Name of case study
Belle Island Brush Mattressing
Location
Johnson Creek, Belle Island, Portland, Oregon, USA.
Year
1993
Scale
building/single site scale.
Area / size
on a 125m stretch of Johnson Creek
NbS employed
Brush mattress
Type of NbS
Ecosystem not defined or specified
Initiator
The Oregon Department of Transportation (ODOT)
Funder
The Oregon Department of Transportation (ODOT)
Budget
unknown
Design group
Robbin B. Sotir & Associates, Inc. (RBSA)
- changes in rainfall
- coastal erosion
- coastal inundation and storm surge
- Desertification
- Flooding
- reduced soil quality
- soil erosion and landslides
- urban heat island effect
- Wind / storm damage
The Johnson Creek brush mattressing is an example of how nature-based solutions can be implemented to stabilise a streambank, and genuinely contribute positively to the landscape. Brush mattressing can be used in conjunction with a range of other nature-based solutions – here the team also implemented stone walls, using locally sourced stone, and mechanically stabilised earth.
- disaster risk reduction and resilience
The Johnson Creek project proved to be a successful solution to flood-induced erosion. Not long after it was constructed, and before the planting became established, the site flooded and the system protected the bank (Sotir, 1998).
The brush mattressing system becomes more resilient as time passes, because as the plants grow, the roots become established and interconnected, and a natural reinforcement occurs. This creates growing and strengthening disaster resilience over time.
- Habitat provision
- Species maintenance
- Habitat provision
- Species maintenance
As time has passed, the actual structure has faded almost completely into the landscape. The photos of the creek ten years after the project was built show a bank that is covered in vegetation, growing naturally. Such a system allows for habitat provision and species maintenance.
The living structure of a brush mattress also improves fish habitat by shading the stream, lowering water temperatures and offering protection from predators. It can also be a supporting habitat for birds, insects and other living organisms.
Summary of case study
The Johnson Creek in Milwauke, Oregon i the United States of America drains a highly urban area. When the creek was realigned to widen a bridge and complete the construction of a new motorway, it was shortened by around 20%. This work increased the gradient of the stream and increased risk of erosion and soil instability.
In 1993, work began to install a system to protect the outer bank, increase soil stability, and preserve the water quality and fish habitat. The initial plan was to use only riprap, which is an US American term referring to a permanent layer of stones as a stablisation intervention.
Soil bioengineering firm Robbin B Sotir & Associates put forward the alternate solution. A combination of vegetated and mechanically stabilised earth and some rock ripraps were installed. The upper bank was protected with a brush mattress system (Sotir, 1998).
Since installation, the vegetation has grown into the landscape, securing it further. The brush mattress has grown into riparian bush, which looks as if it has always been there.
Although this case study is located outside of Te Moananui Oceania, it is valuable to see how successful this method could be in streams and creeks. The method can be adjusted for Te Moananui Oceania climates, and to use native vegetation. As we continue to face issues of erosion, storm surge and flooding, a nature-based solution like brush mattressing can provide a solution that is not only effective but proven to positively contribute to the surrounding landscape, as seen in Johnson Creek.
References
- Sotir, R.B. 1998. Retrofit opportunities for Urban Waters Using Soil Bioengineering. Wetlands Engineering & River Restoration Conference Denver, CO. https://www.sotir.com/publications/retrofit.html