10.4122/1.1000000642
HUANG, GUOBIAO
GUOBIAO
HUANG
guobiao2002@yahoo.com
Yeh, Gour-Tsyh
Gour-Tsyh
Yeh
gyeh@mail.ucf.edu
HUANG, GUOBIAO
GUOBIAO
HUANG
guobiao2002@yahoo.com
An Integrated Media, Integrated Processes Watershed Model – WASH123D: Part 2 – Simulating surface water flows with different water wave models
XVI International Conference on Computational Methods in Water Resources
2006
2006
The complete Saint Venant equations/2-D shallow water equations (dynamic wave
equations) and the kinematic wave or diffusion wave approximations were implemented
for 1-D channel network flow and 2-D overland flow in a watershed model, WASH123D.
Careful choice of numerical methods is needed even for the simple kinematic wave
model. Motha and Wigham (1995) reported numerical oscillation in Galerkin finite
element of kinematic wave overland flow. Since the kinematic wave equation is of
pure advection, the backward method of characteristics is used for kinematic wave
model. A characteristic based finite element method is chosen for the hyperbolic-
type dynamic wave model. And the Galerkin finite element method is used to solve the
diffusion wave model.
Diffusion wave and kinematic wave approximations are found in many overland runoff
routing models. The error in these models has been characterized for some cases of
overland flow over simple geometry (e.g. Ponce 1978; Singh 2000 and Parlange 1990).
However, the nature and propagation of these approximation errors under more complex
2-D flow conditions are not well known. These issues are evaluated within WASH123D
by comparison of simulation results on several example problems. The accuracy of the
three wave models for 1-D channel flow was evaluated with several non-trivial (trans-
critical flow; varied bottom slopes with frictions and non-prismatic cross-section)
benchmark problems (MacDonnell et al., 1997). The test examples for 2-D overland
flow include: (1) a simple rainfall-runoff process on a single plane with constant
rainfall excess that has a kinematic analytical solution under steep slope
condition. A range of bottom slopes (mild, average and steep slope) are numerically
solved by the three wave models and compared; (2) Iwagaki (1955) overland flow
experiments on a cascade of three planes with shock waves; (3) overland flow in a
hypothetical wetland (infiltration bed). The applicability of dynamic-wave,
diffusion-wave and kinematic-wave models to real watershed modeling is discussed
with simulation results from these numerical experiments. It was concluded that
kinematic wave model could lead to significant errors in most applications. On the
other hand, diffusion wave model is adequate for modeling overland flow in most
natural watersheds. The complete dynamic wave equations are required in low-terrain
areas such as flood plains or wetlands and many transient fast flow situations.