Author(s): Miluska Anthuannet Rosas Barturen; Luis Moya; Giannina Varillas-Salazar; Angela Peralta-Solorzano; Cristhian Asis

Linked Author(s): Miluska Anthuannet Rosas Barturen

Keywords: Channel narrowing; Erosion risk; Hydraulic modelling; Peru; Urban expansion

Abstract: Unplanned urban expansion along river corridors has exacerbated flood risk in many Latin American cities by increasingly restricting the natural discharge capacity of rivers. This study investigates the hydraulic and morphodynamic response of a narrowed urban section of the Rímac River (Peru), focusing on the area around the Carapongo pedestrian bridge. An exploratory analysis was conducted using historical satellite imagery (2004–2024) and discharge data from the Chosica gauging station to quantify changes in river geometry and hydraulic conditions. The results show a reduction in river width of approximately 40% over the last decade, accompanied by a 35% increase in flow depth under comparable discharge conditions. This indicates a significant loss of discharge capacity and an increased flood risk. In a second step, a twodimensional (2D) hydraulic model was developed using HEC-RAS 2D, supplemented by high-resolution topographic data derived from UAVs and sediment data from the field. The simulations show average flow depths of up to 2.0 m in the bridge area and downstream. This identifies critical, flood-prone zones influenced by the narrowing of the riverbed and the infrastructure. Local bed erosion of approximately 1.0 m upstream of the bridge and sediment deposition downstream indicate morphodynamic feedbacks that further exacerbate the flood risk. The results demonstrate that the narrowing of the riverbed caused by informal development significantly increases the flood risk. They underscore the importance of integrating current geodata into 2D modelling for risk-based management of urban rivers.

DOI: https://doi.org/10.64697/iahr.proc.hic2026.161

Year: 2026