BACKGROUND

Hydraulic engineers have access to several hydraulic modeling software packages that can be used to analyze the hydraulics of bridge waterway crossings. Analysis can range from a simple analysis using a single cross-section and computed normal depth, to one-dimensional numeric modeling with multiple cross sections, to sophisticated two-dimensional numeric modeling. Flow rates used in the modeling can also vary in complexity from a single flow rate, to flow rates that vary along the river reach, to flow rates that vary with time.

Site conditions in conjunction with project objectives, complexity, and resources should dictate the type of numeric modeling software used to analyze a project. When a simple modeling approach will not accurately predict hydraulic conditions, hydraulic engineers must use a more sophisticated modeling approach. A current perception in numeric modeling is that complex approaches require an increase in design cost and time; however, this may not be true in many situations. Because hydraulic engineers do not always know the relative benefits associated with various modeling approaches, criteria and guidance are needed to help hydraulic engineers select the most appropriate modeling approach.

Currently, there is an emphasis on development and use of two-dimensional numeric models that produce more detailed and accurate analyses of river systems and bridge crossings. Until recently, the use of two-dimensional models required extensive field surveys and significant increases in personnel and computer resources compared with traditional one-dimensional approaches. With the advent of graphical user interfaces for two-dimensional modeling software and continued improvements in computer hardware, significant advances have been made in the ability to apply two-dimensional models to solve practical problems. However, very little information is available on the benefits of applying two-dimensional models. Research is therefore needed to define the conditions under which two-dimensional numeric models are warranted in the hydraulic analysis of bridge crossings in riverine and tidal systems.

OBJECTIVE

The objective of this research is to develop a decision analysis tool and guidelines to assist hydraulic engineers in selecting the most appropriate numeric modeling software for analyzing bridge openings in riverine and tidal systems.

Accomplishment of the project objectives will require at least the following tasks.

TASKS

PHASE I (1.) Conduct a literature review to identify commonly used one-dimensional and two-dimensional numeric modeling software that can be used in the analysis of bridge openings in riverine and tidal systems. Identify available data sets from actual bridge sites for use in analyzing the different modeling software. The data sets should include not only input data for the modeling software but also, if available, observed event data for use in validating the model results. Identify and characterize site conditions and design requirements that can affect the selection of a hydraulic model. (2.) Segregate the Task 1 data sets, site conditions, and design requirements into categories, including but not limited to embankment skew, skewed and/or complex pier configurations, complex floodplain geometry, curvilinear flow, valley slope, multiple openings, and variable flow rates. Additionally, categorize identified modeling software based on numeric approach, capabilities, and ease of use. (3.) Using theoretical data and commonly used numeric modeling software identified in Task 1, develop one- and two-dimensional conceptual numeric models to evaluate the effects of site conditions including but not limited to embankment skew, skewed and/or complex pier configurations, complex floodplain geometry, curvilinear flow, valley slope, multiple openings, and variable flow rates. (4.) Based on the results of Tasks 1, 2 and 3, develop a preliminary decision analysis tool (e.g. decision tree) for use by practicing engineers in selecting the most appropriate numeric modeling software for use in a given situation and design stage. (5.) Within 10 months of contract award, submit an interim report documenting the information developed in Tasks 1 through 4. The interim report shall contain, as a separate appendix, an updated work plan for completing Phase II of the research. Meet with the NCHRP panel to discuss the interim report, proposed data sets for use in Phase II, and the updated work plan. Work on Phase II will not begin until the interim report and updated work plan are approved by the NCHRP.

PHASE II (6.) Using the Phase I data sets agreed on during the interim meeting, validate the decision analysis tool for selecting the most appropriate numeric modeling software for use in a given situation and design stage. Revise and finalize the decision analysis tool as necessary based on the validation results. ( 7.) Develop guidelines to assist hydraulic engineers in applying the decision analysis tool. ( 8.) Submit a final report documenting the entire research effort. The report shall include an appendix that fully describes the decision analysis tool and guidelines and provides illustrative examples for use of each.

Status: Project completed.

Product Availability: The contractor's final report is available as NCHRP Web-Only Document 106.