Once upon a time, in Don Quixote's land... The story of Mancha Oriental Aquifer: Past, lessons learned and future scenarios

Abstract

The present study offers a retrospective look and sketches the future challenges in one of the most extensive and exploited carbonate hydrogeological aquifer systems in Europe - Mancha Oriental Aquifer (MOA). With considerable extent of 7,520 km2 MOA is completely encompassed within Júcar River Basin (JRB), a pilot site in the European Union. MOA represents a paradigmatic case study characterised by semiarid climate, growing anthropogenic pressures, and complex river–aquifer interactions. The hydrogeological potential of the area, the discovery of submersible pumps, the low cost of energy and the high price of crops such as corn during the last quarter of the twentieth century, intensified the construction of boreholes by individuals; transforming approximately 1000 km2 of traditionally rain-fed land into irrigated surface, leading to significant socioeconomic development in the region. In the first decade of 21st century, groundwater pumping in MOA (98% of which is used for irrigation) was no longer compatible with the estimated sustainable volume, which, together with drought periods, led to a significant decrease in the groundwater levels (as much as 80 m in some areas) and a reduction in the water inflow from MOA to Júcar River. The JRB Authority and the Mancha Oriental Users Community realized the unsustainability of the situation and set a number of actions to revert it (Sanz et al., 2018; Cassiraga et al., 2019) among which the following could be highlighted: regularizing water rights and control of extractions through the design of an exploitation plan with annual periodicity; improving the efficiency of irrigation systems; replacing (since 2001) groundwater pumping in several areas of MOA with surface water from outside the system; replacing (since 2003) groundwater supply to the city of Albacete with water from Júcar River; state financed water rights’ acquisition, paid to certain users during periods of intense drought.

Additionally, a groundwater flow model of MOA has been developed and is available for more than 10 years (Sanz 2018, Cassiraga 2019). It is updated periodically and serves as a management tool for decision making regarding the evolution of groundwater levels and the determination of water balances in the context of pumping replacement scenarios, climate change, etc.  Recently Jucar River flow model has also been developed in order to obtain more detailed scope at the hydrodynamic processes and their space-time distributions of 121 km river reach for 45 years period (1974–2019) on a daily scale (Dountcheva at al 2023).

As a result of the measures taken the MOA has been in a quasi-equilibrium state with a steady yearly balance in recent decades. This stabilization is currently in danger due to the proliferation of wells with irrigation rights of up to 7000 m3year-1, used to irrigate expanding crops like almond and pistachio trees. These wells are treated differently during the concession process and are not subject to the same controls as wells with larger extraction volumes. The MOA is in a state of quantitative overexploitation as a result of this fact and the 114 hm3 volume of environmental restrictions set by the most recent JRB water management plan (CHJ 2022). Future scenarios evaluation and adoption of new actions are completely necessary. Managers and users currently have a collaboration agreement with the Universities of Castilla-La Mancha and Politècnica de València (both belong to JRB district), aiming to maintain and further develop the MOA flow model (MODOS project). This operational model is updated annually and provides more detailed knowledge of MOA behaviour and the spatio-temporal distribution of its relations with Júcar River, as well as future scenarios evaluation, being a fundamental element in the management of MOA.