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Twenty-one roughly concurrent observations of hydraulic variables at the partially confined section A-2 and the wider section F for a reach of the Rio Grande near Bernalillo, N. Mex., form the basis for this study of flow resistance and sediment transport. In addition, the averages of the hydraulic properties of 13 cross sections for the reach are used to determine bar resistance and bedmaterial transport rates by the Einstein procedure. Some miscellaneous observations on standing waves and on flows with high sediment concentrations are given. Because bed configurations change, flow resistance for the Rio Grande varies widely. For lower regime flow, the bed configuration is dunes, and the flow resistance is high. Values of the dimensionless Chezy coefficient, C/Vff, range from about 9 to 12. For upper regime flow, the bed is relatively plane, the flow resistance is low, and Cfi/g varies approximately from 19 to 24. Flow in the transition region between lower and upper regime is characterized by variable bed configurations, flow resistance, velocity and depth, both laterally at a cross section and from section to section along the reach. Width adjustments are effected by channelization. Both width adjustments and minor variations in characteristics of the bed material reflect a tendency for the channel to maintain continuity of bed-material transport. Flow resistance is consistently greater at the narrow section A-2 than at section F. The Einstein bar-resistance curve does not adequately describe the flow resistance for either of these cross sections. However, data for the average of 13 cross sections in the reach fit the bar-resistance curve reasonably well. High concentrations of suspended sediment have more effect on the values of overall resistance coefficients for lower regime flow and flow in the transition region than for upper regime flow. Transport rates of bed material are estimated by several methods and compared with the transport rates of measured suspended sand. High concentrations of bed material accompany high velocity and low flow resistance. The interrelation of sediment transport and flow resistance is complicated by the extreme variability of water and sediment discharge and by the time-dependency of sediment concentration during flood events. INTRODUCTION Studies of flow phenomena in alluvial channels have been conducted mostly in carefully controlled laboratory experiments. It is sometimes difficult to extend the results of such studies to natural channels HI H2 STUDIES OF FLOW IN ALLUVIAL CHANNELS because field data often are inadequate or incomplete. Comparable field studies are difficult to conduct, and the interpretation of field data is complicated by the indeterminacy introduced from nonuniform flow conditions and from the inherent inaccuracies in measuring, estimating, or sampling some of the factors involved. Nonetheless, it is of interest to consider field data in the light of carefully controlled laboratory investigation and, with due consideration of the limitations of field measurements, to examine some of the observed similarities and differences in the experimental and natural conditions. PURPOSE AND SCOPE This paper presents the results of a series of observations of ike Rio Grande near Bernalillo, N. Mex. The characteristics of flow resistance are described qualitatively in terms of flow regime and bed configuratiqn, and quantitatively in terms of standard resistance coefficients and of the Einstein bar-resistance curve (Einstein and Barbarossa, 1952). Some limited data for flows with high concentration of suspended fine material are given. The magnitude of the resistance coefficients, the regimes of flow, and the general forms of the bed configurations are compared to those reported in several flume investigations. Sediment transport rates are computed by the modified Einstein method (Colby and Hubbell, 1961) and by the method proposed by E. M. Laursen (1958). For several observations, transport rates are estimated using the Einstein bed-load function (Einstein, 1950).

Aspects of flow resistance and sediment transport, Rio Grande near Bernalillo, New Mexico