Best Hydraulic Section of a Composite Channel

Abstract

The half-circle is the ideal shape of the best hydraulic section of open channels, but semicircular channels are not practical to construct. The semicircular section is approximated by a composite section that is composed of a trapezoidal section at the bottom and a rectangular section at the top. Such a composite channel can be easily constructed in rocks. This technical note presents an analysis for determining the channel proportions that yield a minimum wetted perimeter for a given flow area of the composite channel. The results of the analysis show that the best hydraulic section has the shape of a half-octagon for composite channel and a composite section is more efficient than a trapezoidal section.