Abstract:
The present research investigates the numerical modelling aspects of unsteady flow in compound channels, with special interest in the "flood plain conveyance" aspects. This is examined through applications of three unsteady flow dynamic routing models: DWOPER, EXTRAN, and ONE-D to both laboratory and field data sets. In the context of applying DWOPER to the data sets three different approaches to define "off-channel" storage areas were considered. The first, which viewed the composite flow field as a single hydraulic unit without storage, produced significant differences between simulated and observed stage and discharge hydrographs. The second and third options separated the shallow and deep zones of the compound flow fields using different types of (imaginary) interface planes. The second option, which considered vertical interface planes, gave generally good results for the laboratory data but was less successful when applied to the field data. The third option used diagonal interface planes to define flood plain storage areas. The inclination of the diagonal plane to the horizontal ($\Theta$) was adjusted to reflect changing hydraulic conditions. The form of the simulated hydrographs using this particular approach was found to be sensitive to variations in $\Theta$. Statistical analyses were performed to determine optimum $\Theta$-values for a wide range of hydraulic conditions. Finally, an equation was developed to define the flood plain hydraulic boundaries.
