The National Academies

NCHRP 24-49 [Completed]

Guidelines for Selection and Application of Manning’s Roughness Values in Two-Dimensional Hydraulic Models

  Project Data
Funds: $495,254
Research Agency: Penn State University
Principal Investigator: Dr. Xiaofeng Liu
Effective Date: 8/21/2020
Completion Date: 5/31/2023
Comments: The Final Report will be published as NCHRP Report 1077

Measures to improve the accuracy, reliability, and consistency in selecting roughness values for the application of two-dimensional (2D) hydraulic models at highway crossings and in transportation corridors will represent a major step forward in the evolving state of practice. Some state departments of transportation (DOTs) have readily embraced the application of 2D models for transportation facility planning, analysis, and design; other states have held back and taken a more wait and see approach as the tools and techniques have continued to advance.
At present, whether a one-dimensional (1D) or a 2D modeling approach is taken, inconsistencies can exist from state to state, and even within states at the various district levels, on how to develop accurate and reliable hydraulic models. The fundamental issue is the selection and assignment of Manning’s roughness values for a variety of channel types and land uses in the overbank floodplain areas.   Manning’s roughness values along with channel and floodplain geometry (i.e., topographic and hydrographic surface data) are recognized to be the two most important components for developing and calibrating hydraulic models.
Identifying feasible, cost effective, and consistent guidelines to improve the state of the practice in selecting roughness values for hydraulic modeling is highly desirable. The potential payoff to owners of transportation assets, in particular roadways, bridges and culverts, is significant if the accuracy and reliability of hydraulic models can be improved. Therefore, definitive and detailed guidelines on proven hydraulic modeling is needed to improve the state of practice on a national level and in the rapidly advancing field of 2D hydraulic models.
The objectives of this research were to (1) develop guidelines for selection and application of Manning’s roughness values in 2D hydraulic models for transportation related riverine settings and (2) propose modifications to the AASHTO Drainage Manual, the Federal Highway Administration (FHWA) Hydraulic Design Series (HDS) Number 7: Hydraulic Design of Safe Bridges, and the FHWA’s Every Day Counts (EDC) 2D Hydraulic Modeling Reference Manual (the EDC Manual will be available for the research team after the contract award). Herein, both FHWA HDS -7 and EDC manual are referred to as FHWA manuals.

STATUS: The final report will be published as NCHRP Research Report 1077.

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