Studio delle variazioni in fenomeni geofisici indotti da grandi dighe: il caso di Enguri Dam International Test Area (EDITA) (Georgia)

Responsabili di progetto

Luciano Telesca, Teimuraz Matcharashvili

Accordo

GEORGIA - SRNSF - Shota Rustaveli National Science Foundation

Bando

CNR/SRNSF 2012-2013

Dipartimento

Terra e Ambiente

Area tematica

Scienze del sistema Terra e tecnologie per l'ambiente

Stato del progetto

Nuovo

Proposta di ricerca

Dams are man-made barriers, constructed on terrain in order to control or store large amount of water in artificial reservoirs. They are highly important edifices for the generation of electricity, flood protection, irrigation, providing drinking water resources, etc. At the same time, dams are regarded as the source of high potential environmental hazard. In the case of a dam failure, the potential energy of the water stored behind even a small dam is capable of causing loss of life, great property, infrastructure, ecology, damage of adjoining regions downstream the barrage, as well as extended period of denial of the services that dams provide (Lemperiere, 2006; M. Wieland, M., Mueller, R., 2009; Wieland, 2009).
Dams can cause induced seismicity. Reservoir-induced seismicity is observed worldwide. For example, in Nurek Reservoir, Tadjikistan (Simpson and Negmatullaev 1981), in the reservoirs LG3 and Manic 3, Quebec, Canada (Anglin and Buchbinder 1985; Leblanc and Anglin 1978), in Govind Ballav Pant reservoir, India (Gahalaut et al. 2007), and especially in Koyna-Warna, India (Gupta et al. 1969). Reservoir-triggered earthquakes have characteristics (e. g. higher b-value, larger magnitude ratio of the largest aftershock to the mainshock, increase of seismicity rate with the increase of water level) that discriminate them from normal seismic events (Gupta et al. 1972). Ground water plays an important role in reservoir-induced earthquake activity. Water pore pressure reduces the normal stress within a rock while not changing the shear stress. Under any circumstances, an increase in water pore pressure means that a failure is more likely. The critical value of shearing stress may be made arbitrarily low by increasing the pore pressure. Pore pressure can increase due to the decrease in pore volume caused by compaction under the weight of the reservoir and/or due to diffusion of reservoir water through permeable rock under the reservoir. The rate of flow depends on the permeability of the rock, so this effect is not instantaneous. The increase in pore pressure takes more time depending on the distance from the reservoir. It may take years for the pore pressure to increase at depths of kilometers beneath a reservoir.
The 271m high Enguri arch dam with a crest length of 728 m was built in the canyon of Enguri river in the 1970s in West Georgia. This is the highest arch dam in the world. The Enguri dam should be considered at a high risk, because it is located in a highly seismic area, on a secondary fault of the Ingirishi active fault system; this secondary fault divides the foundation of the dam into two large blocks, thus tectonic movements are expected. The high seismic and geodynamical activities together with a high population density of the region as well as the deterioration in the maintenance of the dam and the appurtenant structures since the beginning of the 1990s has made the Enguri dam a potential source of a major man-made catastrophe in Georgia. In case of dam failure catastrophic flood in Zugdidi region is predicted, when the flood wave may reach 50-60 m.
Presently there is not a deep knowledge of the geophysical effects induced by the dam, and the goal of the present project is just to gain as much as possible a complete understanding of the behavior of the dam and its influence on the environment around. Furthermore, a based on the modern concepts in the field, focused and detailed approach in investigating the possible reservoir-induced seismicity of the area needs to be continued. Understanding and discriminating the different components in the seismicity of the area, due to the natural tectonic fault interactions and to the loading/unloading operations of the Enguri dam, is really challenging. For this reason, the use of modern methods of linear and nonlinear time series analysis is fundamental in assessing the dynamical behavior of the dam and its effects.
Within this context, the project intends to perform a detailed study of the spatial and temporal distribution of seismicity at Enguri area and give a contribution to the question of seismic effects implied by reservoir-induced seismicity. Therefore, spatial and temporal pattern of seismicity, stress field and modeling of the pore pressure diffusion due to seasonal variations of the water level in Enguri dam will be studied.
The project intends also to investigate the dynamics of earth crust tilts caused by the large dam construction and reservoir filling at Enguri. Since 1983, hourly tilt data continuously measured in the dam foundation before and after the filling of the reservoir by several tiltmeters represent an important database for recognizing natural and anthropogenic mechanisms in earth tilt generation.
Moreover, hourly measurements of tilts of the dam body (since 1997) are able to give information about deformations that the dam undergoes, as response to changing loads. Dam displacements in two horizontal directions parallel and normal to the dam crest are, in fact, continuously measured. The movements have a complex structure in time, although the annual cycle predominates.
Therefore, quantitative analysis of all such data as well as dynamical peculiarities of water level variation and seismicity around the reservoir would reveal very interesting dynamical properties of the investigated phenomenon.
The Georgian and Italian teams have a great experience in the investigation of geophysical and environmental phenomena, and natural as well as human-caused hazards. They will use and share their competence in data analysis (standard and advanced time series signal processing and statistics) to get the best understanding of the Enguri dam deformation processes and their effects on the environment around, making the project feasible and its objectives achievable.

Obiettivi della ricerca

1) To analyze the space-time dynamics of the seismicity at Enguri area.
2) To analyze the relationship of the seismicity at Enguri area with water level of the dam.
3) To develop a hydrological model for the Enguri area and to estimate the vertical hydraulic diffusivity of the area.
4) To study the time fluctuations of the earth tilt time series at foundation and tilt time series on the body of the dam using standard and advanced time series tools.
5) To provide an assessment of the hazard of the Enguri dam on the base of the results obtained through the analysis of the data recorded.
6) To disseminate preliminary and final results of the project in international conferences, publications, and in a project-oriented internet website.

Ultimo aggiornamento: 04/05/2025