EVALUATION OF THE SUSTAINED YIELD OF GROUNDWATER RESOURCES IN THE AQUIFER OF THE DETRITAL TERTIARY OF MADRID

摘要

The aquifer of the detrital Tertiary extends over an area of 2650 km~2 within the District of Madrid (see Fig. 1) which is its most exploited part and contributes to the water supply of 4.5 million people.The aquifer consists of arkosic sands deposited as alluvial fans during the Neogene. Locally, it reaches a thickness of over 3000 m. The depth of the wells exploiting its water, however, does not exceed 500 m.In accordance with earlier investigation [1], the hydraulic conductivity in the horizontal direction was found to be in the range 0.5 to 1 m per day (6 × 10~(-6) m·s~(-1) to 1.2 × 10~(-5) m·s~(-1)) whereas in the vertical direction it was as much as a hundred times lower. The specific yields of the wells did not exceed 3 L·s~(-1)·m~(-1). The aquifer was considered to be unconfined, very anisotropic and periodically recharged by infiltration of precipitation in the watershed divide areas, and discharged at the valley bottoms. Geochemical and isotopic data [2, 3] are in evident agreement with this idea of groundwater flow.