TWO-DIMENSIONAL FINITE-ELEMENT HYDRAULIC MODELING OF BRIDGE CROSSINGS: RESEARCH REPORT. FINAL REPORT

This report presents the results of a 6-year project, conducted by the U.S. Geological Survey in cooperation with the Federal Highway Administration, to develop an accurate, efficient, easy-to-use finite-element surface-water flow model (FESWMS-2DH) for use in analyzing backwater and flow distribution at highway crossings of rivers and flood plains. When lateral variations in water-surface elevation and flow distribution are significant, a two-dimensional approach has advantages over a one-dimensional approach. The finite-element method (Galekin's method) is ideally suited to modeling two-dimensional flow over complex topography with spatially variable roughness and allows the user great flexibility in defining flow boundaries, channels, and embankments. A large number of alternative flow-equation formulations, interpolation and weighting functions, and schemes for solving the large systems of algebraic equations that arise in applying the finite-element method were tested during the project. Features added to FESWMS-2DH include weir flow (roadway overtopping), culvert flow, linear variation of Manning's n (roughness coefficient) with depth, simple and accurate handling of lateral boundaries, automatic network generation and refinement, and extensive error checking. Sections of the report are devoted to the application of FESWMS-2DH to data from the Geological Survey's Flood Plain Simulation Facility, the use and calibration of FESWMS-2DH, and the use of the model by the highway industry.