15. Estimation of Groundwater Resources According to Watershed and Groundwater Divide

This paper estimates groundwater resources in four groundwater bodies shared between different planning areas, specifically the hydrographic basins of the Segura and Jucar rivers that transit entirely within the Spanish State and flow into the Mediterranean Sea. Three of these masses are overexploited, while the fourth has increased its resources thanks to the excess irrigation that is carried out mostly with surface water. This comes from a transfer that takes place between the Tagus and Segura rivers. Given that Spanish legislation considers that the recharge of an aquifer is assimilable to groundwater resource. These have been determined, both for the undisturbed state (without pumping) and for the disturbed (with pumping and irrigation returns) by means of the code RENATA. The calculations have been made not only from the perspective of the watershed divide, but also from the point of view of the groundwater divide. The results that have been obtained have revealed a remarkable and significant casuistry. In this regard, it should be noted, among the conclusions that have been drawn, that the concept of groundwater divide makes sense to use it only when aquifers discharge water into the surface hydrographic network or into the sea, since when aquifers are overexploited and springs and groundwater discharges to rivers have dried up, the notion of recharge as a renewable resource does not make any sense, since the recharge that takes place in the aquifer only contributes to alleviating or palliate the consumption that is being made of its reserves.