Fluvial Geomorphology and Process of Regressive Erosion of the Coca River in the Amazon Foothills of Ecuador.
Abstract
The hydrographic basin of the Coca River is located in northeast Ecuador, covers an area of around 5000 km2 in the Amazon foothills, and is affected by tectonic and volcanic activity. One of the main traits of this river is the San Rafael waterfall, the highest in the country with a height of around 150 m. The waterfall collapsed in February 2020, initiating a process of regressive erosion that has increased along the path of the river constantly. The resultant slope failures, due to the adjustment of the valley to river deepening has caused the collapse of one of the main pipelines that carries oil from the main oil fields (Amazon basin) to the coast, and of highway E35, one of the main north-south roads. Additionally, the largest hydroelectric plant in Ecuador, the Coca-Codo Sinclair dam, is located upstream of the waterfall collapse in the path of the regressive erosion. These impacts have directly affected around 25000 people. The estimated economic losses are 4 million dollars/day, and if the Coca-Codo Sinclair dam is affected, this would represent a loss of 1.6 billion dollars (1.62% of Ecuador's GDP).
In the present project, we combine interpretation of aerial imagery, geologic maps and fluvial morphometric analyses to study the incision of the Coca River caused by the regressive erosion. The imagery analysis helps to establish the location of the knickpoints through time as well as changes in the sinuosity of the river. We also use Digital Elevation Models of varying resolutions to constrain the χ values of the Coca River and its tributaries in order to better understand the state of equilibrium, or not, of the river, and what this can tell us about the possible future arrest of incision. Our results show that when the Coca River crossed lava flows from nearby Reventador volcano, this lead to the creation of a section of the river with an abnormally low normalized steepness (kn). When the waterfall collapsed, the river started adjusting rapidly via an upstream migrating knickpoint due to the low resistance to erosion of the underlying alluvial deposits. This knickpoint migration is the result of the river returning to the previous steady state it had attained prior to its damming. We also present calculated rates of knickpoint migration, its relation to the seasonal precipitation and estimates of when it will reach the Coca-Codo Sinclair Dam.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.H53C..05L