Miño.

Miño.

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Key features of the case study

The Spanish energetic policy in the beginning of the economic and industrial development of the country centered great part of its objectives on the usefulness of the hydroelectric potential of the mayority of the Spanish rivers. In this context, between the years 1950 and 1990, 939 were built in the whole world, being 46 them are in Galicia.
The Frieira dam was built in 1970 and as in the design of other big dams, regardless of environmental criteria. As a consequence, the dam has brought substantial negative efects. The "barrier effect" causes the interruption of the longitudinal continuity of the Miño river and the fish migrations.
The Frieira dam is the first obstacle of the river, as it is located at aproximately 68 km from the mouth to the Altanlic Ocean. Upstream, the continuity of the Miño river is interrupted by four more dams that stop the fish access to headwaters: Castrelo, Velle, Peares and Belesar. There are tho rivers upstream the Frieira dam, the Avia river (37 Km of main course, with an area basin of 643 Km²) and the Arnoia river (58 Km of main course and 923 Km² of basin ) and other three rivers of less entity (Deva, Cierves and Brull) that could provide refuge and spawn areas to the migratory fish.
Anyway, the Avia river is regulated by the Albarellos dam and the Arnoia river has four transversal barriers (small hydroelectric) some of them with fish passage (so far we do not have reliable data).
The Frieira dam is 33 m high with 194 m long at the top. It has a storage capacity of 44,41 Hm3 and a surface of 466 ha. The main effect is on the migration of fish species as atlantic salmon (Salmo salar), eel (Anguilla anguilla) , "reo" (Salmo trutta), lamprey (Petromyzon marinus) and "sábalo" (Alosa alosa). It has also negative effects on the populations of the naiad (Margarita sp.) and fish predators as the huron and the otter. the result is a loss of biodiversity a decrease on fish population, and a impoverishment on the social and economic benefits of the river and the activities related with fish (mainly, recreational fishing).
Previously, a passage for eels was built, with ineffective results.This project was conceived as pioneer and innovative in the context of environmental restoration, with the aim of recover the aquatic habitat and fish populations at the low Miño river.

Measures selection

For restore the continuity of the Miño river, different alternatives were considered. Finally, the construction of this elevation system was choosed.The project consisted of three well differentiated parts: the scale of troughs in the lower part, the elevation system and a restoration fish channel in the upper part.

• The scale was designed to be effective independently of the water level under the dam.The flow called to the scale is supplied from waters up the dam by means of a pipe that takes the water flow from the restoration channel itself at the height of 63 m above sea level and allows the transport by gravety. This pipe ends in a jet valve and manual working, that allows to regulate the flow and to adapt it to the needs in function of the year period and the species in period of migration.
  
• The elevation system consists of an aerobicable transport system, by means of a basket of aproximately 2000 litres of capacity, full of water where the fish fauna is transported from the capture trough situated in waters under the Frieira dam, until the restoration branch channel situated water up the dam. Its functioning is automatic, and the speed is adjustable (decreasing when loading and unloading the fish from the basket). The process of loading is made synchronizing the basket entrance movement in tne transport capture trough simultaneous opening of the basket lid and the capture rake.The distance to save by the elevation system is 250 m, and the way is therefore done in about 8 minutes.
• The restoration channel offers the fish that join in from the elevation system a route to the dam.
  
  

Since the beggining, there were some arguments against this election. The construction of this elevation system meant not a big increase in the aquatic habitat disponibility, as there are more dams upstream, and the tributories that would be gained may not be considered excellent. Also, the design of the project never took into account the movement of youth and catched fish downstream.

Success criteria

The project expected succesful results in a mid-term period (10 years). It was planned a program for monitoring the effectiveness of the project consisting in a video system for counting at the unloading area and inventories at the subasins of the river Avia and Arnoia. The indicator species would be salmon, reo, alosas, and lamprey, with the following results:

	Year 1	Year 2	Year 3	Year 4	Year 5
Salmon	150	150	300	450	1000
Reo	3000	5000	12000	25000	25000
Lamprey	1000	1500	2000	3000	3000
Alosa	30000-40000	100000-200000	> 250000	> 250000	> 250000

Hydromorphological response

The aims of this project were focused on the ecological status of the fish populations, not on recover the hydromorphological quality of the river. A second project, that is being done now, is dedicated to the contribution of the ecological flow for the lower Miño (about 60 - 80 m³/s)

Contact person within the organization

Unión Fenosa S.A., (Xunta de Galicia)

María Luisa Prada Hervella

Carretera de Monforte, S/N, ES, 32960

Telephone: +34988235211

Fax: +34988238603

E-mail: mlprada@uef.es

Website: www.unionfenosa.es

References

• The Miño at the Frieira dam, during the winter of 2010 [1][2]

Related Measures

• Install fish pass/bypass/side channel for upstream migration

Related Pressures

• Artificial barriers upstream from the site
• Colinear connected reservoir