Ladon dam (Greece) deformation and reservoir level fluctuations: evidence for a causative relationship from the spectral analysis of a geodetic monitoring record

Three different spectral analysis techniques, namely Discrete Fourier Transformation (DFT), Lomb normalized periodogram analysis and fitting of trigonometric/polynomial functions, were used to analyze a long (>30 years) geodetic monitoring record consisting of the horizontal and vertical displacements of six control stations established on the crest of the Ladon concrete dam, in order to identify whether reservoir level fluctuations are responsible for dam deformation. The displacements of the dam were very small (up to 7 mm), statistically significant against random errors and maximum at the middle of the dam. There was no apparent linear correlation between dam displacements and the reservoir level. On the contrary there was evidence of fluctuation in the amplitude of displacement. The presence of periodicity in our data was confirmed using the autocorrelation function. The DFT, Lomb normalized periodogram and trigonometric/polynomial fitting revealed that horizontal and vertical displacements of three control stations at the middle of the crest of the dam correspond to a 12 month period, similar to that of the fluctuations of the reservoir level, indicating a causative relationship between hydraulic load and dam deformation.