Journal of Hydraulic Engineering

The characteristic changes in the boundary shear stress field of a channel bend at the intersection with a side overflow are investigated in this paper. On the basis of a field survey on bottom topography changes of the meandering river Allan Water at the cut-off section, a detailed study of boundary shear stresses in an idealized rigid bed model was undertaken. Both mathematical and experimental approaches were employed in the idealized model study. The analysis of results showed that continual reductions in shear stresses occurred in the bend at the side overflow region. The maximum reduction of shear stresses was 37% in cases of low side overflows and 82% in cases of high side overflows. These reductions were attributed to the development of stagnation and separation zones at the intersection associated with strong lateral outward currents. Based on the idealized model study, the features observed in the bed topography of Allan Water at the cutoff section are most likely to develop in cases of combined bend and high side overflows.

A new approach for predicting alluvial-channel resistance in the framework of the familiar Manning equation is proposed. The new method proposes a relation for the Manning coefficient that incorporates directly the role of bed configuration in determining alluvial-bed resistance. A relation for bed-form height is developed, which is then used as an independent variable to account for the resistance due to bed-form drag. The method was applied to a large body (969 flows) of river and flume data with satisfactory agreement with the observed values. Mean normalized errors for predicted flow depths and velocities were about 10% for all 969 flows. The procedure can be applied to natural streams with compound channels, since variable roughness for the main channel and overbank sections can be computed separately in this approach. Prediction accuracy was generally better for flows that were clearly in the lower regime (ripple or dune) or in the upper regime (flat bed or antidune), but larger errors were associated with flows that were in or close to the transitional bed regime. It is hoped that future research will focus on flow processes and bed-form geometry during transition regime.

The maximum velocity in a channel cross section is highlighted with respect to its information content and relation to the mean velocity and entropy parameter. Under a wide range of discharge and water depth, a channel section seems to have propensity to establish and maintain an equilibrium state that corresponds to a value of entropy parameter. The entropy parameter of a channel section can be determined from the relation between the mean and maximum velocities. A technique has been developed to determine the discharge from a velocity profile on a single vertical passing through the point of maximum velocity in a channel cross section. The technique is an efficient way to estimate the discharge in streams and rivers, that can be used to continuously update the flow resistance during an unsteady flow, to enhance a filtering scheme designed to reduce uncertainties in flow forecasting. The use of the constant value of entropy parameter predetermined for a channel section can simplify the discharge estimation.

Accurate peak discharge estimates are important when sizing highway culverts to prevent possible flood damages and to ensure economic design. The purpose of the undertaken study was to find the most acceptable peak-discharge-estimation method for use on small agricultural watersheds in Nebraska. An analysis of time of concentration t _c methods was undertaken because of this parameter's importance in many peak-flow methods. Seven t _c equations were compared to recorded t _c values from four watersheds each less than 2 sq mi (5.18 km ²) in area. Field t _c values were derived from a hyetograph-hydrograph analysis. Six peak-flow methods were then compared to the recorded peaks and historical records to find the best estimation method. Based on three storm seasons of data, a modified form of the Kirpich equation and the U.S. Soil Conservation Service average-velocity equation estimate the time of concentration adequately. Peak discharges were most closely predicted using statewide regression equations, the Fletcher method, and the rational method. Results for the 25-year event (culvert design event) tentatively support the use of statewide regression equations.

An integrated hydrometeorological system for flow forecasting has been designed and implemented for real-time use in an operational environment at the U.S. Army Corps of Engineers Rock Island District, Illinois. The system operates routinely with data collected by real-time data-collection platforms and stored in a real-time database. Forecasts are based on coupled hydrological and meteorological models, and a state estimator that updates system states in real time using all current data. Five soil-water models are used to estimate rainfall abstractions: a generic API model, the modified Sacramento soil moisture accounting model, and three soil-water options in the HEC-1 model. Initial sensitivity analysis of the short-term system forecasts with respect to the soil-water model and the state-updating components indicates robust system behavior in short-term real-time flow prediction. In addition, sensitivity analysis shows that when updating is performed using all available operational data, the differences in results among soil-water models are small. Thus, selection of a soil-water model to estimate hydrologic abstractions may be based on user familiarity with a certain model and the estimation of its parameters.

Flood estimation models are often used to predict design floods of a selected average recurrence interval (ARI) using rainfall information of the same ARI. That is, they are used for probabilistic purposes rather than for forecasting during actual events. Design values of model parameters need to be derived in a manner corresponding with the way the models are applied in design. Design values of the main parameter of two simple flood estimation models, the rational method (runoff coefficient) and the United States Soil Conservation Service (USSCS) method (curve number), were derived for 105 small agricultural catchments in and around south east Queensland, Australia. These were obtained by reversing the way the models are used in design flood estimation, utilizing frequency analyses of rainfall and flood data. The derived values were considerably different from conventional handbook values; the latter gave inaccurate estimates of design runoff and flood peaks. The values derived from observed data were only weakly related to catchment characteristics including land use and soil type, but were regionally consistent. ARI and the method of estimating design rainfall duration had greater influences on the values derived.

Pipe flow is preferred for the bulk transport of granular materials as it is both economical and reliable. It finds application in the transport of minerals, especially ocean minerals, carried in water suspension and the transport of food grains carried in air suspension. The disposal of solid waste through pneumatic pipes is also gaining importance. Although the necessary equations for sediment transport through pipes are available, design equations have not been attempted as yet. In this paper a sediment-carrying pipeline design has been formulated as a geometric programming problem with a single degree of difficulty. The solution of the problem yields the optimal design having flow at the limit deposit velocity.