Estimating the discharge capacity of doubly sinuous compound channels

With the increased emphasis on more environmentally appropriate drainage and river channel design, new techniques must be developed to allow designers adequately to assess the discharge capacity of these systems. Unlike the more traditional channel designs that were typically straight and prismatic in cross-section, the modern view of an environmentally and aesthetically pleasing channel is one which is compound in cross-section and, typically, meandering. This paper describes a discharge estimation technique which may be used to calculate the discharge capacity where both the main channel and the flood plain are meandering. This type of channel has been previously termed a ‘doubly sinuous compound channel’ by the authors. A technique for determining the average cross-sectional properties and channel slope for a particular reach is described in this paper, which allows traditional uniform flow resistance equations like the Manning equation to be applied. An experimental programme was undertaken at HR Wallingford and provided valuable insights into this complex flow phenomenon. It was found that the commonly used vertical division of the compound channel at the edges of the main channel was much less satisfactory than a horizontal division across the top of the main channel. The reasons for this are outlined in the paper.