Numerical simulation of flow in compound channels*

Michael L. MacWilliams, Robert L. Street, and Peter K. Kitanidis

Compound Channels are often constructed in restoration projects on streams that have been channelized or are deeply incised. The compound channel design allows for flow over a wider cross-sectional area and is supposed to reduce flow velocities and bed shear stresses in the channel during high flow events. The reduction in channel velocities helps to reduce further incision and establish a more natural flow regime under high flow conditions.

In river restoration projects, compound channel designs are often based on one-dimensional numerical simulations. However, one-dimensional numerical models are not always suitable for simulating the complexity of compound channel flows and can produce erroneous results. We will present a comparison of simulation results for a pre-restoration incised channel and a post-restoration compound channel using one-dimensional and three-dimensional numerical models. We will focus on the limitations associated with these models and address their suitability for use in the design of compound channels in river restoration projects.

* MacWilliams, M. L., R. L. Street, and P. K. Kitanidis, Numerical Simulation of Flow in Compound Channels, EOS Trans. AGU, 83(47), Fall Meet. Suppl., Abstract H72B-0852, 2002.