Yesa Reservoir
The Yesa Reservoir is located in the Pyrenees, and is formed with the damming of the Aragon River, in the Navarre town of Yesa, although the largest area of the reservoir is located in the province of Zaragoza, extending from east to west. It is located to the northwest of the Aragonese province of Zaragoza and to the east of Navarre. Most of it floods lands of the Berdun Canal, in the Aragonese region of Jacetania in the municipalities of Sigüés, Ruesta, Escó, and Tiermas. It is known by the nickname Mar de los Pirineos and is located at the entrance of the aforementioned. It is the largest navigable area of Aragon and it is the source of the Bardenas Canal that transfers water to the Ribera area south of Navarra and irrigates the Bardenas Reales and the Cinco Villas region of Zaragoza. It is also used for water supply and as a power station.
It has a capacity of 446.86 hm³, reaching the following elevations: minimum, 435.00 m; crest, 490.00 m; spillway, 482.61 m and maximum normal reservoir elevation of 488.61 m. The length of the tail end of the reservoir is 10 km with widths varying between 1 and 2.5 km. It occupies an area of 1900 hectares.
It was inaugurated in 1960 and caused the abandonment of several towns: Ruesta, Tiermas, and Escó with an affected population of more than 1500 people. Collaterally, due to the expropriation and planting of pine trees to prevent the siltation of the reservoir, the following upstream towns were affected: Larrosa, Villanovilla, Bescós de Garcipollera, Bergosa, Acín, and, Yosa de Garcipollera in the Garcipollera valley, now belonging to the municipality of Jaca and Cenarbe in Villanúa. 2408 hectares of farmland were flooded, of which 1000 were of very good agricultural quality.
On the other hand, the waters of the Aragón river transferred by the Bardenas canal to the region of Cinco Villas and the Bardenas Reales have led to the creation of 81 107.64 ha of irrigated land, 18 941.61 ha in the province of Navarra and 62 166.03 ha in the province of Zaragoza, which, together with the supply to the 54 777 inhabitants who depend directly on the system, demand an average annual flow of 467 hm³ of water. This has led to the creation of some fifteen colonization villages, which are home to some 1267 families, many of which come from the villages evicted when the Berdún canal area was flooded. Such is the case of El Bayo, to which many families from Tiermas had to emigrate.
Dam
The dam is located 400 m from the urban center of Yesa in a northerly direction. It is a gravity dam with a straight ground plan built of concrete with a vertical slope at the top and a stepped slope, with steps 2 m high and 1,60 m wide at the bottom, which generates a slope of 0,78. It is equipped with a surface spillway located on the left bank and formed by four large mouths, intermediate and bottom drains. It has two intakes for the hydroelectric plant and another for the Bardenas canal.The length at the crest is 398 m, with a height over foundations of 76.5 m and over the riverbed of 62.1 m; the width at the crest is 7 m, of which 6.5 are dedicated to a road. It consists of a perimeter gallery with five accesses, three of which are at the foot of the dam and the other two at the top, which join at elevation 460 with a horizontal gallery in the abutments, which can be accessed from the dam parameter, next to the intake for the canal.
Spillway
The dam is equipped with a spillway system consisting of four shafts with independent tunnels of an average length of 600.5 m ending in a common damper for all of them. The four spillways are equipped with concrete gates with a floating sector of 20 m in span and 6 in height. They are located on the left side of the dam. The height of the fixed lip is 482,61 m and they allow outflows of:- In normal regime, 2240,00 m³/s.
- In flood regime, 3060,00 m³/s.
Drainage
- Intermediate: it is located on the intake of the central one foreseen at the foot of the dam at 448,40 m level. They are two conduits of 1 m of diameter. It uses two Howell-Bunger type valves with fixed cone. The capacity of drainage is 38,5 m³/s.
- At the bottom: they are located at the foot of the dam at an elevation of 428.0 m on the left side, on what was the old bed of the Aragón river. They are two pipes of 1.50 x 2.00 m governed by valves. The total capacity of the outfall is 172 m³/s.
Intakes
- Intake of the Bardenas canal: at 453.35 m elevation, located on the left side. It consists of three 2 m diameter pipes governed by ring-seal valves and Tainter type gates. The total normal flow is 90 m³/s.
- Intake for power plant at the foot of the dam: it is located at 448.4 m and consists of two pipes of 2.5 m diameter that are governed by wagon gates from the upper part, in the lower part they are closed by a blind flange. The dimensions of the gates are 2,5 x 2,5 m.
- Intake for the power plant next to the Bardenas intake: of the same type as the previous one, consisting of two 3 m diameter pipes. The dimensions of the gates are 3 x 5 m
Reservoir
The crest height is 490.9 m, the spillway height is 482.61, while the maximum filling height in normal situation is 488.61 m and 490.00 m in floods. The minimum level of use is 453.35 m, while that of the riverbed is 427.90 m with the bottom outlet at 428.00 m and the intakes of the Bardenas canal at 453.35 m.
The sheet of water can be accessed from the vicinity of the dam, on the left bank, through an entrance that leads to a pebble beach.
History
Background
The use of the Aragón river has been considered since the Middle Ages: as early as 1498 a proposal was made to the King of Aragón Ferdinand the Catholic to divert water from the river for use as irrigation by the Council of Tauste. In 1622 it was proposed to build a canal to Bardenas to irrigate the lands of an abbey that was planned to be built there. In 1702 the engineer Josef Estorguia and a group of hidalgo knights launched the proposal to divert the river so that it would run through Aragonese lands, thus avoiding the payment of tariffs and tolls to the Navarrese. 54 years later, in 1756, a project was drawn up for the construction of a canal that, rising in Tiermas, was to irrigate the Aragonese region of the Cinco Villas. Soon after, another project was presented, this time by Captain J. A. Monroy, who proposed a canal that would irrigate the region of Cinco Villas and Bardenas, with a total of 15 228 ha of irrigated land, as well as the construction of 18 new urban settlements.In 1865 a company was created for the construction of an irrigation canal to go down to the Bardenas. The project was carried out by Antonio de Lesarri. The society would be in charge of the construction in exchange for the use of the water and the irrigators paying the corresponding alfardas. In 1880 the concession was declared null and void, since the works had not begun.
In 1902 a Royal Decree of 25 April proposed a National Plan of Hydraulic Works in which a hydraulic complex appeared, consisting of the Bardenas de Yesa, Foz de Biniés, Salvatierra, and Usún canals, each of them with a reservoir. This complex would generate an irrigated area of 30 000 ha in several towns of Navarre and Zaragoza. The reservoirs would be located as follows: Yesa, where the current one is located; Foz de Biniés in the waters of the Veral river; Salvatierra, on the Ezka River, Usún would be located in the Salazar Valley, 6 km from Lumbier. Along with this proposal were also those of the Canal Imperial de Aragón and the Lodosa Canal, which made the need to dam the Aragón and its tributaries more evident.
On 2 March 1909 the Ebro Hydraulic Division was commissioned to study the project for the Yesa Dam. This project was carried out by the engineers Cornelio Arellano, first, and then Manuel Abascal, who completed it in 1912. The canal project was not approved until 1917. The dam designed was a 53-meter-high gravity dam.
Project
In 1923 a new project was commissioned, drafted by the engineers Félix de los Ríos, Mariano Vicente, and Antonio Colom, who carried out the study based on an irrigable area of 130 000 ha, to contribute to the Ardisa dam with 400 000 million cubic meters per year and to supply drinking water to Zaragoza. This proposal was included in the linking of the three large rivers on the left side of the Ebro, the Aragón, the Gállego and the Cinca.On 7 May 1926 a Royal Order approved the Yesa Dam project, making it compulsory to respect the uses and exploitations downstream of the dam. The same team that conceived the dam also planned the Bardenas canal, presenting their work on 29 December 1924. This would be approved eight years later, on 30 June 1932, by a Resolution of the General Directorate of Hydraulic Works. In 1926 it was estimated that Yesa reservoir would only be used for irrigating of the Bardenas and the Cinco Villas region, and its possible contribution to the Imperial Canal of Aragón was rejected. In the 1st General Plan of Works and Miscellaneous Works of the Ebro Hydrographic Confederation, in 1926, the construction of Yesa reservoir was proposed. This would have a capacity of 470 hm³; destined for the Bardenas canal and the irrigation of the farming area of the basin itself, some 15 000 ha, although the possibility of contributing to the Imperial canal was still being discussed so that this would free up resources for the Lodosa canal. The forecasts for the Bardenas canal, which, starting from Yesa, was to reach Ardisa, were for a dam outlet of 60 m³;/s, of which 39 would reach Ardisa.