Two-dimensional (2D) hydraulic modeling of riverine systems continues to become more prevalent and widespread. The Federal Highway Administration (FHWA) also continues to advocate for 2D models as it relates to bridge scour evaluations and countermeasure design. However, in the USA, there are many river and stream systems modeled using 1D methods and these rivers are mapped as part of the Flood Insurance Program. FEMA is gradually transitioning to a greater use of 2D models, but almost all the current Effective maps and models are based on1D techniques. Therefore, to obtain the required approvals for proposed infrastructure, such as a new bridge crossing, continued use of a 1D model is typically necessary. On some recent projects, clients have requested that once the 1D model has been completed, a 2D model be prepared as a means of “verifying” the conclusions and basis of design resulting from the 1D analysis. The goal of this investigation is to identify and compare results produced by 1D and 2D models given a comparable geometry for a specific proposed bridge/roadway for which an engineering design has been completed or that is currently ongoing. Since the underlying computational algorithms are completely different, there is no expectation that the results would be identical. However, there are many variations of model set-up that can be tested. These include 1D steady versus 1D unsteady compared to 2D (unsteady), and bridges with single column bents, as examples. This information may be useful to local floodplain managers and other national and state agencies responsible for defining policies and procedures that govern floodplain studies regardless of whether a project is located within a FEMA mapped floodplain/floodway or not.
