Research and Development Office

Quantitative Modeling Tools of Scour and Morphological Impact due to Large Wood Debris and Other In-Stream Structures

Project ID: 5772
Principal Investigator: Yong Lai
Research Topic: Sediment Management and River Restoration
Funded Fiscal Years: 2013
Keywords: large wood dedbris; 3d modeling tools; scour; morphology

Research Question

In a recent 2012 Reclamation S&T and USACE sponsored workshop on large wood debris (LWD) in fluvial environments, a number of key research needs relevant to Reclamation were identified. The highest priority group included focusing on the risk, safety, and the resultant scour and morphological impact to streams due to placement of LWD in rivers. Despite the existence of scour estimation methods such as bridge piers, methods or guidelines do not exist for predicting responses from construction of LWD. Even with traditional scour methods, they mostly rely on flume data that suffers from scale problems and field data that are scarce and expensive to get. In recent years, however, accurate scour and morphological predictions are becoming feasible with the availability of the state-of-the-art numerical modeling tools. These tools have not been evaluated and tested at Reclamation for LWD, but they were identified at the workshop to have potential to become the primary quantitative prediction tools for LWD related scour and morphological impact. We envision the proposed effort will involve multiple regions and participation of both internal and external engineers and scientists. Therefore, we propose a scoping study the first year with the objective of determining the feasibility of using suitable modeling tools and seeking potential collaborators. Specifically, the proposed study will answer the following questions:
1. Do modeling tools exist to predict bed scour and morphological changes caused by LWD and in-stream structures?
2. Are these modeling tools adequate for assisting LWD design related to risks associated with scour and morphological changes?
3. Can a strategy be defined for using models of different resolution for different project questions?

Need and Benefit

Large Wood Debris (LWD) has been widely used at several Reclamation regions for river restoration. Its use has been challenged due to a lack of general design guidelines that address the risk, safety, and morphological impact. A recent LWD workshop sponsored by S&T and USACE has identified the need to produce design guidelines and to use more advanced numerical modeling tools. This scoping proposal is in response to such a need. Our primary objective is to test a number of existing state-of-the-art modeling tools for their suitability to predict the bed scour and morphological changes caused by LWD so that the tools may contribute to the design guidelines. Further, such modeling tools, once verified, will also be applicable for a wide range of uses to other Reclamation projects. For example, model output would provide bed scour and gradation needed by the aquatic production modules for fish habitat study at the PN Columbia Tributary Program (contact: Michael Newsom), and provide design guidelines for other in-stream structures such as rock weirs for river restoration.
Specific benefits, once the entire proposed project is complete, include the following:
1. Availability of the advanced modeling tools 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 automated approach will make the modeling tools easily accessible to most engineers on a desk top computer.
3. 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 and Other In-Stream Structures (final, PDF, 992KB)
By Yong Lai
Report completed on May 09, 2014

Modeling How Large Woody Debris Structures Affect Rivers (final, PDF, 982KB)
By Yong Lai
Publication completed on September 30, 2014

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