Evolution of groundwater intensive development in the coastal aquifer of Telde (Gran Canaria, Canarian archipelago, Spain)

Abstract

A 75 km2, intensively developed coastal aquifer in eastern Gran Canaria island, Canarian Archipelago, around the town of Telde, has been surveyed and studied, using data from existing wells. The aquifer consists of Pliocene to Recent volcanic materials, with an intercalated detrital formation called Las Palmas Detritic formation (LPDF). Groundwater development in the area started late in the l9 th century by means of shaft wells fitted with horizontal water galleries and later on with horizontal drainage boreholes. Groundwater development became intensive since the 1950s. mostly for cash crop irrigation and town supply. First surveys are of the l970s. Groundwater development conditions follow a quickly changing pattern. There is a conspicuous water table drawdown, up to 40m in 20 years, following a strip parallel to the coast, although inland water table elevation is little affected. There is also a progressive water salinity increase with changes of the hydrochemical water type. Recent basalts were a good aquifer some decades ago but now are mostly drained. In spite of being considered the area as highly overexploited, groundwater reserve depletion contributes only about 5% of abstracted water, and more than 60% is transferred from inland areas. Discharge to the sea seems to be still significant, perhaps about 30% of total recharge.