Jacareí river plain after the 2011 mass movements: considerations from the granulometric analysis and channel planform changes

Abstract

The coastal plain of Paraná was formed by different continental and marine processes. Mass movements are examples of these processes. An extreme example of this process was observed in March 2011 in the Serra do Mar, where a sequence of landslides, mud and debris flows and floods with high sedimentary load reached the Jacareí River basin (central portion of the Paraná coast). In this paper, we analyze the granulometry of the sedimentary deposition left by the event from an open trench on the banks of the Jacareí river, as well as to investigate the changes that occurred in the river channel in the lowland portion, based on the years 2011, 2012 and 2019. The granulometry analysis was performed using pipetting and mechanical sieving techniques, while the channel analysis was performed in a geographic information system environment, based on orbital images and images collected by remotely piloted aircraft. The river was completely silted up in the most upstream and middle stretches of the plain in 2011, with the channel reopened later. In 2019, the Jacareí River presented in a stretch a return to the sinuosity patterns. The depositional layer left by the event was 50 cm thick and is composed predominantly of thicker material (very thick sand, granules and pebbles). Deposition environments were identified in the sedimentary layers below the layer left by the event. Recommendations for further analysis of the river channel and deposits generated over the entire plain are presented.