Journal of Hydraulic Engineering

The influence of channel width on bedload capacity in river reaches of given slope, water discharge, and channel‐bed material is examined. The view that transport capacity is a decreasing function of width is shown to be dependent upon an invalid premise. A contrary view—that transport capacity increases as channel width increases—is also considered. Conclusions based on the second view are shown to be inconsistent with transport formulas or are restricted to channels at a near‐threshold state. The existence of an optimum width that maximizes capacity is demonstrated. This is a consequence of the nature of the relationship between bedload transport rates and flow intensity (notably a threshold condition) and of the relationship between flow resistance and depth. Expressions are derived for the optimum channel width and are shown to predict Gilbert's flume observations. Problems are considered in applying this approach to natural channels.

The complete hydrodynamic equations of the shallow‐water theory in one dimension are employed to compute the flood wave resulting from the total and instantaneous collapse of a dam in a broad rectangular channel. The MacCormack numerical scheme is employed to solve the system of flow equations in a conservation‐law form. The actual upstream and downstream boundary conditions of the flow field, i.e., a depth of flow equal to zero at these boundaries and beyond, are used for the solution of the flow equations. The results obtained are compared with computational and experimental data obtained by other investigators. The broad rectangular channel was employed for the purpose of comparing results. The method can easily be applied to channels of arbitrary cross‐sectional shapes, as well as to almost any other unsteady open‐channel flow problem by incorporating the appropriate initial and boundary conditions.

Einstein's bed load transport equation was modified for laminar overland flow under rainfall conditions. The modifications consisted of using a laminar velocity profile and a lift force calculated from the fluid drag force. The parameter λ was fitted from available experimental data. The results show improvement over the original Einstein equation. This sediment transport model was then coupled with an overland flow model and tested on data from a sand filled flume.

This paper presents the basic framework for a model that can be used to determine the optimal (least‐cost) design of a water distribution system subject to continuity, conservation of energy, nodal head bounds, and reliability constraints. Reliability is defined as the probability of satisfying nodal demands and pressure heads for various possible pipe failures (breaks) in the water distribution system. The overall model includes three that are linked: a steady‐state simulation model, a reliability model, and an optimization model. The simulation model is used to implicitly solve the continuity and energy constraints and is used in the reliability model to define minimum cut sets. The reliability model, which is based on a minimum cut‐set method, determines the values of system and nodal reliability. The optimization model is based on a generalized reduced‐gradient method. Examples are used to illustrate the model.

A submerged drop structure wherein the drop height is less than the flow depth in the channel is introduced. Fifteen tests were conducted to arrive at a structure which was the most economical to build and was hydraulically acceptable. It is concluded that in cases where numerous drop structures are needed for channel grade control, substantial cost savings can be realized by using shorter and smaller drop structures that are as effective as the larger conventional structures.