United States Department of Transportation
i
Applying Engineered Logjams and Dolosse for Streambank Stabilization
-
2021-02-01
-
[PDF-11.60 MB]
Details:
-
Creators:
-
Corporate Creators:
-
Subject/TRT Terms:
-
Publication/ Report Number:
-
Resource Type:
-
Geographical Coverage:
-
Contracting Officer:
-
Corporate Publisher:
-
Abstract:Engineers at the Federal Highway Administration Western Federal Lands Highway Division are installing long-term streambank stabilization intended to preserve highway infrastructure as well as minimize environmental impacts. An emerging approach called "engineered logjams" (ELJs), which uses precast concrete dolosse (i.e., reinforced concrete blocks in a complex geometric shape), is being considered for use in the Upper Hoh River Road bank-stabilization project. ELJs mimic logjams found in nature. Such logjams can redirect the channel flow and mitigate destructive erosive forces. As an additional benefit, the logs and debris can create or enhance fish habitat. A 1:25 scale model of a proposed ELJ design was tested in a flume for different flow conditions on movable bed and bank material. The physical modeling was complemented by computational fluid dynamic (CFD) modeling to investigate the stability of proposed ELJ installations during floods and to advance the design of ELJs for streambank stabilization. Several findings emerged from the cases evaluated in this research project: (1) ELJs proved to be effective in deflecting high-velocity approach flows away from the erodible streambank into the main channel; (2) results obtained from the ELJ model with loose bed and bank material showed that localized streambed scour around the structure does have an effect on its stability; (3) the effectiveness of structural modifications to the ELJs, such as the placement of key dolosse, addition of riprap, and partial burial of the ELJ was determined; and (4) a repeatable ELJ unit design can provide structural stability against high-velocity flows and streambed scour with an appropriate combination of wood and ballast meeting specific density and void ratio requirements. In addition, this study derived drag coefficients for this type of ELJ unit based on force measurements and CFD modeling. Future work is needed to evaluate the transferability of these findings to other ELJ types and configurations. This research study achieved the main goal of creating environmentally friendly streambank protection and local fish habitat. Findings from this research study will be of interest to river engineering designers who may build similar structures for streambank stabilization projects.
-
Format:
-
Funding:
-
Collection(s):
-
Main Document Checksum:
-
Download URL:
-
File Type:
