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Trapezoidal open channels are designed for specified slope, specific lining materials, and for a specified design flow. These input design parameters are prone to uncertainties. The freeboard is used to confine the flow within the limits of the channel cross section and to accommodate the uncertainty effects. Because of the size of uncertainty, the flow can overtop the freeboard with a 'flooding probability.' To design an optimum channel cross section for safety against overtopping, the flooding probability constrained optimum channel design concept is introduced. An optimization model was developed which has two objective functions of minimizing the total cost of the channel and minimizing the flooding probabilities subject to uniform flow equation as constraint. The constraint method of multiobjective optimization is used in which the objective of minimizing the flooding probability is converted to a constraint, and the resulting single objective optimization problem is solved. The flooding probability constraint is developed by using the first order analysis. The final single objective optimization model is highly nonlinear and requires the use of the projected augmented Lagrangian technique. The optimization model is applied for two cases, namely, channels having composite roughness and channels having uniform roughness. The solution results of the analysis established the potential of the model. DOI: 10.1061/(ASCE)0733-9437(2007)133:1(53) CE Database subject headings: Open channels; Roughness; Floods; Optimization; Lining.

A one-dimensional model has been established to simulate the fluvial processes under dam-break flow over movable beds. The hydrodynamic model adopts the generalized shallow water equations, which consider the effects of sediment transport and bed change on the flow. The sediment model computes the nonequilibrium transport of bed load and suspended load. The effects of sediment concentration on sediment settling and entrainment are considered in determining the sediment settling velocity and transport capacity. In particular, a correction factor is proposed to modify the Van Rijn formulas of equilibrium bed-load transport rate and near-bed suspended-load concentration for the simulation of sediment transport under high-shear flow conditions. The governing equations are solved by an explicit finite-volume method with the first-order upwind scheme for intercell fluxes. The model has been tested in two experimental cases, with fairly good agreement between simulations and measurements. The sensitivities of the model results to parameters such as the sediment nonequilibrium adaptation length, Manning's roughness coefficient and the proposed correction factor have been verified. The proposed model has also been compared to an existing model and the results indicate the new model is more reliable. DOI: 10.1061/(ASCE)0733-9429(2007)133:1(48) CE Database subject headings: Dam failure; Flood routing; Sediment transport; Suspended load; Bed load; Erosion; One-dimensional flow; Shock waves.

Experimental measurements using a laser Doppler anemometer (LDA) system have been performed on 150 [micro]m dense glass particles in a fully developed downward channel flow in air. Tests were conducted in smooth, rough development, and fully rough wall conditions with a channel Reynolds number of 13,800, corresponding to a centerline gas phase velocity of 10.5 m/s with a dilute loading of particles of 15% by mass fraction. Velocities were measured and statistics compared to see the nature of the effects of the wall roughness in a rebuilt channel facility originally used for important works including Kulick, Fessler, and Eaton, (1994, 'Particle Response and Turbulence Modification in Fully-Developed Channel flow,' J. Fluid Mech., 277, pp. 109-134) and Paris (2001, 'Turbulence Attenuation in a Particle-Laden Channel Flow,' Ph.D. thesis, Stanford University, Stanford, CA). Wall roughness has a substantial impact on gas phase mean velocities across most of the channel width, except very near the wall. The turbulence intensity of the gas phase is enhanced across the entire channel in the presence of fully rough walls. The rough walls have an even greater impact on the particle phase. Streamwise particle velocities are reduced up to 40%, and become quite uniform across the channel. Particle fluctuating velocities are nearly doubled near the channel centerplane. Profiles appear uniform, due in large part to strong transverse mixing induced by particle-wall collisions. Much of the data of Kulick and Paris is shown here to be strongly influenced by wall conditions with poorly defined roughness in the development region, followed by rapid flow recovery in a relatively smooth test section. [DOI: 10.1115/1.1891149]

The motion of conservative 2D thermals on beds with slope angles [Theta] ranging from 5 to 90 [degrees] is investigated theoretically and experimentally. Using a large number of experimental data, important flow characteristics, including the shape factors, spatial growth rate, propagation speed, and entrainment coefficient, are quantified as functions of bottom slope angles. A thermal model, which includes a resistance term, is developed. It is found semiempirically that resistance coefficients [C.sub.d] are almost independent of [Theta] and the values of [C.sub.d] are in the range of 0.4-0.6. Capability of the model is demonstrated by comparing numerical results with theoretical as well as experimental results.

Streamflows have a direct dependence on precipitation and these are directly linked to climate. Then, in this paper the temporal climatic variability in the 'Rio de la Plata' Basin is analysed through the changes in the river's discharges. These are the reflection of the climatic inputs areally integrated, and in consequence, contain more information on climate variability than that provided by the scarce punctual records of precipitation and temperature. The time series of streamflows correspond to monthly and annual means in stations selected in the basin for the period 1931-1992. However, in the present paper, the period 1901-1992 was considered in all cases whenever possible. The following changes and tendencies in the flow series were detected: 1. An important change of tendency between 1970 and 1972, and another not so significant before that date were detected in 1917-1918 and 1943-1944. 2. The jumps in the means in several sub-periods were detected using different methods. They showed jumps mainly in the period 1970-1972 in the annual streamflows series. The jumps in the annual streamflow series consist of an abrupt change in climatic variables affecting temporarily the averages of such variables during a certain period of time (years). The results are consistent with the conclusions obtained by other authors for the same region, both in precipitation and in the general circulation of the atmosphere. Keeping in mind this analysis of the series of streamflows, indicators of normal variability of tendencies relative to natural regional causes were detected, although the local causes were not anthropogenically analysed, and so no other manifestations of randomless in the zone of the Basin under study because of the lacking of data.

A coupled physical and biological model was used to investigate the biological and physical mechanisms that control the primary production and plankton patches near the coast and within the low-salinity frontal zone in the near Louisiana-Texas (LATEX) shelf. The model showed that the tidal mixing was too weak to make a significant contribution to the basic distribution of biological production within the frontal zone over the inner LATEX shelf.

The application of the Muskingum model to river and channel flood routing may have some limitations because of its inherent assumption of a linear relationship between channel storage and weighted flow. Although nonlinear forms of the Muskingum model have been proposed, an efficient method for parameter estimation in the calibration process is still lacking. In this paper, the objective approach of genetic algorithm is proposed for the purpose of estimating the parameters of two nonlinear Muskingum routing models. The performance of this algorithm is compared with other reported parameter estimation techniques. Results of the application of this approach to an example with high nonlinearity between storage and weighted-flow, show that the genetic algorithm approach is efficient in estimating parameters of the nonlinear routing models. A supplementary analysis of the sensitivity of the parameters during the performance of genetic algorithm shows that a unique set of parameters exists that would result in the best performance for a given problem. In addition, genetic algorithm does not demand any initial estimate of values of any of the parameters, and thus avoids the subjectivity and computation time associated with the traditional estimation methods.

Outflow hydrographs for three dams with long lakes in narrow valleys were computed by both hydrologic routing (level-pool routing) and hydraulic routing. They were compared with three inflow hydrographs of different peaks with three unregulated ogee spillways of different capacities. In all these cases, the difference between outflow hydrographs was greatest at the peak value, growing larger as the spillway capacity became smaller, relative to the magnitude of the inflow hydrograph. The peak outflow by hydraulic routing was smaller than that by hydrologic routing for all the routing combinations, the difference varying between 2 and 11%.

This investigation presents a spectral method for solving the one-dimensional shallow-water wave equations. The spectral method is based on the Chebyshev collocation technique and finite-difference time stepping. The spectral method and finite-difference Preissmann scheme are applied to route a log-Pearson Type III hydrograph through a wide rectangular channel, and the results are compared. The spectral method performs better than the Preissmann scheme as long as the time-stepping errors are kept low. However, for larger time steps, the Preissmann scheme, which is almost second-order accurate in time (and second-order accurate in space) performs better than the spectral scheme, which is first-order accurate in time and has so-called infinite-order accuracy in space. This seems to indicate that the order of accuracy in time discretization is more important than that in space discretization, in numerical models, for fast-rising floods and friction-dominated flows.

A flow-duration curve (FDC) is simply the complement of the cumulative distribution function of daily, weekly, monthly (or some other time interval of) streamflow. Applications of FDCs include, but are not limited to, hydropower planning, water-quality management, river and reservoir sedimentation studies, habitat suitability, and low-flow augmentation. Although FDCs have a long and rich history in the field of hydrology, they are sometimes criticized because, traditionally, their interpretation depends on the particular period of record on which they are based. If one considers n individual FDCs, each corresponding to one of the individual n years of record, then one may treat those n annual FDCs in much the same way one treats a sequence of annual maximum or annual minimum streamflows. This new annual-based interpretation enables confidence intervals and recurrence intervals to be associated with FDCs in a nonparametric framework.

A new flood-routing method is compared with the DWOPER model. The new method combines a noninertia (or diffusion model) simplification of the de Saint Venant equation with a statistical procedure. It accounts for the nonlinearity and dispersion of the flood-wave propagation phenomenon. It also accounts for nonuniform lateral flow. The new method, unlike most hydrologic routing methods, can be used to simulate a variety of low variables such as water stage, depth, or discharge. The comparison is not only based on the accuracy of both models, but also, and mostly, on their practicality. Both models are compared for accuracy and in aspects such as data requirement, computer running time, actual time needed for calibration.

A method for selecting a sediment-transport formula for mathematical modeling of a specific gravel stream is described and illustrated with an example. This method is based on the measured changes in stream morphology instead of site-specific gravel transport data. In the approach, several transport formulas are tested based on their applicabilities in simulating stream-channel changes. It is the working hypothesis that a sediment formula suitable for mathematical application should generate stream-channel changes that can be substantiated by measurements. For Stony Creek in California, the Meyer-Peter Muller, Yang, Parker, and Engelund-Hanson formulas were tested separately. Sediment deliveries obtained using the Yang and Parker formulas are more or less similar. Simulated erosional and depositional changes are also similar and compare favorably with the measurements. The Meyer-Peter Muller formula predicted lower transport rates while the Engelund-Hanson formula produced higher transport rates. On the basis of the tests, the Yang formula and Parker formula were selected for Stony Creek applications.

A downstream control algorithm for on-demand operation of irrigation canal systems is presented. A constant water level is maintained at the downstream end of the pool. The approach is based on an explicit finite-difference solution procedure of the St. Venant equations. The upstream gate settings are corrected according to the water level and the flow rate at the information nodes along the canal. The method is illustrated for the control of a canal pool bounded by an upstream gate and a downstream gate or pump. The effectiveness of the control has been tested using an unsteady-flow simulation model that is based on the complete St. Venant equations and the implicit Preissmann scheme. The simulation results show that the proposed control method can cope with rapid variations of water demand and unknown disturbances in the system. The influence of the number of information nodes and the assessment of the physical parameters of the system on the response of the system has been investigated. Unless the estimated physical parameters of the system are too far from their actual values, an effective control can be achieved by measuring the water level and estimating the flow rate only at the most upstream and downstream ends of the pool.

The utilization of the mass-transport equation for the solution of advection, which are relevant for engineering problems due to mixing in natural streams, limits the required data to geometric and longitudinal-velocity information for each transect. The steady-state-concentration distributions can be determined using an input-concentration profile, geometric information for each transect and total river-flow rate.

Velocity measurements carried out in a rectangular laboratory flume having a gravel bed are presented. The measurements are carried out for four different bed shapes, characterized from different concentrations of coarser elements, and for the two conditions of small- and large-scale roughness. The analysis showed that the Dean profile is usable to establish the velocity profile for both hydraulic conditions. For small-scale hydraulic condition an indirect estimate procedure of the coefficients of Dean profile is proposed.

Shear stress is a fundamental parameter in many sediment transport expressions. It is commonly estimated from information contained in the velocity profile, specifically, shear velocity, u(sub *), and roughness length, zeta(sub 0). Under ideal conditions, the functional relationship between elevation above the bed and flow velocity is log-linear, as expressed by the 'law of the wall.' Unless the field data conform exactly to this ideal relationship, there is uncertainty in estimates of u(sub *) and zeta(sub 0) derived from velocity profiles. This uncertainty depends on the degree of scatter or deviation from the assumed log-linear model. Expressions are presented to quantify the error and to correct for it. Guidelines are suggested to minimize potential uncertainty, especially with regard to instrument deployment and velocity profile analysis. Calculation of confidence intervals around estimates of u(sub *) and zeta(sub 0), as proposed by Wilkinson (1984), is necessary and recommended.

Stream channel changes are often assumed to propagate downstream of the disturbed or urbanized reach, especially where the main controlling variables of discharge and sediment load vary regularly in the downstream direction. A survey of bankfull cross-sectional sizes at 10 stations along a tropical stream shows that downstream propagation of the disturbance may not always occur. Serial regression analysis suggests that a reduction in channel size induced by urbanization did not extend beyond the urbanized reach. Furthermore, local channel change did not alter the downstream log linear trend between channel size and basin area. Apparently, the storage of floodwaters and sediments on floodplains reduced the downstream effects of urbanization. Key Words: urbanization, downstream channel size, downstream propagation, impacts.

Bryan's (1989) model is used in this study to simulate the circulation in the Black Sea. Wind stress, heat exchange, precipitation and evaporation at sea surface are prescribed from climatic data. River inflow and the inflow from the Mediterranean Sea are taken from observations. Two types of models are discussed: GCM with horizontal resolution [delta][lambda] = 1 [degree], [delta][phi] = 0.5 [degree] and 12 levels; and EGCM with horizontal resolution [delta][lambda] = 20', [delta][phi] = 10' on the same levels. GCM is designed to study the role of the wind and buoyancy fluxes for the establishment of circulation. Model data shows that in the baroclinic experiments kinetic energy is less than in the barotropic experiment. This is a consequence of the formation of a strong halocline in the upper layer, where a substantial part of the energy input transforms into potential energy. The specific vertical stratification in the Black Sea restricts the penetration of seasonal signal into deep layers, and preconditions the establishment of a cold intermediate layer. Model data from EGCM shows that eddies contribute to some change in the transport mechanisms, compared to those in GCM. Seasonal forcing affects substantially the variability of the main Black Sea gyre. Comparisons between model and observational data indicate that models resolve the main features of the Black Sea circulation. They illustrate correctly physical processes in strong stratified geophysical fluids, and particularly in semi-enclosed basins, where precipitation and runoff exceeds evaporation.

Critical depth is an important parameter in the analysis of varied flow in canals and natural streams. For triangular, rectangular, and parabolic channel sections it is possible to express critical depth analytically. However, for many practical sections, including the trapezoidal section, the governing equations are implicit in the critical depth. For these sections the critical depth is presently obtained either by trial and error procedure, or by using empirical equations based on curve fitting. In this Technical Note exact analytical solutions of critical depth for the trapezoidal open channel section have been obtained in the form of fast converging infinite series. DOI: 10.1061/(ASCE)0733-9437(2005)131:5(474) CE Database subject headings: Canals; Water depth; Critical flow; Open channels; Streams; Energy.

An earlier proposed 2D friction slope correction model is believed to be ineffective and inconsistent with its other claims regarding 1D and 2D friction slope equations for flow in channels with vertical sidewalls and free-slip boundaries. As a remedy for 2D modeling problems for depth-averaged flow, Manning's uniform flow formula should be used with boundary layer concepts and the Reynolds stress distribution to effectively show the concave and convex forms for open channel flows.

The study on the National Weather Service simplified dam break (SMPDBK) model by A. Paquier and O. Robin is problematic. The researchers did not provide information to support their findings that the SMPDBK model is not suitable for engineering purposes because it yields errors of >100% in water depths. The study was also vague as to whether the CASTOR model calculates the peak discharge at the dam or if it is used as an input parameter.

An existing hydraulic model is modified to predict stage-discharge curves for channels with nonuniform cross sections, sand and gravel-bed materials, and flexible or nonflexible riparian vegetation. The model is based on a version of the flow momentum and continuity equations that account for lateral shear. The model accounts for the effects of vegetation using empirically calibrated flow resistance equations that incorporate measurable physical properties of vegetation. Separate flow resistance equations are used for flexible and nonflexible vegetation types. Simulated stage-discharge curves are compared with data obtained from three natural river channels. Discrepancies between simulated and observed data range between 2 and 45%, but most ([approximately]70%) discrepancies were