Page - 926 - in Book of Full Papers - Symposium Hydro Engineering

Urkmez dam is a earthfill dam on Urkmez River near Seferihisar County. It has a 32.0 m height from river bed. When the reservoir is at maximum capacity, the facility impounds 7.92 hm3 of water with a reservoir surface area of 0.61 km2. Its construction was finished in 1991. It was designed to provide water for irrigation of 370 ha and drinking water with annual capacity of 0.78 hm3. The crest length is 428 m and the side slopes of main embankment is 3.0H:1V for upstream and 2.5H:1V for downstream (H=horizontal and V=vertical). On the section there is a central impervious core, which is composed of compacted impervious clay and a transition section of sandy and gravelly aggregates was designed between the core and pervious coarse grained soils. The alluvium under clayey impervious core, which is composed of different size of river bed material, was removed before beginning the construction of the main embankment According to the seismic hazard analyses of this study, it will be subjected to a peak ground acceleration of 0.310 g by an earthquake of 5.7 magnitude and its embankment is 1.7 km far away from an active fault given in the updated seismo-tectonic map of Turkey. Its TRF value is 188.5, and it is identified as risk class of III. This 37-year old earthfill embankment is in excellent condition, but it cannot meet current seismic design standards. It will be under near-field motion during earthquake. Therefore, its seismic upgrade should be provided soon. 5. CONCLUSIONS For the large dams within the Izmir Metropolitan Area, the seismic hazard rating of the dam site and the risk rating of the complete structures were determined and possible modes of failure were estimated. This paper summarizes the seismic hazard and total risk analyses of six large dams, which are located on two basins in Turkey, as based on a preliminary study. The study identified that five of them are under near source effect. As a result of this study, 83.3 percent of dams has extremely high of risk class while others are classified in high risk class. Therefore, detail seismic hazard analyses should be performed for these structures as based on the updated seismic data and design code under circumstances of the study of a national safety program for dam. In other words, these dams must be re-analyzed by selecting appropriate seismic parameters. Rehabilitation design and construction measures, if necessary, may follow after in cases where the dams are found deficient seismically. REFERENCES 1. Fraser, WA and Howard, JK (2002). Guidelines for Use of the Consequence-Hazard matrix and Selection of Ground Motion Parameters: Technical Publication, Department of Water Resources, Division of Safety of Dams. 2. Jiminez, MJ, Giardini, D and Grünthal, G (2001). Unified Seismic Hazard Modelling throughout the Mediterranean Region. Bolettino di Geofisica 926