Bridge Hydraulic Analysis With Hec Ras

Most analyses of bridge hydraulics for flood flows are performed using the Army Corps of Engineers HEC-RAS (Hydrologic Engineering Centers River Analysis System) computer program. This study was carried out to compare results of HEC-RAS bridge modeling with experiments performed in a laboratory flume. The study was intended to add some insight into the effect of bridge hydraulic features such as ineffective flow regions, weir overflow and flow through skewed bridges. This insight should be useful for bridge engineers in HEC-RAS bridge modeling endeavors. A laboratory flume was constructed specifically for this project. The flume cross section has a main channel region and relatively wide left and right overbank regions. Different bridge scenarios were modeled. Froude number similarity was used to "scale up" model parameters and create prototype HEC-RAS hydraulic models simulating laboratory model conditions. Water surface profiles were compared for corresponding HEC-RAS and laboratory results.

Basic hydraulic considerations - Channel types and behaviour relation to bridges - Basic hydraulic requirements - Hydraulic design procedures Hydrologic estimates - Statistical frequency analysis - Runoff modeling - Empirical methods - High water levels and stage-discharge relations - Extreme floods and risk Scour protection and channel control - Scour protection around bridge foundations - Erosion protection of banks and slopes - Design of rock riprap - Cannel control works Hydraulic aspects of construction, inspection and maintenance - Construction - Inspection - Maintenance Special problems - Tidal crossings - Inland basic crossings - Waves and waves protection - Physical modeling of bridge problems - Alluvial fans - Debris flow and torrents

TRB's National Cooperative Highway Research Program (NCHRP) Report 653: Effects of Debris on Bridge Pier Scour explores guidelines to help estimate the quantity of accumulated, flow event debris, based on the density and type of woody vegetation and river bank condition upstream and analytical procedures to quantify the effects of resulting debris-induced scour on bridge piers. The debris photographic archive, the survey questionnaire and list of respondents, and the report on the field pilot study related to development of NCHRP 653 was published as NCHRP Web-Only Document 148: Debris Photographic Archive and Supplemental Materials for NCHRP Report 653.

The Kansas Department of Transportation (KDOT) and most bridge consultants in Kansas have been using the DOS-WSPRO program and the KDOT scour spreadsheets to perform bridge hydraulics and scour analysis for the past several years. Unfortunately, DOS-WSPRO is a DOS program that is no longer supported and there is no metric version. Consequently, the newer Windows-based hydraulics program HEC-RAS (Hydrologic Engineering Center River Analysis System) developed by the U.S. Army Corps of Engineers appears to be a logical choice to succeed DOS-WSPRO as the basic flow model in KDOT's bridge design and scour analysis program. HEC-RAS has gained considerable popularity in the engineering community and offers many options not previously available to hydraulic modelers. It also has a scour module and has an option, the WSPRO bridge analysis routine (henceforth called HR-WSPRO). This study compared the HEC-RAS program with the DOS-WSPRO program and examined the HEC-RAS program with regard to scour analysis. The possibility of using the existing KDOT scour spreadsheets with output from the HR-WSPRO bridge routine was also considered. Finally, a literature review was performed to determine if any updates in the scour methods and new approaches to special conditions, such as the effect of debris or pressure flow affecting pier scour, were available.