Historical Heritage Monitoring at the El Retorno hydroelectric power plant

We have recently had the opportunity to work on the Assessment of Historical Heritage Conditions for the project “Demolition of dams and gates and sealing of the bypass tunnel of the El Retorno hydroelectric power plant” commissioned by the company Tragsa and the Jucar Hydrographic Confederation.

The hydroelectric project called “El Retorno”, currently out of service, is located on the Cabriel River, in the municipalities of Casas Ibáñez, province of Albacete, and Venta del Moro, province of Valencia. Specifically, the gate bridge, the outlet, the bypass tunnel, the loading chamber, the power plant building and the discharge channel are located at the northern end of the town of Casas Ibáñez, while the bypass dam develops between the two municipalities, the right side in Casas Ibáñez and the left side in Venta del Moro.

The project proposes that the dismantling of the dam related to this dam or its conditioning to turn it into a passage permeable to fauna would improve the loina or madrilla del Jucar (Parachondrostoma arrigonis), a species included in the category of “endangered” in the Spanish Catalogue of Threatened Species (Decree 139/2011) and in the state of conservation of the Cabriel River, included in the Park of the same name and in the Natura 2000 Network. Added to this is the fact that this dam called El Retorno is catalogued in the Archaeological Charter of the municipality of Casas Ibáñez under the number 07020240116 as part of its industrial heritage, which makes this study inevitable.

Methodologically, the study has sought to collect data as reliable as possible and to synthesize them. Thus, in the event that the object - especially in the case of buildings - must be destroyed, due to the impossibility of maintaining and conserving it, as is the case, a more complete documentary record must be made than a simple inventory, to preserve all possible information about it for possible subsequent studies. This must collect information about the building or complex, but also about the context in which it is located and in which it has been developed. The registry, therefore, corrects documentation that is about to disappear.

As we have mentioned before, the structures affected by the actions described in this study are made up of:

• The gate bridge.

It consists of five openings with four gates framed between piles of concrete masonry. Concrete piles are columns with an approximately rectangular section in the upper half, which pass to an almond-shaped plan in the lower half, when the piles become a slab or part that is added to the piles, upstream and downstream, in a curved or angular shape, so that it can cut off the water from the stream and distribute it equally on both sides of them. These constructions make the bridge piles offer less resistance to the drag force generated by water.

Piles and tajamares upstream of the dam.

Through the crowning of the piles, a concrete walkway is developed on which the remains of the gate actuation mechanisms are arranged, basically composed of wheels and gears that allow them to be opened and closed, as well as lattice joists that connect the different elements.

Metal mechanisms of the bridge and walkway between pillars, central area.

• Capture and bypass channel.

The catchment, located on the right bank, consists of two gates placed in a direction perpendicular to the bypass dam. These are topped by a small bridge, on which are the metal drive elements, which, as in the case of the main bridge, consist of wheels and gears for lifting them.

Gate mechanism and gateway for access to the collection channel.

The bypass channel is developed in a rectangular tunnel with a width of 4.50 meters and a variable height of between 2.25 and 3.50 meters. The wet surface is covered with hydraulic mortar, the upper part is not coated, leaving the rock in the ground visible. The channel has a length of 156.00 m. At the end of the channel, at the entrance to the loading chamber located in the “El Retorno” power plant, the tunnel widens to 12.00 meters.

Bypass channel inlet nozzle.

With regard to the element at hand, we must point out that for some time (Arroyo, 2012), the hydraulic power of Jucar had been used by the numerous mills and batanes that lined its banks, as mentioned in the Topographic Reports of Philip II (16th century), Madoz (1846-1850) or Roa and Erostarbe (1891-94)

Many of these mills were transformed into mini-hydroelectric power plants to supply nearby areas, but through local networks with little economic and territorial impact.

The first electrical facility built was the Salto de Molinar (1909), on the Jucar River, and at the same time the electric power transmission lines that linked it to Madrid and Valencia were built; two milestones mark this plant: it is the most profitable of those that were operating at the time in Spain and, for the first time in the world, it was possible to transfer 16,000 horsepower over a distance of 240 km, the one existing between the power plant and Madrid.

Thus, in just under thirty years, the Júcar-Cabriel system had been among the main hydroelectric complexes in the peninsula. In 1930, the basin of both rivers was already the third in electricity production in Spain, after the Ebro system and the Cantabrian waterfalls.

In this case, the concession to use public waters of the Cabriel River for industrial use, to produce electrical energy in the C.H. of “El Retorno”, was granted by Royal Order of September 9, 1930 to the Almameñe Electric Company. On November 10, 1969, by means of an award in payment of debts, granted by Eléctrica Almansena, S.A., to the notary of Almansa D. José Gabriel Grau Soto, the ownership of the project passed to Hidroelectrica Española, S.A. Subsequently, on June 6, 1989, a file was initiated to cancel the hydroelectric project of “El Retorno”, as it was out of use. The file was decided by the Minister of Public Works, Transport and Environment, on December 19, 1994, to the effect of: “Declare the right to use the waters of the Cabriel River expired, for motor power and industrial uses, in the T.M. de Venta del Moro (Valencia) and Casas Ibáñez (Albacete), Central “El Retorno”, whose original concession was granted by R.O. on September 9, 1930 in favor of the Almameñe Electric Company”.