Page - 922 - in Book of Full Papers - Symposium Hydro Engineering

Table 3. Selection of Design Earthquake as based on risk classification [13] Hazard Analysis Deterministic Method Probabilistic Method Class Hazard Ratio I Low 50 % TR = 224 years (*) II Moderate 50 % TR = 475 years III High 84 % TR = 975 years IV Very high 84 % TR = 2475 years (*) Tr = Return time The seismic hazard analyses were performed for six dams throughout this study. The results with total risk of each dam are given table 4. All dams with exception of Alacatı Kutlu Aktas dam are identified in class of IV with extremely high hazard rating. One dam site have moderate hazard rating and are identified as hazard class of II. ICOLD [10] state that if the PGA value is greater than 0.25 g and the energy source is closer than 10 km from the dam site, it is classified as hazard class IV with hazard rating of extreme. For eleven dams, the distance from dam site to active faults, which are given on updated seismic maps, ranges from 1.1 km to 3.1 km. The large dams of basins, which are under the influence of the near-field motion, have been constructed to very close to active segments of the horst-graben fault system in west Anatolia, which were determined after 2013. Table 4. Total risk of dams considered for this study. No Dam Hazard Analysis Total Risk (ICOLD,1989) Total Risk (Bureau, 2003) Class Hazard Ratio Risk factor Risk class Risk ratio Risk factor Risk class Risk ratio 1 A.K. Aktaş II Moderate 30 III High 163.4 III High 2 Balcova IV Very high 34 IV Very high 187.6 III High 3 Gordes IV Very high 36 IV Very high 155.6 III High 4 Guzelhisar IV Very high 36 IV Very high 158.3 III High 5 Tahtali IV Very high 36 IV Very high 186.6 III High 6 Urkmez IV Very high 32 IV Very high 188.5 III High Throughout this study, two methods have been considered to quantify the total risk for dam structures. In DSI guidelines, total risk factor depends to reservoir capacity, height, evacuation requirement and potential hazard (DSİ, 2012). According to DSI Guidelines all dams are categorized in III and IV risk classes with high and very high risk rating. Following Bureau's method, all large dams are classified in risk class III, a high-risk rating. In Bureau method, the values of the TRF range from 96.5 to 208.6. This means that there is no dam having a risk classes of I and II for all dams considered for this study. Author thinks that the solution obtained from Bureau method is more rational than that of the DSI guidelines. 922