Nery Zapata y Daniel Isidoro han guiado una visita técnica de los integrantes del máster internacional "Land and Water Development for Food Security" ►, máster conjunto de la University of Nebraska-Lincoln (EEUU) ► y el Institute for Water Education (IHE) ► de Delft (Holanda). Durante la visita, los estudiantes han podido conocer el sistema de riegos del Alto Aragón y visitar la Comunidad de Regantes de Almudévar.
Nery Zapata es investigadora en el Departamento de Suelo y Agua de la Estación Experimental de Aula Dei (CSIC). Es experta en diseño y manejo de sistemas de riego (gravedad y presurizados) mediante estudios de campo y herramientas de simulación, así como en el manejo de dichos sistemas tanto a escala de explotación individual y de distrito de riego.
Daniel Isidoro es investigador en el Departamento de Suelos y Riegos del Centro de Investigación y Tecnología Agroalimentaria de Aragón (CITA). Es experto en contaminación de agua en regadíos, especialmente en nitratos, salinidad y pesticidas.
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Summary of the visit
Spain accounts for almost a third (3.365 M ha) of all the total irrigated area in the whole of the EU (10.475 M ha). According to FAO AQUASTAT the potentially irrigated area in Spain is almost completely utilized. Irrigation is a strategic water use sector in Spain, since it consumes the largest share of the National water resources (estimated at 23,000 Mm3), and uses 50% of the water kept in reservoirs and dams (Pindado, 2005). Irrigation is also a key part of the agricultural sector, since it accounts for 60% of the total agricultural production (i.e., 13,000 M€ out of an estimated 20,500 M€), and 80% of the total agricultural exports (López-Gunn, 2012).
The Ebro river basin has approximately 0.9 Mha of irrigated land divided in several irrigation systems, the fourth largest are: Riegos del Alto Aragón (124.000 has), Canal de Aragón y Cataluña (104.000 ha), Canal de Bardenas (82.500 has) and Canales de Urgell (70.000 has).
“Riegos del Alto Aragón (RAA)” irrigation project is located in NE Spain, in the central Ebro River Basin (Fig. 1) Development of this irrigation project started in 1915, intensified in the 1940s to 1960s and is still ongoing. The current irrigated area is 123,354 ha, covering a territory of 2500 km2, and with an altitude ranging from 200 to 425 m above mean sea level. RAA is distributed among five sub-basins: Gállego, Flumen, Alcanadre, Cinca and Ebro. Irrigation water originates at the Central Pyrenees Mountains and its quality for irrigation is high (electrical conductivity <0.4 dSm−1). The local climate is semi-arid Mediterranean continental, with a mean annual temperature of 14.5 ºC, and an annual precipitation oscillating between 300 mm in the South and 450 mm in the North. A dry period typically extends from July to September. The annual reference evapotranspiration (Hargreaves and Samani, 1985) varies from 949 mm in the North to 1149 mm in the South. The average wind speed (at 2.0 m height) is about 1.9 m s−1 in the North and 2.6 m s−1 in the South (Lecina et al., 2010).
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| Figure 1. Location of Ebro River Basin and the Riegos del Alto Aragón (RAA) irrigation project in Spain |
The RAA project uses six head reservoirs (Búbal, El Grado, Lanuza, Mediano y Ardisa and Sotonera) with a total storage capacity of 930 Mm3, 223 km of main canals, 2000 km of secondary canals, and 3000 km of drainage collectors. Almost all irrigation canals and ditches are lined. In addition to irrigation water delivery, the project supplies domestic water to a population around 70000 inhabitants and 800 livestock farms.
Around 75% of the total irrigated area (91,000 ha) are irrigated by pressurized systems and the rest 25 % (around 30,000 ha) are surface irrigated.
La Sotonera reservoir is close to the Gállego River, constituting a lateral dam that has a storage capacity of 189 Mm3. Its construction started in 1920 but it was not finished until 1963. La Sotonera is a key part of the RAA system, because it is the origin of the Monegros canal (capacity of 90 m3 s-1, 133 km length) which supplies water to a large part of RAA system.
Figure 2. Location of the VID in the Ebro Basin in north-east Spain.
Location of the gauging stations to measure the volume and quality of the water returns flows. (Jimenez-Aguirre et al., 2018)
The Violada irrigation district (VID, Fig. 2) VID is located in the central Ebro River basin, in the lower reaches of the 19,637 ha “La Violada” Gully watershed (north-east Spain; latitude: 41°59’ – 42°04’ N; longitude: 0°32’ – 0°40’ W). The VID is part of the RAA system. Local altitude ranges between 414 m in the north and 345 m in the south-west. The whole district (irrigable and non irrigable area) occupies an area of 5,282 ha. It is delimited by the Monegros, Violada and Santa Quiteria canals (Fig. 2), and counts on 3,744 ha of irrigated land. These canals supply irrigation water with excellent quality (EC < 0.4 dS/m) from the Gállego River, tributary of the Ebro River.
The irrigation modernization projects performed in Spain in the last 15 years amount to 1/3 of the irrigated area in Spain. Most of these projects implement remote control and surveillance systems.
The irrigated area of the VID was recently modernized to pressurized irrigation implementing a remote control and surveillance system. The largest part of the irrigated area has been equipped with solid-set sprinkler irrigation systems (around 90%). The modernization process has increased the presence of high-water-requirements crops, such as corn, alfalfa and double cropping schemes. As a consequence, the irrigation water demand has increased and so has the energy demand. In the 2011 irrigation season the crop pattern was: 40% of double cropping (barley/corn principally); 15% corn, 23% winter cereals, 12% alfalfa and 10% other crops (Fig. 3). In that irrigation season, the total water consumption was 21,471 Mm3, with a total energy consumption of 6,057 Gwh. The water application cost in the VID (water + energy + irrigation system pay-back) amounted to 30-40% of the total farming costs.
Figure 3. Crop distribution pattern in the 2011 irrigation season at a plot scale (Stambouli et al., 2014).
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The added value of telemetry and remote control systems lies in that real-time, plot-level data are continuously produced and stored. In some irrigation districts, as the VID, these systems go beyond the hydrant level, and reach the irrigated block level. These data can be effectively used to promote excellence in irrigation water and energy management. Despite these possibilities, current use of this technology remains incipient and restricted to basic remote control operation and general network surveillance and alarm management. Within this general scenario of low use of remote control and surveillance technology, the VID is a clear exception. In this irrigation district all irrigation scheduling is performed at the district offices, and irrigation is programmed for all irrigated plots from the remote control and surveillance system.
| Figure 4. Changes observed in water use and salt and nitrate loads in VID |
in two periods dominated by high intensity corn cropping: 1995-98 and 2011-15.
Irrigation programming and execution is consequently fully automated and controlled by district personnel. Water users sustain a dialogue with district personnel to adjust irrigation programming to personal preferences. The goals of VID irrigation scheduling are minimizing energy and water use. Energy costs are subjected to strong intraday, intra week and inter month variations. Optimum irrigation decision making can minimize energy costs. Sprinkler irrigation performance is strongly affected by meteorological conditions. In the presence of strong winds, high temperatures and low relative humidity, irrigation water use cans double crop water requirements. Selecting the right meteorological conditions for irrigation will therefore minimize water and energy consumption.
The modernization of VID (2009-10) has reduced the use of water for irrigation in relation to the previous flood-irrigation practice under high ET crops (maize and alfalfa, years 1995-98) by 39% while intensifying cropping patterns (With the introduction of double crops). Consequently, the volume of drainage has decreased by 71%. This leaves a volume of non-diverted, high-quality water of 20 hm3/year, available for other uses (like urban supply or natural flow). The estimated crop ETa has increased by around 10% and wind-drift and evaporation losses (WDEL) has shown up under sprinkler irrigation Fig. 4). The indices of water use at district level have increased flowing this enhanced water use: the consumptive fraction [CF = (ETa + WDEL) / (Irrig + P)] has increased from 55% to 89%, while the estimated irrigation efficiency [IEf = (ETa – Pef) / Irrig] has increased from 51% to 80%.
The concentration of salts in return flows has remained more or less constant (as the waters are saturated in gypsum) but the mass of exported salts has decreased from 19.9 Mg/year in 1995-98 to 6.3 Mg/year in 2011-15 (65%). The concentration of nitrate in the return flows was very high in the 1990’s (around 37 mg/L), in spite of the inefficient irrigation and its diluting effect, and has remained similar from 2011-15 (31 mg/L), but showing an upward trend (Fig. 4). The experience in other sprinkler-irrigated areas grown with corn suggests that NO3 concentration will increase along time, although the load of N exported with remain relatively low.