3 minute read
Matarandiba Island
Matarandiba Island, Bahia, Brazil
Using a nature-based solution for ensuring safe working conditions. The small island of Matarandiba lies just off the coast of Aratu, Brazil. Here in 2010, Dow cut back an existing hillside to provide access for operations personnel, but unfortunately significant rains and natural erosion resulted in obstructions and unstable and unsafe working conditions for construction contractors at the site. So in 2017, Dow considered three project plans to stabilize the hillside. The first option included blasting and heavy earthmoving equipment to completely remove the slope. The second, and most conventional option, was to drill and install mechanical anchors in the aggregate substrate to serve as tie backs for a steel-reinforced, sloped concrete overlay. The third, and least invasive option, involved constructing a gabion wall at the toe of the slope in conjunction with reestablishing a native vegetative cover to stabilize the upper portion of the slope. Of the three, Dow selected the third option because it minimized environmental impact and cost while maximizing restorative features.
Article cover: Aerial view of hillside in 2020. (Photo by Dow)
Producing Efficiencies
Dow’s engineering consultants undertook geotechnical field studies and slope stability analyses to design the combined gabion wall and vegetative cover. They needed to address the challenge of optimizing the existing hill slope and determining the suitability of existing materials for establishing vegetation. To ensure uptake of vegetation, the project team adjusted the pH of surficial soils and added a layer of natural organic material with cellulose along the exposed face of the hillside. Finally, the team installed a geosynthetic mesh to reinforce the vegetative surface cover.
Using Natural Processes
Gravity serves as the main mechanism for stabilizing the base of the slope while the reinforcement of native vegetative root system stabilizes the upper half of the slope. When compared to removing the hillside entirely to alleviate the erosion and hazardous working conditions, allowing vegetation to stabilize the slope restored more native habitat and naturally reduces the amount of rainwater runoff.
Broadening Benefits
The gabion wall and vegetative cover solution reduced the need for major earthworks, lowering the carbon emissions for the project by 90% and the cost of the project by $1 million. Overall, this solution had the least impact on the local ecosystem. By installing the gabion wall and vegetative cover, the project team reduced the project’s footprint from a potential 4 hectares for complete hillside removal to only 0.2 hectares. The result is a restored and stabilized hillside that serves as a nature-based transition to the native forest beyond.
Promoting Collaboration
By demonstrating the efficacy of a nature-based solution for the hillside erosion problem on Matarandiba Island, Dow’s project team provided the Brazilian government with a successful case study for environmental restoration and remediation. And because the team demonstrated to the Brazilian government the clear economic and ecological benefits of the gabion wall and vegetative cover solution, the approval and permitting process proceeded much more smoothly than had the team used a more traditional mitigation method.
