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 are 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.
Accomplishment of the project objectives will require at least the following phases and tasks.
Task descriptions are intended to provide a framework for conducting the research. The NCHRP is seeking the insights of proposers on how best to achieve the research objectives. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objectives.
Task 1.Conduct a literature review of relevant research in order to identify the state-of-the-practice related to 2D hydraulic models and modeling practices for transportation related riverine settings. The review shall include published and unpublished research conducted through the NCHRP; FHWA; and other national, international, state, and pooled-fund sponsored research.
Task 2. Synthesize the literature review to identify the knowledge gaps for selection and application of Manning’s roughness values in 2D hydraulic models. Compare and contrast methodologies used to apply Manning’s roughness values by commonly used models. In addition, identify field and laboratory data sets to be used in the assessment of 2D hydraulic models. These gaps should be addressed in the proposed research or in the recommended future research as budget permits.
Task 3. Propose an analytical program, to be executed in Phase II, to achieve the project objectives. At a minimum, the analytical program shall include the following steps:
- develop and calibrate 1D hydraulic models,
- develop and calibrate 2D hydraulic models,
- propose 4 software packages for analytical modeling and validation,
- utilize the identified field and laboratory data set in the analytical modeling, and
- apply 1D and 2D models for transportation related riverine settings that include bridge and approach roadway embankments for the following scenarios:
- a range of river morphology, bed materials, overbank land cover, and stream gradients, and
- low flow and flood flows within the main channel and overbanks.
Task 4. Identify areas of the current AASHTO and FHWA manuals that will be modified in Phase III.
Task 5. Provide an annotated outline of the proposed guidelines including examples to demonstrate the application of the guidelines to be developed in Phase III.
Task 6. Prepare Interim Report No. 1 that documents Tasks 1 through 5 and provides an updated work plan for the remainder of the research. This report must be submitted no later than 4 months after contract execution. The updated work plan must describe the process and rationale for the work proposed for Phases II though IV.
Note: Following a 1-month review of Interim Report No. 1 by the NCHRP, the research team will be required to meet in person with the NCHRP project panel to discuss the interim report. Work on Phases II though IV of the project will not begin until authorized by the NCHRP. Phase I shall be limited to $40,000.
PHASE II—Analytical Program
Task 7. Execute the analytical program according to the approved Interim Report No.1.
Task 8. Provide a detailed description of every chapter and section of the proposed guidelines and complete a sample chapter of the proposed guidelines selected by NCHRP. This chapter should be publication-ready.
Task 9. Provide a list of examples, to be developed in Task 12, to illustrate the application of the proposed guidelines. The list of examples and related details shall be presented in a matrix format.
Task 10. Prepare Interim Report No. 2 that documents the results of Tasks 7 through 9 and provides an updated work plan for the remainder of the project. This report is due no later than 12 months after approval of Phase I. The updated plan must describe the work proposed for Phases III and IV.
Note: Following a 1-month review of Interim Report No. 2 by the NCHRP, the research team will be required to meet in person with the NCHRP project panel to discuss the interim report, if necessary. Work on Phases III and IV of the project will not begin until authorized by the NCHRP. Phase II shall be limited to $300,000.
PHASE III— Guidelines Development
Task 11. Develop the guidelines and propose modification to the AASHTO and FHWA manuals according to the approved Interim Report No.2.
Task 12. Develop the examples to demonstrate the application of the proposed guidelines.
Task 13. Prepare Interim Report No. 3 that documents the results of Tasks 11 and 12 no later than 7 months after approval of Phase II. The updated plan must describe the work proposed for Phase IV.
Note: Following a 1-month review of Interim Report No. 3 by the NCHRP, the research team will be required to meet in person with the NCHRP project panel to discuss the interim report, if necessary. Work on Phase IV of the project will not begin until authorized by the NCHRP. Phase III shall be limited to $100,000.
PHASE IV—Final Products
Task 14. Revise the draft guidelines and proposed modification to the AASHTO and FHWA manuals considering the NCHRP’s review comments. The revised guidelines and proposed modifications are due no later than 1 month after approval of Phase III.
Task 15. Prepare final deliverables including: (1) the guidelines, (2) propose modifications to the AASHTO and FHWA manuals, (3) the data set for all hydraulic modeling scenarios, (4) a final report that documents the entire research effort, and (5) a stand-alone technical memorandum titled “Implementation of Research Findings and Products.” See Special Note E for additional information.
Note: Following receipt of the draft final report, the remaining 3 months shall be for NCHRP review and comment and for research agency preparation of the revised final report. Phase IV shall be limited to $60,000.
STATUS: Research in progress - The research team requested a no-cost contract extension with a proposed completion of 05/31/2023