A REVIEW ON 12 MONITORING SURVEYS OF SEFIDRUD DAM

Sefidrud dam is located in Manjil, Gilan province, Iran, on the Sefidrud River. This concrete structure has a total length of 425 meters and a height of 106 meters, with reservoir capacity of 1100 million cubic meters. GPS and Microgeodesy group from surveying department of Mahabghods Consulting Engineers Company has performed monitoring project of this dam through four separate networks: Horizontal reference network in downstream area of the dam (off-dam network) Monitoring network to detect horizontal displacements of the dam (on-dam network) Leveling network to complement the two above networks A collimation network to have a close study on the movements of the dam in three sections along the dam longitudinal axis. All of the networks have been surveyed at least for 12 times, but sometimes not simultaneously. The off-dam network consists of 6 control points, distributed well in downstream area and is interconnected through 28 distance, 28 direction and 28 zenith angle observations. A minimum constraint adjustment was accomplished to both; detect outliers and acquire consistent results. Maximum dimension of error ellipses was 0.44 millimeter in 95% confidence level in 12th epoch. On-dam network, which consists of 5 points and also 6 points of collimation reference stations, was observed from two stations of reference network. This network consists of 38 distance, 77 direction and 64 zenith angle observations. Maximum dimension of error ellipses was 1.93 millimeter in 95% confidence level in 12th epoch. Leveling network, consisting of two loops for two; reference network and monitoring network was conducted. Off-dam and on-dam leveling networks include 25 and 56 points respectively. and finally the collimation network, which consists of three separate lines, was monitored from six collimation reference points, two for each. This network includes 6 stations and 43 deflection angle observations. This paper presents these 12 epochs of the survey and shows the consistency of the results from all networks. It is also evident that the collimation network shows the spindly movement behavior of the dam, bending in the middle toward downstream.