This paper addresses the recent trend in fluvial geomorphology towards
using computational fluid dynamics to explore the adjustment between
Row processes, sediment transport and river channel morphology. It aims
to evaluate the extent to which three-dimensional (3D) models improve
predictive ability and prediction utility compared to two-dimensional
(2D) applications. This is achieved through comparing the predictions
of both 3D and 2D models with high-quality field data. Identical
boundary conditions, obtained from a confluence within a gravel-bed
river system with high relative roughness, are defined for each model.
Evaluation of the 3D model suggests that there is a fundamental
limitation upon model predictive ability due to problems of specifying
topographic complexity. However, comparison with the 2D model shows
that the 3D model has a higher predictive ability, particularly if the
2D model is not corrected for the effects on flow structure of
secondary circulation. Further, the 3D model provides more reliable
estimates of bed shear stress and other more useful information, such
as the three-dimensional flow field important for mixing processes.
This suggests that there is significant merit in the move towards 3D
models, but that research is required to incorporate methods developed
in other fields for dealing with boundary condition uncertainties. (C)
1999 Elsevier Science B.V. All rights reserved.