Thermo-hydrochemical modelling of vertical profiles of the formed Meirama Lake (NW Spain)

The use of modelling techniques for the study and thermohydrochemical characterisation of lakes is conditioned by the availability of data with which to validate the model created. There are not many validated numerical models that reproduce the physico-chemical behaviour of a lake. During the period March 2008–October 2019 we have been monitoring the filling and post-filling process of an old open-pit, forming the Meirama lake in NW Spain. With the data measured during these years we have had the opportunity to develop a model of the thermo-hydrochemical behaviour of the vertical profile of the lake. Thus, this article presents a vertical profile numerical model of the thermal behaviour and transport of sulfate of the lake under the current conditions of steady-state hydrodynamic operation, when the complete flooding of the mine pit was reached (May 2016–October 2019). The model developed has been a conservative diffusive transport model and a thermal conductive transport model. The developed model reproduces acceptably the vertical profiles of the analysed parameters. In these profiles, it can be seen that the chemocline originating from the filling process diffuses slowly. There are two differentiated water bodies separated by a chemocline. The model also reproduces the seasonal evolution of the temperature profile in the shallowest zone of the lake; i.e., there is a significant thermocline in the upper zone that tends to disappear during the winter season: it tends to homogenize at a temperature between 11 and 12 °C, tending to a vertical profile.