Avulsion of the Magdalena River, Pinillos Sector, Colombia

Abstract

Fluvial dynamics or avulsion occur in plains, intramontane valleys, alluvial plains in low basins, river confluences, and fluvio-marine deltas, and are driven by factors such as sedimentation, hydroclimatic events, geology, geomorphology, and floods. In the Magdalena River, the main river of Colombia, a rapid morphological and hydrological change took place in its lower basin due to the closure of a section of one branch and the formation of a new channel. This altered the area’s hydrological and geomorphological configuration, contrasting with typical meandering dynamics. In this study, a multitemporal analysis (1985–2024) of satellite images was performed to assess the morphodynamic evolution of the Magdalena and Cauca Rivers. Additionally, natural factors such as geology, geomorphology, fluvial dynamics, and sediment concentration were evaluated for their role in the avulsion of the Magdalena River in the Pinillos area of Colombia. As a result, a thematic map was developed to systematically assess and monitor physical variables in fluvial avulsion studies. Contrary to the predicted scenario (the closure of the Pinillos meander), after the 2010– 2011 La Niña event the Magdalena River suddenly changed its course through a channel called Victoria, altering the geomorphological and hydrological configuration of that sector of the river. The resulting cartography shows evidence of sedimentation in the closed branch and the widening and connection of smaller channels that formed the new active bed of the Magdalena River.