Evaluation of Flood Risk Factors in the Design of Highway Stream Crossings. Volume III. Finite Element Model for Bridge Backwater Computation.

摘要

A mathematical model describing the steady,two-dimensional subcritical flow in wide,heavily vegetated flood plains of bridge waterways has been developed using the finite element method of numerical analysis. The basic fluid equations comprising the model consist of the phenomenologic motion equations and the continuity equation,which are solved simultaneously by numerical methods to yield the spatial distribution of water surface elevations and velocities within the flow region for prescribing boundary conditions. The model simulates flow characteristics of arbitrary geometry. Hydraulic computations for various highway stream crossing orientations can be performed by the model. The model also simulates flow overtopping roadway embankments and performs hydraulic computations for a series of bridges across a stream valley without requiring prior assumption of the flow distribution for each bridge opening. The model has been tested for two example problems: a field site near Laurel,Mississippi,and for hydraulic flume data. In both examples good agreement between the model and the observed data was demonstrated.