Quantitative Modeling Tools of Scour and Morphological Impact due to Large Wood Debris Structures

Project ID: 4495
Principal Investigator: Yong Lai
Research Topic: Sediment Management and River Restoration
Funded Fiscal Years: 2014, 2015 and 2016
Keywords: large wood dedbris; 3d modeling tools; scour; morphology

Research Question

Large wood debris (LWD) has been identified as a priority research area in the FY 2013 Reclamation Science and Technology (S&T) program as a result of the 2012 LWD Workshop sponsored by Reclamation S&T Office and US Army Corp of Engineers (USACE). Particularly, numerical model prediction of the resultant scour and morphological impacts due to LWD was singled out as one of the highest priority groups by the workshop. A scoping study was funded by S&T in FY 2013 on developing quantitative modeling tools of morphological impact by LWD. With the successful completion of the scoping study, we seek to move forward to a full-proposal level study in FY 2014.

Methods or guidelines do not exist for predicting responses from the construction or natural build-up of LWD. The existing scour estimation methods are limited to a few specific in-stream structures such as bridge piers; they are mostly empirical in nature. Even with the traditional scour methods, they mostly rely on flume data. In recent years, however, accurate scour and morphological predictions are becoming feasible with the availability of the state-of-the-art multi-dimensional numerical models. These tools have not been evaluated at Reclamation for LWD, but they were identified at the LWD Workshop to have great potential to become the primary quantitative prediction tools for LWD-generated scour and morphological impact.

The FY 2013 S&T funded scoping study found that it is technically feasible to adopt the current state of the art modeling tools for scour and morphological predictions with LWD. The proposed study will answer the following specific questions:
(1)Can the selected multi-dimensional models be used reliably and accurately to assist LWD design and the scour and morphological change related risk assessments?
(3)Can the model generated data help develop design guidelines?
(2)Can the selected models be improved so that they may be used by engineers with ease in a desk top computing environment?

Need and Benefit

Large Wood Debris (LWD) structure has been widely used at several Reclamation regions for river restoration. LWD structures have a permeable body that can significantly reduce local scour and the material is locally available and cheaper in a remote mountain area. Woody structures are also natural habitat for aquatic life. Its use, however, has been challenged due to a lack of general design guidelines that address the risk, safety, and morphological impact. The 2012 LWD workshop sponsored by Reclamation S&T and USACE has identified the need (a) to produce design guidelines and (b) to use more advanced numerical modeling tools. This proposal is in response to the need (b). Our primary objective is to apply a number of existing state-of-the-art modeling tools to predict the bed scour and morphological changes caused by LWD so that the tools may contribute to the design guidelines. Ultimately, we seek to have these tools operable with ease and in a desk-top computing environment. We realize that such numerical modeling tools are also critically needed for other research and projects at Reclamation. For example, there is a need to predict the bed scour and sediment gradation accurately for fish habitat assessment used by the aquatic production models being developed by Michael Newsom at the PN region. Such modeling tools are also needed to predict scour and morphological changes caused by in-stream structures such as rock weirs. The proposed effort will involve multiple regions and participation of both internal and external engineers and scientists. Specific benefits, once the entire proposed project is complete, include the following:

1. Availability of the advanced modeling tools used as part of a design process for LWD, as well as other in-stream structures, for risk and morphological change assessment.
2. Availability of the tools that make the representation of LWD and other structures automated. 3D representation of complex structures such as LWD has been very difficult and it has prevented most engineers from using 3D tools in the past. The CART3D approach will make the modeling tools easily accessible to most engineers on a desk top computer.
3. Contribution to the development of the LWD design guidelines.
4. Manuals that teach engineers on how to use these modeling tools.

Contributing Partners

Contact the Principal Investigator for information about partners.

Research Products

Bureau of Reclamation Review

The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.

Quantitative Modeling Tools of Scour and Morphological Impact due to Large Wood Debris Structures (final, PDF, 12.9MB)
By Yong Lai
Publication completed on September 30, 2016

This report documents the research and development carried out to address various priority issues facing the Large Wood (LW) installation at Reclamation river restoration projects. In particular, it focuses on determining the feasibility of using suitable computational modeling tools for LW installation as well as the development of relevant modeling tools at Reclamation. After a screening study of evaluating a number of open-source modeling tools that may be suitable to this project and a literature survey, a three-dimensional (3D) semi-automated mesh generator is revised and updated based on OpenFOAM's snappyHexMesh. In addition, an independent stand-alone semi-automated mesh generator is also developed. Then, the project focused on the extension and update of a 3D Reynolds-Averaged Navier-Stokes model U2RANS. A combination of 3D mesh generator and U2RANS allow engineers to simulate complex flows around LW structures in a riverine environment. A number of demonstration cases and project applications are used to test and verify the developed modeling tools. Results are compared with field measured data when available. It is shown that the developed 3D modeling tools can be used by engineers to predict flows around complex in-stream structures on desktop PCs.

Complex Flows Through Large Woody Structures (final, PDF, 522KB)
By Yong Lai
Publication completed on March 01, 2017

This bulletin summarizes the research results and potential application to Reclamation's mission.


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Last Updated: 4/4/17