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Bottom drains are one of the safety systems of dams and must be prepared at all times to carry out controlled impoundments in case of safety problems in the system:

  • Damage to the dam wall caused by seismic movements or other causes.

  • Forecast of floods, with reservoirs at their maximum levels and particularly with free sheet spillway dams.

  • Establish previously programmed reservoirs, to leave enough space to laminate the avenue without creating critical situations downstream when it occurs.

Both in Spain and in the rest of Europe, dam safety committees have been updating the operational requirements for these structures, whose environmental and economic costs are so high that they do not allow their demolition and subsequent reconstruction. These requirements, among others, consist of the incorporation of bottom drainage galleries and derivation pipes of the minimum ecological flows.

The updating of the characteristics of old dams requires new technologies that allow them to meet new needs through the minimum impact on both their operation and their structure. This is where microtunnels become very important since in short periods they allow drains and pipes to be executed both through the structure of the dam itself and through the closed ones in which they are located.



  • De Franciso, Juan. Pérez-Cecilia, Diego. Execution of a new bottom drain in the La Jarosa dam without emptying the reservoir by means of a tunnel boring machine with a closed shield, in the La Jarosa dam.

  • OSEPSA. Emergency works for the installation of an intermediate intake at the Oliana dam (Lleida)

  • Royal Decree 264/2021, of 13 April, approving the technical safety standards for dams and their reservoirs.

  • Bottom drains in dams

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