Concepto, análisis histórico y determinación de excedentes de la cuenca del Tajoaplicación al trasvase Tajo-Segura

Abstract

The Tagus-Segura Water Transfer (ATS) allows allocating water from the upper Tagus basin to the Segura basin. This water transfer infrastructure it is managed under to two fundamental principles: the Tagus basin is a priority basin (main unit management principle, Water Framework Directive ─WFD─ art 15) and it can only be transferred what it is considered and defined as “water surplus”. Since it was launched in 1979, the ATS has been operating below expectations, which generates contrary social-economic-political reactions. Because of these reactions, these unquestioned principles are not being applied. This Doctoral Thesis performs an analysis of the surplus character of the Tagus basin waters. The analysis of the current situation detects deficiencies in its management, so this Thesis therefor proposes a methodology to correct them with real results, applicable to the ATS management. The analysis shows that the current legal definition of water surplus is faulty. The source basin, the Tagus basin, is not adequately accounted. Moreover, the legal definition of water surplus does not explicitly determine how much water can be transferred. In order to fix this, Exploitation Rules were created with the theoretical objective of minimizing the hydrological exceptionality situations and by maintaining a uniform cadence of the transfers. These objectives are not fulfilled, as the exploitation results prove. Therefore, the problem is twofold: poor definition of water surplus, with consequences to the Tagus basin, and mismanagement of the ATS. This causes problems both in the Tagus basin and in the related uses of the water transferred. These problems can be analysed using the proposed methodology, suitably adapted to each circumstance. Moreover, this methodology allows obtaining suitable solutions. These solutions have two paths ways. First one, a mitigating measure: to revise the exploitation rules. In this case, management would improve, but not solving the problem of water surplus definition. Second one, a corrective measure, which will properly define water surpluses in the Tagus basin as the water that can be transferred. The application of the methodology technically gives clear and conclusive results. The proposal for new Exploitation Rules proves that it is possible to correct the irregularity of the water transfers and the contradictorily frequent situations of hydrological exceptionality. This scenario maintains the conditionality’s and limitations imposed on the Tagus of the current legal definition of water surpluses. In this case, legal water surpluses are still not real water surpluses. Also, this method allows estimating the real water surplus, considering no water limitations for the Tagus basin in order to achieve WFD environmental objectives. The estimate amount of water surplus is significantly low. This means that the current management of the ATS is incompatible with the WFD. It is a tough outcome that undoubtedly has its impact on the Segura basin. A very important problem, which must be appropriately, treated under the suitable administrative arrangements. But in no way should it impose additional pressure on the Tagus basin, nor should burden its management or the achievement of its objectives. This study refers to a case, but it can be extended to other large transfers. Either in conception or exploitation phase