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Manzanares

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This case study has been described by Arenillas-Girola(2008).^[1]. Here below we present the abstract of the paper:

Manzanares river, in the Tajo basin, has its source within the mountains of the Sistema Central chain, located in the northern part of the Madrid region. During the first few kilometers, the river flows across an area where the granite geology and the pristine nature are so interesting and unique, that has been declared as a Regional Park and as well as an UNESCO Biosphere Reserve since 1992. In the heart of this area, during the decade of the 40s, a dam was built in the Manzanares river in order to supply water to the village located downstream. Year by year the dam has accumulated such a big quantity of sediments coming from the granite banks and slopes, that at the end of the century it was completely full of sand, in such a way that it became useless and an ecological disaster. The Confederación Hidrográfica del Tajo (the river basin authority) in collaboration with other authorities, stated as an achievement this dam demolition. The target was to give back to the river the natural features it had before the dam construction. As the dam was located in a protected area, one of the goals was to preserve -as far as possible- all the natural values of the surroundings, trying to accomplish all the works without damaging the river bed, the banks and the areas nearby, keeping as well flora and landscape features. The works were carried out in three stages: in each one the target was the demolition of a part of the dam through different controlled detonations and then the waste removal. This task was carried out through an helicopter, as the path between the river bank and the granite slope was so narrow that a heavy machine would have caused a significant destruction of it. The last goal was to restore the river bed and banks that had been affected by the dam -while existing- and the demolition works. During this stage the tasks were just a light reforestation and not much more, as the river flow was able to remove the last sand particles that had been retained near the old dam.

References:

1. ↑ Arenillas Girola, Lidia, 2008. The Manzanares river restoration (northern Madrid-Spain): demolition of an obsolete dam and riverine ecosystem rehabilitation. 4th ECRR Conference on River Restoration, Venice, Italy, June 2008.
   DOWNLOAD full paper Media:S1_4_Arenillas Girola.pdf