On noninertia wave versus diffusion wave in flood routing

This note intends to address a misnomer in flood routing. The noninertia wa ve, which ignores both local and convective inertia terms in the momentum e quation, is a simplification to the full dynamic wave. While the diffusion wave refers more generally to the wave whose induced disturbance in flow is analogous to the diffusion of particles or heat. For the purpose of clarif ication, these waves are mathematically formulated and physically interpret ed. It is demonstrated that the diffusion wave can be mathematically formul ated from different levels of shallow water wave approximations with the as sumption that the celerity and coefficient of hydraulic diffusivity are ste p-wise constants. Both the linear and nonlinear perspectives of waves are d iscussed. The noninertia wave is demonstrated to be one of the special case s of the diffusion wave. (C) 2001 Elsevier Science B.V. All rights reserved .