Closure of the Old Bottom Outlet of Lucendro Dam
(December 2006)

Lucendro is a buttress dam owned by Atel Hydro Ticino Ltd with a height of 73 m. When it was constructed, an 80 cm diameter steel pipe with a bellmouth inlet was integrated as a bottom outlet. The only gate provided is a sluice valve.

Later a new tunnel type bottom outlet with about tenfold capacity has been constructed. As the sluice valve of the old bottom outlet is ageing and represented a certain safety risk, it was decided to definitively close the old bottom outlet. In 2005 Colenco elaborated a number of different concepts for this.

The intake to the headrace tunnel is approximately 20 m lower than the dam. Therefore, the reservoir is, in the normal operation of the scheme, regularly lowered below the level of the old bottom outlet. Thus, the best concept revealed to be the filling of the bellmouth inlet with a concrete plug when the reservoir level is low.

The bellmouth to the old bottom outlet. The downstream formwork is being fixed.		The concrete was delivered by helicopter and cast directly from the bucket attached to the helicopter.

In January 2006 Atel Hydro Ticino Ltd. mandated Colenco to prepare the necessary documents for the approval of the project by the Swiss Federal Office of Energy SFOE. The latter approved the project February 23. In springtime 2006 the reservoir was low enough and in the middle of May, after extensive evacuation of snow, the works were executed by the contractor Berther from Disentis.

After completion of the works the sluice valve has been opened. Apart from some drops the plug is completely leak proof. After preparation of a final report and as-build drawings the project could thus be successfully completed.

Helmut Stahl - Hydropower Plants

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Colenco Info November 2006
Selected topics presented in the Colenco Info give an insight into some of our latest projects.