GNSS methods in dam monitoring: case studies and future perspectives

GNSS receivers are nowadays commonly used in monitoring applications, e.g. in estimating crustal and infrastructure deformations. This is basically due to the recent improvements in GNSS instruments and methodologies that allow high precision positioning, 24h availability, semiautomatic data processing. In this paper, we use GNSS technique to monitor dam deformation behaviour comparing results with outcomes from pendulum observations that thanks to their reliability and high accuracy can be considered as reference. The study has been carried out for two dams in Sardinia: the Genna Is Abis on Rio Cixerri, and the Eleonora D’Arborea called also Cantoniera dam. Appropriate analytical models of dam deformation depending on time, reservoir water level, air and water temperature have been estimated using pendulum data (for Genna Is Abis dam) and GNSS data (for Cantoniera dam). Both reference models were able to properly fit respectively pendulum data and GNSS data, with standard deviation of residuals lower than one millimeter. Furthermore the Genna Is Abis reference deformation model deduced by pendulum was compared with estimated displacement from GNSS observations and standard deviation of the residuals was still lower than one millimeter. For the send model estimated at Cantoniera dam the comparison with pendulum data gave residual with mean around zero and standard deviation of lower than two millimiter. These encouraging outcomes open new perspectives in the study of deformations of structures that foresee the GNSS technique as complementary monitoring instrumentation especially for medium-long time intervals.