La gestión del agua en Riegos del Alto Aragón: de los grandes embalses a las pequeñas balsas

This Master Thesis is a study of different aspects of water resource management in the project of “Riegos del Alto Aragón”, the largest irrigation project in Spain and even Europe. The main objective is to analyze the basic functioning of irrigation infrastructures and their interactions, and the changes they have experienced as a result of the so-called modernization of irrigation. The study area is located between the Huesca and Zaragoza provinces in Aragon, Spain, with a semiarid climate where rainfed agriculture faces low productivity and a large uncertainty in the crops. So, since the mid nineteenth century there is a growing demand for the use of the discharge of the Pyrenean Rivers (Gállego and Cinca). Finally, the Riegos del Alto Aragón project was approved in 1915 although it has not yet finished actually. Since then, a complex infrastructure has been slowly developed, trying to supply water to 300.000 hectares according to the initial project, although much later revisions have lowered the expectations. In 2012 more than 120,000 irrigated hectares have been transformed, contributing very significantly to the increase in crop productivity and diversity, as well as the landscape and economic diversification affecting to a territory larger than the irrigated area. For this reason several dams have been built, with their smaller ditches, small internal reservoirs and, irrigation reservoirs with their pumping stations, a complex infrastructure network reflecting the purpose of transforming the space and the use of water in the most efficient way. The analysis of the management of water infrastructure (dams and canals), allows us to conclude that in wet years there are no restrictions on irrigation water demand, whereas in dry years, water scarcity at the beginning of the irrigation season (March) forces to establish a quota system limiting the number of cubic meters per hectare available for each farmer. This means that farmers have to adopt critical decisions when choosing crops and surfaces to be irrigated. Also, the study of the typology of the irrigated area in Riegos del Alto Aragón demonstrates the existence of two groups. (i) On one side, the ancient irrigation systems are the first that have been transformed in the 1950’s, 1960’s and 1970’s, dominated by small parcels sometimes bench-terraced, dominated by winter cereals and overflowing irrigation systems. (ii) On the other hand, there are modern or modernized irrigated areas that have been launched in the 1990’s and 2000’s. They are characterized by large parcels (due to land concentration), disappearance of terraces, with a predominance of pressurized irrigation systems and crops with high demand of water and with high yields (corn, alfalfa, rice ...). Therefore, as a result of modernization, water management has resulted in profound changes. For instance, water distribution is handled automatically and from distance through new technologies and softwares (ADOR). Nevertheless, modernization faces to some limitations, among which we must underline the wind in the case of sprinkler irrigation systems, farming part-time, high investment costs for the conversion to pressurized irrigation systems, and rising costs of the energy required for the functioning of the system. An important aspect in which we have placed special emphasis is the need of the construction of irrigation ponds, which are essential in the process of modernization. The ponds are used to store water and to send the pressurized water to the fields, either by gravity or by pumping systems. In addition, the ponds have increased the flexibility in the efficiency of the water use. Among the problems to which the project of the Riegos del Alto Aragón faces, we have to highlight the high costs of modernization, the elevated energy costs and the rising difficulties to regulate the rivers Cinca and Gállego, which calls into question the expansion of irrigation to the southern face of the Sierra de Alcubierre. On the other hand, the system faces several uncertainties regarding the potential effects of climate change. The current and future increases in temperature increases the water needs of crops coinciding with a moment when there is a trend to decreasing water resources, due to the hydrological effect of the expansion of shrubs and forests in mountain areas as a result of depopulation, lower livestock pressure and the abandonment of crops on hillsides