Study of the secondary flow at the confluence of the Marañón and Ucayali rivers using a three-dimensional numerical model

The confluence of the Marañón and Ucayali rivers form the beginning of the Amazon River, considered the largest and longest river in the world, located in the north of South America, in Peru in the department of Loreto. These rivers generate complex mixing pro cesses, where secondary flows are observed that drive the mixing of sediments. The objective of this research was to study the secondary flow at the confluence of the Marañón and Ucayali rivers using a three-dimensional numerical model, which was calibrated and validated using information measured in the field. Two case studies related to field measurements were presented, where Case I represents measurements during the low water season and Case II represents meas urements during the high-water season. Five sections were presented for the calibration and val idation of the three-dimensional numerical model located near the confluence of the Marañón and Ucayali rivers. Of which two sections are in the Marañon and Ucayali rivers respectively, and the remaining three sections are in the confluence zone. The results of the three-dimensional numerical models in both cases replicated the hydrodynamics measured in the field. In turn, two secondary flows rotating in opposite directions were formed within the confluence zone, the for mation of these secondary flows were contrasted with the field measurements. Despite the large width to depth ratio within the confluence zone, large secondary flows were observed. Where the three-dimensional numerical model of Case II presented larger size of secondary flows compared to Case I. Finally, from the performance analysis it can be said that the Case I model presented a better fit with the data measured in the field, however both three-dimensional numerical models were able to replicate the hydrodynamics and secondary flows measured in the field.