Shape Effects on Resistance in Flood-Plain Channels

For flow computation in flood plain channels, the flow cross section is usually divided into subsections to ensure hydraulic homogeneity. However, the question of whether or not to include the division lines as part of the wetted perimeter still remains unanswered. In this study, efforts have been made to determine division lines having zero shear stress so that they need not be included in the wetted perimeter. Laminar flow cases were solved to gain qualitative insight into the shape effects on resistance and location of division lines. For turbulent flows, division lines were determined from velocity distribution patterns; and resistance coefficients for both laminar and turbulent flows are lower than those in wide rectangular channels having the same boundary materials. New formulas are proposed for computation of discharge in both main-channel and flood-plain portions.