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Photo: Ministerio de Defensa del Perú/Flickr
The rains in northern Peru have been 10 times stronger than usual this year, leading to floods, landslides and a declaration of a state of emergency in 10 regions in the country. Together with the human and economic toll, these downpours have inflicted tremendous damage to transport infrastructure with added and serious consequences on people’s lives.
These heavy rains are blamed on El Niño, a natural phenomenon characterized by an unusual warming of the sea surface temperature in the central and eastern equatorial Pacific Ocean. This phenomenon occurs every two to seven years, and lasts about 18 months at a time. El Niño significantly disrupts precipitation and wind patterns, giving rise to extreme weather events around the planet.
In Peru, this translates into rising temperatures along the north coast and intense rainfall, typically shortly before Christmas. That’s also when “huaicos” appear. “Huaico,” a word that comes from the Quechua language (wayq’u), refers to the enormous masses of mud and rocks carried by torrential rains from the Andes into rivers, causing them to overflow. These mudslides result from a combination of several natural factors including heavy rains, steep slopes, scarce vegetation, to name a few. But human factors also come into play and exacerbate their impact. That includes, in particular, the construction of human settlements in flood-prone basins or the absence of a comprehensive approach to disaster risk management.
This year’s floods are said to be comparable to those caused by El Niño in 1997-1998, one of the largest natural disasters in recent history, which claimed the lives of 374 people and caused US$1.2 billion worth of damages (data provided by the Peruvian National Institute of Civil Defense).
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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.
