Validation of a design equation for bendway weirs to control bank erosion and enhance river environment

Project ID: 2645
Principal Investigator: Chi Bui
Research Topic: Sediment Management and River Restoration
Funded Fiscal Years: 2016
Keywords: None

Research Question

Transverse features have been used at about 11 projects on the Middle Rio Grande (MRG) consisting of mostly
bendway weirs. Currently, state-of-the-art guidelines for bendway weir design focus upon ranges of geometric
parameters and do not provide information regarding hydraulic effects due to design parameter alteration. A
mathematical framework (Scurlock et. al., 2014) for the description of transverse in-stream structure induced
hydraulics as a function of geometric parameters was developed by Colorado State University (CSU) and funded by
the Albuquerque Area Office (AAO) of the Bureau of Reclamation. This mathematical framework was developed
from a large physical modeling database to predict changes in flow velocities along the centerline, inner-bank,
and outer-bank of a channel bend for different types of transverse structures. Two of the 11 recent bank
stabilization projects on the MRG applied the velocity reduction approach developed by CSU in the design of
bendway weirs. There have been limited field data to quantitatively support the hydraulics responses predicted by
the mathematical framework developed by CSU. The ecological benefits of bendway weirs have been studied but
not formally tested, especially regarding their benefits to fish species. They are thought to possibly allow for
physical habitat creation for certain life-stages of native fishes (Kinzli and Myrick, 2009), and with potential to
create conditions that promote riparian habitat revegetation.
The research focus will investigate hydraulic responses and their geomorphic and biological implications. The
research questions are separated into three disciplines, hydraulics, geomorphology, and biology. Specifically:
1/ How is field velocity data compared to the results predicted by the mathematical framework?
2/ What are long-term geomorphic responses as the result of installation of bendway weirs?
3/ Do bendway weirs promote the formation of lotic habitat that support native fish

Need and Benefit

New methods of bank stabilization such as bendway weirs are being used in lieu of traditional riprap revetments
for their cost saving and habitat benefits. In addition to bank protection, numerous applications of these
structures exist. For instance, bendway weirs and spur dikes are also used for reducing sediment deposits in front
of fish screens, intake structures and bypass structures. These types of structures are also used in river
restoration actions because they create variable velocity and depth flow conditions including eddies and shear
zones of flow separation.
The study proposed for the 2017 full scope S&T program will address a potential benefit for several regions in
Reclamation. The Lower Colorado River in the Lower Colorado region has a primary need to provide bank
stabilization using structures that provide fish habitat. The Sacramento River in the Mid-Pacific region has a need
for structures that reduce sediment deposition at recently constructed fish screen structures. The Columbia River
basin in the Pacific Northwest Region has a need for structures that provide improved habitat and bank stability
using natural materials. The Rio Grande Basin in the Upper Colorado region has needs for structures that provide
habitat restoration and bank stability that also improve habitat.
The ecological benefits of bendway weirs have been studied but not formally tested, especially regarding their
benefits to fish species. They are thought to possibly allow for physical habitat creation for certain life-stages of
native fishes (Kinzli and Myrick, 2009), and with potential to create conditions that promote riparian habitat
revegetation. The findings of the research will potentially benefit the Rio Grande Basin in the Upper Colorado
region where bendway weirs were recently installed as a method for bank stabilization at many projects.

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.

Validation of a design equation for bendway weirs to control bank erosion and enhance river environment (final, PDF, 3.1MB)
By Chi Bui
Publication completed on September 30, 2016

The as-built data collection occurred four months after the completion of construction of the bendway weirs. The 2015 as-built data showed that there had been geomorphic responses induced by the installations of the bendway weirs. The thalweg profile along the downstream weirs was relocated along the tips of the bendway weirs and a depositional trend has occurred along the toe of the right bankline.


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Last Updated: 4/4/17