Tail bays (TB) of Gabčíkovo Water Work belong to the biggest in Europe. They enable to overcome the altitude difference of water levels between the incoming and outlet chanel in the range of 16 – ...23,3 m. On the above heading are installed segment shutters; the bottom heading is locked with rotating gates. With a huge amount of water, one tail bay is filled up in 18 – 22 minutes to the high of 20 m. The rising water pressure affects the deformations of gates, whose width is 2 metres and weight is 435 tons (http: //mesto.sk, 2004). The previous gate deformation measurements were determined only in some discrete points on the gate. But, no method of deformation measurement on the whole area of the gate at many points was used so far. In the engineering surveying was used a laser scanning technology for the purpose of documentations. In a range of international projects between the Geodesy Institute of Technical University in Munich and the Department of Surveying of Slovak University of Technology in Bratislava, an initial practical knowledge the gate deformation measurement of the right tail bay at the Gabčíkovo Water Work was obtained by using the laser scanning technology (LST). The new laser scanning technology, characterized with the area data acquisition of high density, satisfied the accuracy and the short time of acquisition was used for the first time for a purpose of the gate deformation measurement of TB. The HDS 2500 laser terrestrial scanner fy Leica Geosystems was used with the variantion of the point position determination of 6 mm for the 50 m distance (http://www.cyra.com, 2004). Measurements with LST were carried out on the airy side of the bottom TB. According to the time influence of individual water level altitudes two types of measurements were carried out. At static anditions, the measurements where scanned at aconstant water level altitude (19,3m, 13,0 m, 9,4 m a 4,4 m). Whole gates were scanned by two scans with a raster of 10×10 cm per 150 seconds. The significant transverse deformations of the bottom TB gate are at 9,4 m in the range of 1,5 cm – 2,5 cm – they are shown first of all in a bottom half of gate by the water level altitude of 13,0 m in the range of 1,5 cm – 3,0 cm. By a state of maximal loading of TB gate are deformations in a range of 3,0 to 3,7 cm in a bottom part. Dynamical measurements are carried out with a repeated scanning of a part of gate during the process of filling and emptying of TB, i.e. rising and lowering of water level altitude. The velocity of rising or sinking of water level altitude in TB is ca 1,6 m per minute. To have a constant ratio of gate loading in the time of one scan, the scanning was with a raster of 8×8 cm per 30 seconds for only one selected part of the right gate (a tight vertical strip in a middle of TB), in which the biggest deformations were predicted. Dynamical deformations of a part of TB during the process of filling and emptying is presented by the animation from the 49 stages (loading states). The water level altitude difference between two stages is 80 cm for 30 seconds. The laser scanning technology introduces a new method of deformation measurements. Its advantage is the measurement velocity and the determination of deformations in the whole area of the measured object by static as well as dynamical measurements.
