Modeling aquifer–river interactions under the influence of groundwater abstraction in the Mancha Oriental System (SE Spain)

The Mancha Oriental System (MOS, 7,260 km²) is one of the largest aquifers within Spain, and is encompassed by the Jucar River Basin. Over the past 30 years, socioeconomic development within the region has been largely due to intensive use of groundwater resources for irrigating crops (1,000 km²). Groundwater pumping (406 million m³/year) has provoked a steady drop in the groundwater level and a reduction of MOS discharge to the Jucar River. The study aims to characterize the river–aquifer relationship, to determine the influence that groundwater abstraction has on the river discharge. This research has advanced a three-dimensional large-scale numerical groundwater-flow model (MODFLOW 2000) in order to spatially and temporally evaluate, quantify and predict the river–aquifer interactions that are influenced by groundwater abstraction in MOS. It is demonstrated that although groundwater abstraction increased considerably from the early 1980s to 2000, the depletion of water stored in the aquifer was lower than might be expected. This is mainly due to aquifer recharge from the Jucar River, induced by groundwater abstraction. The area of disconnection between the river and the water table (i.e. where groundwater head is lower than the riverbed) is found to have spread 20 km downstream from its position before pumping started.