Reconnaissance and Partnership of The Rio Coca Regressive Erosion Project

The Río Coca regressive erosion is an unprecedented event in non-geologic time scales. On February 2, 2020 the San Rafael waterfall on the Coca River in northern Ecuador collapsed. The catastrophic failure of the lava dam released over 200 million cubic meters of volcanic sediment downstream. Soon after the waterfall collapse, numerous oil pipelines, bridges, and structures failed as the regressive erosion propagated upstream in the valley. As of September 2022, the headcut has advanced approximately 11.1 km upstream and is only 7.9 km downstream from the intake structure associated with the Coca Codo Sinclair (CCS) hydropower complex – the largest hydropower facility in Ecuador. Following these events, the Government of Ecuador (GoE) through the Ministry of Energy and Non-Renewable Natural Resources and the Electrical Corporation of Ecuador (CELEC) began a dialog with the US Embassy and US Army Corps of Engineers (USACE) to develop a partnership with USACE. The purpose of the partnership is to provide technical assistance for the continual operations of the Coca Codo Sinclair hydropower complex within the context of the regressive erosion and progressive deposition.

USACE subject matter experts visited the Rio Coca through a WRDA 234 request and met with CELEC, Petroecuador, and the Ministry of Energy and Non-Renewable Natural Resources during a trip in July 2021. During the reconnaissance visit, several key observations were made that shaped the international partnership. The failure of the San Rafael lava dam and the processes that event initiated are unique globally, especially considering the potential impacts to infrastructure (hydropower production at the Coca Codo Sinclair hydropower complex). The team identified two potential modes of failure that could impact the CCS operations in the coming seasons: 1) Regressive Erosion (acute problem); and 2) Continual Progressive Deposition at the discharge tunnel (chronic problem). Based on these findings it was recommend to develop a team dedicated to understanding and developing measures for the regional progressive deposition trend at the discharge tunnel in addition to the team dedicated to the regressive erosion. USACE provided responses to charge questions associated with viable measures for arresting the regressive erosion, physical modeling recommendations, construction sequencing, and risk management.

Following the reconnaissance mission, a report of observations, findings, and considerations from the July visit was developed by the USACE team. In addition to the technical deliverable, the USACE project management team began discussions with CELEC on building an international partnership through the mechanism of a Foreign Military Sales (FMS) case, which was signed in December 2021. The primary tasks associated with the case included: 1) Physical Modeling of Proposed Regressive Erosion Solutions; 2) Collaborative Analysis and Engineering Support to the regressive erosion and progressive deposition issues; 3) Technical Visits to the United States; and 4) Expert Elicitation.