Analysis of Stable Isotopes of Runoff Sources and their Implication in Hydropower Projects, Cases of Study of Manduriacu and Coca River Basins in Northern Ecuador

Understanding the contributions of water sources to hydropower is crucial for characterizing hydrological processes in watersheds with limited data and resources. Specifically, these processes in Ecuador are more complex, and long-term monitoring is limited; hence, estimating runoff sources is challenging. In order to unde0.rstand these processes, the stable isotopes of δ ¹⁸ O and δD were analyzed from monthly runoff samples from various tributaries draining the northern Andean watersheds, encompassing elevations from 500 to 5,897 meters, which contribute to hydropower generation for both projects. The sampling period was from August 2017 to September 2018. The comparative analysis of the watersheds with different headwater sources helps to characterize the runoff, with tributaries contributing to both hydropower projects originating from glaciers and the Andean Paramo system. The Malo and Mashpi Rivers, located in the Amazon and Pacific drainage basins, respectively, do not receive high-elevation water; instead, they represent local water sources. These two rivers join downstream projects and were included in the sampling process for comparative purposes, despite not influencing hydropower generation. The significant role of altitude in influencing the stable isotope composition of rainfall-runoff waters in both hydropower projects indicates that Manduriacu predominantly receives runoff from high-elevation water sources in the paramo systems. Lower elevation rainfall-runoff processes govern the Coca-Codo Sinclair Hydropower intake project on the eastern side. From a hydropower management perspective, this research found that 95% of the total energy produced in these systems came from local downstream Amazon rainforest rainfall runoff during the sampling period.