Gerlos power station/Gmund dam - stabilization of a reservoir slope (Grasegger slope)

The reservoir Gmund with a capacity of approximately 900,000 m3 is located about 10 km west of the village of Gerlos. The reservoir is connected with the power house Gerlos in the Zillertal, having a head of about 610 m. For increase of power from 65 to 200 MW the power house Gerlos was extended and the flow rate of the adapted power tunnel was raised from 14 to 42 m3/s maximum. The effect of the higher draw-down rates on the reservoir slopes has been tested in September 2004 with a highspeed draw-down with rates up to 5 m/h. As a result of this trial a landslide with an estimated volume of 10,000 m3 occurred on the Graseggerhang. The landslide showed the necessity of an effective slope stabi-lization of the Graseggerhang for a continuous unlimited reservoir management in the future. After a comprehensive investigation it was decided to build in a supporting fill, consisting of rock mass of a maximum grain size of 65 cm. The support fill with a volume of about 100,000 m3 was built in from October to December 2006 and the operation of the power plant Gerlos II started directly afterwards. For the long term surveillance of the support fill one inclinometer and several geodetic measuring points have been installed.