element and a connecting pipe. This comprehensive approach to transient analysis simplifies control logic, encourages accurate reporting of field data, and improves execution times. The procedure is illustrated by analyzing transient conditions in a small network containing a variety of devices.

Leak detection in water‐distribution systems can be accomplished by solving an inverse problem using measurements of pressure and/or flow. The problem is formulated with equivalent orifice areas of possible leaks as the unknowns. Minimization of the difference between measured and calculated heads produces a solution for the areas. The quality of the result depends on number and location of the measurements. A sensitivity matrix is key to deciding where to make measurements. Both location and magnitude of leaks are sensitive to the quantity and quality of pressure measurements and to how well the pipe friction parameters are known. The overdetermined problem (more measurements than suspected leaks) gives the best results, but some information can be derived from the underdetermined problem. The variance of leak areas, based on the quality of system characteristics and pressure data, indicates the likely accuracy of the results. The method will not substitute for more traditional leak surveys but can serve as a guide and supplement.

Curb-opening inlets have been used extensively in urban and highway drainage systems. Until quite recently, the numerical solution of equations for determining the water-surface profile and curb-opening inlet discharge was tedious. The result was that approximate methods were used based on experiments conducted over a limited range of the many variables involved. This study develops a new hydraulic design procedure for curb-opening inlets based on experimental data. The results are presented in graphical form for practical use. The experiments cover supercritical regimes and observed water surface profiles, for which the interception ratio of curb-opening inlets to main street discharge can be presented by dimensionless parameters related to length of curb-opening inlets, Froude number, and width of spread.

A theoretically based method for taking into account the effects of bank vegetation on channel-flow parameters is outlined. It can be used to predict what effect changes in bank vegetation will have on the discharge capacity of a channel and to make comparisons of bank-vegetation effects between channels. Using the analysis on individual channels may aid in gauging the true impact of bank vegetation on in-bank flow capacity and in deciding whether the beneficial effects of bank vegetation in stabilizing banks outweigh any adverse effects that result from the potential reduction in discharge capacity. Using this method, the effect bank vegetation has on channel discharge capacity is shown to decline rapidly as the width-to-depth ratio of channels increases. When seasonal growth of vegetation is simulated the effect on channel discharge capacity is shown to be less than 10% for channels with a width-to-depth ratio greater than 16.