SURFACE AND GROUND WATER FLOW MODELLING IN THE RESTORATION OF THE MEIRAMA OPEN PIT MINE

The interaction between the free surface and the ground water flows in a basin is a fundamental issue in the study of several environmental problems that require a comprehensive knowledge of the balance and quality of the water flows. Nowadays there is a good number of numerical models in the market, that allow for an evaluation of the free surface hydrodynamics, in one side, and for the groundwater flow in the other side. Still, there is a lack of model skills to evaluate the free surface and ground hydrodynamics in a joint way, and moreover including water quality criteria. The Ingenieria del Agua y del Medio Ambiente (Water and Environmental Engineering Group) group has been working in these fields for some years and has developed a software that allows for the numerical evaluation of this kind of problems. In this work it is shown the application of the developed codes to the working out of a model that evaluates the joined surface and ground water flows in an opencast mine to be restored as a lake. The so-predicted results are presented as a conclusion to shortly elaborate other alternatives in order to restore the opencast mine as a lake. Meirama opencast mine The mining activities that have been taking place in the Meirama opencast lignite mine are to be abandoned at the end of 2007. The firm LIMEISA (LIgnitos de MEIrama Sociedad Anonima) has been exploiting Meirama mine since 1980. The lignite deposit is situated in the province of La Coruna, north-western Spain, 25 km from the city of La Coruna. A 550 Mw power station, fuelled by the lignites of Meirama, was built nearby to produce energy from Meirama coals. At the moment of its closure in 2007 the mine will have produced some 87 million tons of lignite. Mine tailings of some 160 million m 3 were moved to a nearby storage tip. The mine has been producing from 4 to 10 million m 3 per year during the first years of the exploitation and some 3 million m 3