Investigation of the relationship between rainfall and long-term settlements of earthfill dams based on geodetic measurements: the case of Pournari I dam (Greece)

Ageing earthfill dams become vulnerable to weather phenomena such as rainfall and flooding, with severe consequences, economic and life threatening, to the communities living downstream. A better understanding of their long-term behaviour and the factors affecting it, is crucial. A unique data set was used, consisting of the crest settlements of an earthfill, central clay core dam, the Pournari I dam in Greece, and the rainfall height values at the dam site between 1981 and 2015. The dam is 107 m high and its construction was completed in 1981. In previous studies the settlements of this dam, including rates, were found to be within limits and compliant with empirical relationships derived for dams of this type. In this work we remove the effect of primary consolidation and creep from the settlements and attempt to study the relationship between the residuals and rainfall. We find that consolidation was completed within 4 years since the end of construction (by 1985) and residuals of all points on the crest appear to follow the same evolution pattern. While no direct relationship could be established between the actual settlement observations and the rainfall, residuals seem to have maximum correlation with the cumulative rainfall height over a period of two months before the settlement measurement epoch. Our findings most likely represent a threshold value of rainfall above which the dam seems to be responding rather than a time duration over which rainfall plays an important role to the settlements of the dam.