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An algorithm is developed that relates depth to discharge and determines bed- and suspended-load transport for the entire range of bed forms found in sand-bed channels; equilibrium-state geometry of lower flow regime bedforms is also predicted. Grain shear stress and form resistance are differentiated using a drag coefficient closure and a two-segment logarithmic velocity profile. A Meyer-Peter-type formulation is used to compute sand transport in the bed-load layer and for computing suspended sand transport, McLean’s procedure of 1991 and 1992 is adopted. A bed-form classification scheme is developed that uses a particle size parameter and the transport strength to predict bed-form type; it correctly identifies 73% of the 1,192 mostly flume-scale calibration data sets. For 194 sets of dune-transition bed-form calibration data, a modified version of van Rijn’s 1984 bed-form geometry predictor yields a geometric average predicted to observed height ratio of 1.00. After calibration, the algorithm produces overall geometric averages of predicted to observed depth and predicted to observed transport of 1.00. For a verification data set of 855 observations, mostly from rivers and canals, the overall geometric averages of predicted to observed depth and transport are 0.87 and 1.14.

In their separate treatment method version of USTARS, the authors have presented a significant conceptual improvement over the technology used in GSTARS. As the authors point out, separate treatment of suspended and bed load allows use of the model in disequilibrium situations where deposition predominates, as in their reservoir and estuarine examples. In addition, the formulation is general and thus applicable both to equilibrium situations, where separate estimates of suspended and bedload are needed, as well as to disequilibrium situations, where erosion predominates. Furthermore, because it incorporates lateral dispersion and thus is capable of transferring suspended sediment from one stream tube to another, the separate treatment method version of USTARS is superior to GSTARS, which does not provide any such capability. However, perhaps because their examples primarily concern disequilibrium sedimentation, the authors have chosen an inappropriate version, (9), of the van Rijn (1984) expression to represent the reference level concentration Cek for the erosion of individual k size fractions of the bed sediment; this is the topic of the present discussion. The van Rijn (1984) expression for determining the reference concentration Ce at the base of the suspended load layer, at elevation a above the average streambed level, is

Two factors prevent the direct determination of the point spectrum of axial turbulence from a spectrum of the fluctuations in rpm values of the analog output of a rotary flow meter. The first of these is the effect of the finite size of the flow meter propeller, the second is the effect of its inertia. The finite size effect depends on the local turbulence structure and is characterized by an "efficiency factor" which in general can only be estimated. The effect of propeller inertia can be evaluated by linearizing the equation of motion of the propeller. From the resulting linear ordinary differential equation with constant coefficients, a transfer function for the linear system can be calculated. This transfer function makes it possible to calculate a spectrum of axial turbulence in which the velocity is averaged over the area of the propeller. Experiments in which propellers were oscillated sinusoidally while being towed through still water showed that the amplitude response function is approximately equal to that of a first-order system, while the phase function appeared to be independent of the natural frequency of the system.

The sampling system collects water-sediment samples at local stream velocity from any point in an open channel flow. The system uses a flow-through Pitot tube as a combination velocity sensor and sampler nozzle. The main advantage of the sampling system over existing suspended sediment samplers such as the US-P series samplers is that a sample of any desired volume can be collected without changing the position of the sampler nozzle. To compare the performance of the system with that of other samplers, suspended-sediment samples were collected from a flat-bed flow using the system, a US DH-48 sampler modified for point sampling, and a siphon sampler. On the basis of these samples, at the 99% confidence level, the relative percent difference between the concentrations of the samples from the system and the siphon sampler was between -5.45 and 4.45 and the relative percent difference between the concentrations of the samples from the system and from the US DH-48 was between -0.54 and 7.78.