Storage Regimes Of The Yesa Reservoir, Upper Aragon River Basin, Central Spanish Pyrenees

Abstract

Agriculture in Mediterranean countries is mainly based upon the irrigation of productive areas in the lowlands. To achieve this, it is necessary to store large volumes of water in reservoirs located in mountain headwaters. These reservoirs have a relatively simple regime of storage, increasing the water stored along the wet season (from October until May) and reaching the maximum volume shortly before the beginning of the hot, very dry season, when the water is released. This paper considers the storage regime (inflow and outflow) of the Yesa Reservoir in the Spanish Pyrenees, as an example of management of a large reservoir in a mountain Mediterranean environment, subject to a strong interannual variability. On average, the highest water storage level is achieved by retaining the high flows of the Aragón River in autumn and spring. Nevertheless, the irregularity of rainfalls and the existence of changes in the hydrological regime lead to changes in the patterns or reservoir infilling. Three patterns were identified in the Yesa Reservoir: (1) a quick increase of the stored volume in autumn, a stabilisation in winter and a new increase in spring; (2) a lower stored volume in autumn, strong increase at the beginning of winter and a new increase in spring; and (3) a continuous increase from October until May. These patterns are distributed in time over different periods since the construction of the reservoir in 1959, demonstrating the adjustment of the reservoir management to changes in the hydrological regime