An investigation on estimation of vertical changes at the fill dams by precise trigonometric levelling method

At the beginning, the dams had been built in order to meet the demands and water flood control. Later on they were designed as electricity production oriented in order to meet the increasing energy requirement, especially as a result of the rapid increase in population and technological and cultural developments. That situation came with the result that larger dams must have been built. Since the big buildings like dams are under burden there exists exchanges in structure and environment. These kind of changes are called as deformation. Some deformations which are over the limits may cause great tragedies with loss of life and property. Therefore, it is very important to observe the changes in the environment of dams and take precautions. In this study, the possibility of estimation of vertical changes by using precise trigonometric levelling method for the fill dams has been researched. Thus, at the Pabuçdere dam, which is choosen as application field, the geodetic results that have been taken during June 2003, September 2003 and September 2004 periods are seperately adjusted and analysed. Precise geometric levelling and precise trigonometric levelling results have been compared. As a result of evaluations of precise geometric levelling measurements, for a 100 m long levveling path, an average of 0.15 mm accuracy has been reached. On the other hand, at the results of trigonometric levelling measurements, that are made in the same periods, an avarage of 3.22 mm accuracy has been reached for the same levelling path. To conclude at the end of all these research, comparisons and examinations, with the facility of high accurate electronic tachometer measuring, precise trigonometric levelling method can applied for fill dams in the case of vertical changes between different measuring periods are in a few milimeters. Keywords : Deformation measurements on dams, precise trigonometric levelling, precise geometric levelling