PROJECT DESCRIPTION
BACKGROUND
It has been long recognized that obstructions in rivers such as dams cause fragmentation of aquatic ecosystems and affect fish populations. This “barrier effect” impedes the migration of fish populations, resulting in the decline and in some cases complete loss of fish species, and generates negative impacts on the whole fluvial ecosystem. Species such as steelhead, salmon and trout are particularly susceptible as they need to migrate upstream to find suitable spawning locations. Since the 1950s, most of Spanish rivers have been dammed in order to produce hydroelectric power. Between 1950 and 1990, 939 dams were built worldwide, of which 46 were in Galicia (Spain). They were constructed in a period in which environmental principles were not integrated into energy planning. Consequently, dams were built without providing passage mechanisms that would allow a variety of migratory fish species to reach their spawning areas. The Frieira Dam was completed in 1970 in the major hydrographical basin of Galicia. It had clear impacts on the fluvial ecosystem, impeding the reproductive migration of the populations of salmon, brown trout, shad, eel and lamprey, and affecting the vital cycle of other fish and mollusc species. During the migration period the adult migratory fish populations accumulated at the bottom of the dam, being unable to go further upstream to reach the upper area with suitable spawning conditions. This resulted in a major decline of these populations and a substantial loss in species richness upstream of the dam, with knock-on effects on other species and ecosystems that depend on these fish populations, especially fish predators like otter, heron, etc. In addition, fishing stocks decreased, with a negative effect on related economic and social activities.
OBJECTIVES
The general objective of the project was the restoration of the fluvial ecosystem upstream of the Frieira dam. This dam is 33m high; it is about 68 km away from the Miño River estuary (which flows into the Atlantic ocean) and constitutes the first obstruction to fish migration in the Miño River. The project aimed at correcting the environmental impact produced by the Frieira installations by providing passage facilities to encourage upstream fish migration. The expected results were the following: - Increase in the number of individuals passing over the dam (completing upstream migration) - Increase of biomass in the upstream part of the dam (reservoir and river) - Improvement of the whole fluvial ecosystem on the upstream side, favouring other animals such as mammal and bird populations - Increase in the ratio between the potential spawning area and the real spawning area upstream of the dam (at present some potential areas are not being used) - Better management of fish stocks, hence an increase in fishing related economic activities with a positive impact on local employment and rural tourism (through fishing licence sales).
RESULTS
The project involved construction of adult fish passage facilities, comprising three elements: - A fish ladder was built in the lower part of the dam, with water flow regulation that can be adapted according to water volume and energy demand. This structure allows fish to pass around the dam barrier by swimming and leaping up a series of relatively low steps into the waters on the other side of the dam. - An elevator system was constructed to transport the fish. After carrying out various technical studies, the solution adopted was a cable-car system (250 m long), where the fish fauna is transported in tanks from the capture pools to the restitution channel situated upstream of the dam. - Restitution channels were built (125 m long) in order to guide the fish from the elevator device towards the reservoir pool. Despite significant delays in the construction phase, mainly due to weather conditions and legal constraints (construction licences), the general objective of constructing a passage system for fish populations was successfully achieved. However the further benefits expected to be generated through the implementation of this project, such as the recovery of fish and other species populations upstream of the dam, and the social and economic benefits, are unlikely to be clearly noticeable in the short term. For example, it is expected that the salmon population will increase in 5 years from 150 to 1000 individuals. Monitoring is being carried out to assess the real effectiveness and impacts of the project. The beneficiary believes that this type of investment could generate notable benefits for the whole region, both environmentally and economically, obtained over a 10 years period following the construction of the passage structure. The project is innovative because it is the first time that a passage mechanism has been built in a big dam in Galicia. Although a variety of technologies have been used in other countries, there are very few examples where these deal with old and large-scale dams. In addition, it constitutes an example of integration of environmental requirements into economic considerations, by means of minimising the negative environmental impacts generated by the execution of an economic activity. These aspects respond to the principles and priorities of the 5th Environment Action Programme, and in general to the basic themes of EC environmental policy. The fundamental techniques of the project are applicable to any dam that impedes fish migration, including constructions that have no effect on migratory populations but do interrupt the continuity of continental aquatic ecosystems. If the monitoring data demonstrates the success of this project, it could serve as a model to be used in other river barriers at national and international level. The success of the project could also possibly influence the adoption of environmental principles for the remaining 17 hydraulic centers in Galicia owned by Union Fenosa.
