A three-dimensional unsteady method for simulating river flows

Natural river flows are mostly unsteady in nature due to seasonal variation of flow discharge and controlled operation of hydraulic structures. Often this unsteadiness leads to complex flow pattern changes and the flow characteristics may be quite different from that of steady-state flows. Unsteadiness is particularly important during flooding events and when submerged islands exist immediately upstream or downstream of hydraulic structures. In the past, however, unsteadiness has not been modeled in most projects involving fully three-dimensional computational fluid dynamic modeling. The purpose of this paper is to address the issue of unsteadiness in the context of fully three-dimensional numerical modeling. Particularly, effort is directed at developing the unsteady capability associated with the wetting and drying processes for a reach of a natural river. Validation and application were performed with a forebay reach of the Columbia River at the Rock Island Dam. The computational results are reported and discussed. Copyright ASCE 2004.