Ecuador

San Rafael region, Amazonian provinces of Napo and Sucumbí

Regional

In February 2020, the riverbed collapsed above the Cascada de San Rafael, the Andean country’s tallest waterfall, which disappeared in minutes as the river changed course. A huge sinkhole appeared in the Coca River, a few meters before the falls, and diverted the watercourse. Following the abrupt riverbed collapse, the water changed course, starting falling in three separate sections and at a less steep slope. Since then, the riverbed is continuously shifting its course.

The precise cause of the landslides, however, remains a point of controversy.

The Ecuadoran government and several geologists insist the fast-creeping collapse of the riverbed is a natural phenomenon, despite the fact that other experts say the erosion process could have been accelerated due to the sediment retention at the Coca Codo Sinclair (CCS) dam.

- Regarding the natural phenomenon argument:
The river and falls of the San Rafael Waterfall cut through a thick patch of cloud forest at the intersection of the Andes Mountains and the Amazon Basin. The waterfall lays in a seismically active area that’s home to the Cayambe volcano and Reventador volcano. The falls were formed presumably tens of thousands of years ago by a volcanic dike extruded into the river valley by the adjacent Reventador volcano, one of the most active in the world, which last erupted on 11/03/2002. Given the area’s geology, landslides are naturally occurring. According to the "World Waterfall Database", there is an on-going transformation of the cliff forming the falls since mid 2008. Nonetheless, geologists are still unsure what caused the erosion in a natural area known for its unstable terrain, but the landslides are moving rapidly upstream.

- Regarding the Coca Codo Sinclair (CCS) dam argument:
Some experts argue that the landslides were actually the result of the recent construction of CCS Dam, one of Ecuador’s largest hydroelectric plants with a capacity of 1500 MW. The CCS dam was built in 2016 at approximately 20 kilometers upstream from the falls.
This argument is based on the fact that the dam requires river water to be filtered so it doesn’t damage the equipment. The lack of sediment causes the water flow to become more erosive to the bed and banks of the river below the dam, making it more prone to collapse.
According to an article published in "southernaffairs.org", the Coca-Codo Sinclair hydroelectric dam was also criticised for being plagued by accidents and design flaws, while two years after its inauguration, its turbines were clogged with silt and debris, and thousands of cracks had appeared in its structure.

10 - 100 M USD

Since February 2020 (riverbed collapse of the Cascada de San Rafael waterfall), the riverbed has continued to shift course. Studies commissioned by the Ecuadoran government call for emergency infrastructure to mitigate the "regressive erosion" phenomenon which:
- has progressed at an accelerated rate along the Coca River (i.e., roughly four kilometers of erosion in five months, 02/02/2020 - 06/07/2020) and along one of its tributaries, the Montana River;
- could affect other bodies of water, e.g., the Loco River, Marker River, Piedras Finas gorge, and Malo River;
- could represent flood risks for nearby communities, the Coca Codo Sinclair discharge tunnel and eventually the powerhouse due to
the accumulation of sediment downstream (between 40 million and 60 million cubic meters of sediment have been detached)

When the 150-meter (500-foot) San Rafael Waterfall disappeared, experts warned of the enormous risk this phenomenon posed, especially to:
- the oil pipelines that pass through the area, subject to due to scouring, exposure of the pipelines, and failure of their support;
- a national highway (i.e., bridge on the Baeza-Lago Agrio road; the road had to be closed as a precaution for more than a month);
- a nearby human settlement and indigenous communities;
- the catchment dam of the Coca Codo Sinclair hydroelectric plant that also face the threat of foundations undermining and scouring.

The Ecuadoran government signed an official declaration of emergency in this important area of ​​Cayambe Coca National Park (11/05/2020). Preventive measures are taken to reduce the disaster risk for the CCS catchment dam. It is estimated that the strategy to deal with the regressive erosion of the Coca River will cost $20 million or even higher.