Author(s): Nicolas Francisco Gamarra; Roser Casas-Mulet; Nils Ruther

Linked Author(s): Roser Casas-Mulet, Nils Rüther

Keywords: Environmental flow; Thermal monitoring; Thermal Infrared (TIR) imagery; River-groundwater interaction; Hydrodynamic modelling; Thermal modelling; OpenTELEMAC

Abstract: Water temperature is widely recognized as a key driver of riverine ecosystem health, yet thermal stress resulting from anthropogenic alterations and climate change increasingly affects habitat quality and aquatic biota. Despite its ecological importance, t emperature is still not adequately integrated into most river management applications. Understanding, monitoring, and modeling river temperature are therefore essential for designing effective adaptation strategies and supporting climate-resilient management. This study combines multi-scale thermal monitoring with two-dimensional hydro-thermal modeling to analyse seasonal thermal patterns in a regulated, groundwater-influenced environmental flow stretch of the Lech River (Germany). Distributed temperature loggers and UAV-based thermal infrared (TIR) imagery were used to characterize spatial and temporal thermal variability. Results revealed pronounced heterogeneity, with groundwater-influenced backwaters emerging as the most thermally distinct zones. A TELEMAC - 2D/WAQTEL hydrothermal model integrating groundwater inputs reproduced the 2D flow field and the main temporal and spatial temperature dynamics of the site with good accuracy. Agreement was strongest in the well-mixed main channel, while higher uncertainty persisted in groundwater -influenced backwaters. Overall, the combined monitoring-modeling approach provides valuable tools for river management, enabling evaluation of adaptation strategies, such as increased environmental flows or reconnecting tributaries, aimed at improving hydraulic and thermal habitat quality under future climatic conditions.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.265

Year: 2026