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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #405244
Research Project: Science and Technologies for Improving Soil and Water Resources in Agricultural Watersheds

Location: Watershed Physical Processes Research

Title: Collapse of the San Rafael waterfall, Rio Coca, Ecuador and resulting catastrophic geohazard

Author
item Langendoen, Eddy
item Ursic, Michael - Mick
item Locke, Martin
item GIBSON, STANFORD - Us Army Corp Of Engineers (USACE)
item ESPINOZA-GIRON, PABLO - Electric Corp Of Ecuador
item BARRERA-CRESPO, PEDRO - Electric Corp Of Ecuador

Submitted to: International Symposium on River Sedimentation
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/2023
Publication Date: 9/5/2023
Citation: Langendoen, E.J., Ursic, M.E., Locke, M.A., Gibson, S., Espinoza-Giron, P., Barrera-Crespo, P. 2023. Collapse of the San Rafael waterfall, Rio Coca, Ecuador and resulting catastrophic geohazard. International Symposium on River Sedimentation. In Abstract Book of 15th ISRS Symposium, Florence, Italy, September 5-8, 2023.

Interpretive Summary: ABSTRACT ONLY

Technical Abstract: The February 2020 collapse of the 150 m tall San Rafael waterfall on the Rio Coca, Ecuador, resulted in rapid regressive erosion of the Rio Coca. The waterfall was located 19 km downstream of the Coca Coda Sinclair Dam (CCSD), which provides about 35% of Ecuador’s power demand. Since, the waterfall collapse the erosion front has migrated within 7 km of the CCSD, with channel incision ranging from about 100 m at the former waterfall location to about 20 m near the erosion front and up to 250 m of bank retreat. This has resulted in catastrophic losses of near-channel infrastructure (e.g., Panamerican Highway, pipelines transporting oil and gas from the Amazon to the Pacific) and loss in socioeconomic services to Amazonian communities. By request of the Government of Ecuador, the US Department of State and Department of Defense (US Army Corps of Engineers; USACE) have formed a US Government Interagency Expert Elicitation Team to assist the Government of Ecuador in hazard assessment and mitigation planning. In February 2023, the US Department of Agriculture conducted extensive jet erosion testing to quantify the erodibility of the three most common geologic units making up the bed material: Avalanche, Breccia, and Lacustrine. The measured critical shear stresses varied as follows: Avalanche material, 4.5-58.6 Pa; Breccia material, 8.5-22.0 Pa (gray colored) and 124-705 Pa (red colored); and Lacustrine material, 17.6-289 Pa. This information will support analyses to determine when the erosion front will reach the CCSD and the magnitude of incision, which is a critical need to select the best measures to prevent failure of the CCSD. In addition, experts from USACE, US Bureau of Reclamation, and US Geological Survey evaluated the possible downstream impacts of the eroded materials. The front of the bed load pulse has migrated about 20 km downstream of the former waterfall location, though the center of mass of the pulse is still within 5 km downstream of the former waterfall location. This bed load pulse will eventually block the outlet of the Coca Coda Sinclair hydroproject’s power plant (45 km downstream of the former waterfall location). The coarser grains (sand and small gravel) in the wash load will likely transition to bed material about 50 km downstream of the waterfall location, and therefore increase flood risk for the communities along the lower reach of the Rio Coca.