Analysis of different hypotheses for modeling air-water exchange and temperature evolution in a tropical reservoir

This paper presents an analysis of air-water exchange in a Colombian tropical reservoir. A coupled thermal-3D hydrodynamic model using TELEMAC-3D and WAQTEL is implemented to evaluate the dynamics of thermal processes in the reservoir. A sensitivity analysis is carried out on various modeling parameters, such as turbulence models, temperature diffusion coefficients, and heat exchange at the free surface based on observations. In particular, three different approaches have been tested to study the impact of air-water exchanges at the free surface: a constant water temperature, constant meteorological forcing, and time-varying meteorological forcing. All the simulations correctly represent the constant heating at the free surface for the first meters. However, no simulation has been able to correctly reproduce the amplitude of temperature oscillations in the surface layers: only the simulations with time-varying meteorological forcing show temperature oscillations, but their amplitude is greatly overestimated. Eventually, the analysis shows that the most crucial parameters for a correct representation of the observed temperature behavior are the heat exchange coefficient and the wind. The different approaches tested all have limitations, but they can reproduce reservoir temperature trends at different depths with a maximum standard deviation ranging from 3 to 8 degrees C.