**3. Case studies and discussion**

In the study, risks in dams that are in operation are discussed and risk management of dams in individual and cascade systems is emphasized. For this purpose, some dams on the Upper Euphrates river located in the east of Turkey were examined by considering two separate cascade systems. There are 11 dams on these two separate systems, located on the Murat river and Perisuyu tributaries in the Upper Euphrates. The country's second-largest reservoir (Keban dam), and two dams on the Munzur stream, which is considered a part of the Perisuyu system have also been included to the system considered in the study. Individual and cascade systems of dams were evaluated on the basis of total risks and recommendations were made for risk management. All analyses were carried out depending on the seismo-tectonic models in the regions [42–44]. The projects and their results, which were done previously, have been considered in this study to describe the problem in this study [20, 45, 46].

The first cascade system is located on the Murat river. This system records a total of six separate large dams having heights between 42 and 127 m. The structures located on the main river from downstream to upstream are Beyhan-2, Beyhan-1, Lower Kalekoy, Upper Kaleköy, Alparslan-2, and Alparaslan-2 dams (**Figure 1a**). The total installed power of these dams, which were built mainly for energy production, is 2337 MW and it is planned to produce 5740 GWh of electrical energy annually. In addition, together with some other dam structures on the tributaries, it is envisaged to irrigate an area reaching 120,000 ha. Two large dams located upstream were constructed in embankment type (rock fill and asphaltic core rockfill) and the other four dams were in rigid type (concrete gravity, roller compacted dam). **Figure 1a** shows locations and some basic features of the cascade structure of the dams. The related data about dam characteristics are given in **Table 1**.

The system evaluated in this study and forming the second cascade structure of the basin is located on Perisuyu. These structures, whose heights vary between 34 and 146 m; It consists of Kığı, Özlüce, Pembelik, Seyrantepe, and Tatar dams from upstream to downstream. Two separate dams (Konaktepe and Uzunçayır) on the Munzur stream, which constitutes an important side branch of this system, were also considered as a part of the system. All of these dam structures, except one (Pembelik dam), were planned as fill type (rock fill and earth fill). The total installed power of these dams is 624 MW and they have the potential to produce 1766 GWh of electrical energy annually (**Table 1** and **Figure 1b**).

First of all, seismic hazard analyses were carried out for all dams considered in the study and the seismic parameters that should be taken into account in terms

*Risk Management of Large Dams under Operation Stage and Case Studies for Cascade System DOI: http://dx.doi.org/10.5772/intechopen.113342*

#### **Figure 1.**

*Cascade systems of tributaries of main river of Euphrates basin: (a) Murat river and (b) Peri-Munzur river [8].*

of total risk were determined. On this basis, the hazard rates for the 11 dams taken into consideration are in the "high-very high" range (**Table 3**). Based on the ICOLD method, the risk factor was 36, which is the highest value of the related classificaiton (excluding one dam), and the risk class was determined as between III and IV, and the risk rate was predicted as "high-very high." According to the Bureau method, total risk factor values vary between 143.3 and 229.1, and the Risk Class and Risk Ratio values for all dams are III and "High," respectively (**Table 3**).

The author believes that the risk of dams during the operation stage should be evaluated together with all elements within the cascade system. For this purpose, he introduced a new proposal. The results of this study showed that individual risk definitions of all dams within the two selected cascade systems were formed similarly.


**Table 3.**

*Risk for individual and cascade systems for dams of the basin.*

#### *Risk Management in Construction – Recent Advances*

**8**

*Risk Management of Large Dams under Operation Stage and Case Studies for Cascade System DOI: http://dx.doi.org/10.5772/intechopen.113342*

However, it is seen that the dams in the cascade system do not affect the system at the same impact value in terms of the stability of the system. Within the principles suggested by the author, among six large dams in the cascade system of Murat river, Alparslan-1 dam has and Alparslan-2 have a "high" risk rate while Yukarı Kaleköy dam poses "moderate" risk. Lower Kaleköy, Beyhan-1, and Beyhan-2 dams are represented with "low" and "very low" risk rates.

In the Perisuyu-Munzur cascade system, the risk rates of Kığı and Özlüce dams were found to be "very high" and "high," respectively. Konaktepe, Pembelik, and Seyrantepe dams have a "medium" risk rate, and Uzunçayır and Tatar dams have a "low" risk rate.

Keban dam, which is located downstream of these two cascade systems and has a large storage capacity (31,000 hm3 ), has the location and capacity to compensate for the flooding resulting from all dams upstream. It is necessary to realize a specific program of operation for Keban dam and others located downstream to provide a stable condition for all system upstream.
