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climate change adaptation

Preparing transport for an uncertain climate future: I don’t have a crystal ball, but I have a computer

Julie Rozenberg's picture
Photo: Alex Wynter/Flickr
In 2015, severe floods washed away a series of bridges in Mozambique’s Nampula province, leaving several small villages completely isolated. Breslau, a local engineer and one of our counterparts, knew that rebuilding those bridges would take months. Breslau took his motorbike and drove the length of the river to look for other roads, trails, or paths to help the villagers avoid months of isolation. He eventually found an old earth path that was quickly cleaned up and restored… After a few days, the villagers had an alternative to the destroyed bridge, reconnecting them to the rest of the network and the country.

What happened in the Nampula province perfectly illustrates how a single weather event can quickly paralyze transport connections, bringing communities and economies to a screeching halt. There are many more examples of this phenomenon, which affects both developing and developed countries. On March 30th, a section of the I-85 interstate collapsed in Atlanta, causing schools to close and forcing many people to work from home. In Peru, food prices increase in Lima when the carretera central is disrupted by landslides because agricultural products can’t be brought to market.

How can we help countries improve the resilience of their transport networks in a context of scarce resources and rising climate uncertainty?

The “plastic bridge”: a low-cost, high-impact solution to address climate risk

Oliver Whalley's picture
Also available in: Français
Photo: Anthony Doudt/Flickr
Bridges are critical links in the transport network. In their position across waterways, they are exposed to the full effects of flooding and landslides, and are often the first pieces of infrastructure to be damaged in the event of a disaster. They also typically take weeks or months to repair.  Besides causing expensive damage to the infrastructure itself, disruptions in connectivity also have a much broader impact on economic productivity and people’s ability to access essential services. As many places are expected to witness more intense and frequent rainfall as a result of climate change, the risk to bridges will only worsen: more rainfall will lead to bigger river flows and more damage to bridges, especially those designed to handle smaller storms.

At each end of a bridges is a structure which supports the weight of the deck. These are known as abutments, and they are often the first part of the bridge to fail. Blockage of the main channel by debris can cause water to look for the path of least resistance around the sides of the bridges, thus placing the abutments at risk.

Traditional bridge construction requires the installation of piles for the foundations of abutments—a lengthy and expensive process that involves specialist materials, skills and equipment.

But there is another promising solution: Geosynthetic Reinforced Soil (GRS) abutments. These allow for rapid and resilient construction of bridge abutments using locally available materials, without specialized equipment. With GRS, bridges can be constructed in as little as five days (Von Handorf, 2013) and at a cost 30-50% lower than traditional approaches (Tonkin and Taylor, 2016) .

GRS abutments are based on ‘geogrids,’ a high density mesh made out of polyethylene (plastic). Layers of soil and geogrid are combined to create a solid foundation for the bridge deck. Construction can be completed with basic earthmoving and compaction equipment, and a range of local fill materials can be used with guidance from geotechnical specialists.