Author(s): Rodrigo Junes; Sebastian Solari; Monica Fossati

Linked Author(s): ssolari, Mónica Fossati

Keywords: Hydrodynamics; Flow reversal; Uruguay river; TELEMAC-2D

Abstract: The last 350 km of the Uruguay river, from Salto Grande dam to the Río de la Plata estuary, are part of a natural border between Uruguay and Argentina, in South America, having around 600,000 inhabitants on its margins, and several commercial ports and marinas, which move around 3 to 4 million tons of cargo a year. This stretch of the river is a shared resource, being of great importance from a social, environmental and economical standpoint. Astronomical tidal waves and storm surges entering from the Río de la Plata estuary and propagating upstream are generally known to cause flow reversals on the Uruguay river, but up to date these have been seldom studied either via numerical modelling or field measurements. Their total distance of propagation, frequency and conditions of occurrence, duration in time, and velocity of flow reversal, are parameters relevant to the management of the river. This study aims to characterize the flow reversal events. In this context, a two dimensional hydrodynamic numerical model was implemented from Salto Grande hydroelectric dam to the Río de la Plata estuary, using TELEMAC-2D. The model was calibrated and validated using free surface elevation data from several stations along the river, as well as velocity data from ADCP measurement campaigns, resulting in the most detailed and exhaustively validated model of the lower stretch of the Uruguay river available to date. The model was used to generate a hindcast of velocity and free surface levels for the period 2004 to 2010. Velocity time series were extracted along the river’s main channel and processed using a series of filters and a watershed algorithms in order to identify individual flow reversal events, thus generating a new database from which these events were statistically characterized. This characterization showed that duration ranged from 1 to 34 hours, with velocities up to 1,3 m/s, and penetrations reached up to 285 km, with a mean frequency of occurrence of 3 to 4 events per week. The relationship of this characteristics with Salto Grande’s discharge was analysed, determining that the most intense events occur during periods of low discharge (less than 2,000 m³/s) coupled with storm surges from Río de la Plata entering the Uruguay river mouth. Conversely, similar storm surges coupled with high discharge (larger than 10,000 m³/s) produce weaker flow reversals, with a fifth the penetration and less than half the duration.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022212

Year: 2022