فهرست مطالب مینا سیفی زاده

Storage dams are constructed for several aims such as; water supply, flood control and energy generation. Dams are being threat by breakage and cause severe financial and human losses in downstream. If dam breakage phenomenon and its resulted effects are furcated before dam construction, the losses will be reduced in the future. In this study, the Polrood dam breakage due to overtopping has been investigated by BREACH GUI model. Results showed that the flood hydrograph due to dam breakage possessed a discharge peak of 47253 m3/s. This peak occurs 27 hrs after flood beginning an hour after overtopping.Then, flood routing was carried out in order to determine the effects of dam breakage by HEC-RAS model. The results of flood routing showed that the discharge peak arrived at the last cross section of 15 km distances in the dam downstream after 54 minute which possessed a decrease of 62%. The overlay of floodplain maps with Google Earth model showed that 18 villages and some regions of Kelachay and Rahim-Abad cities are affected by flooding in dam downstream. The flood resulted of this dam breakage, also causes river erosion near to the dam.

With construction of storage dams، a large amount of sediments are accumulated behind them. Therefore، water released from the dam is so clear and possesses high sediment transport capacity، which causes the river erosion at downstream the dam. In this research، Polerood river morphological variations predicted in downstream of dam using mathematical models for a short period post dam construction. Then، results were compared with lack of dam existence manner. Results showed that، the presence of the dam causes more erosion in the river. Maximum erosion in presence and lack of the dam were 4. 7 and 3. 7 m، respectively. The maximum influence of the dam construction on river morphology is up to 10 km downstream from the dam axis. At far distances، river bed variations in both the presence and lack of the dam were the same and the intensity of these variations was very low. The most river variations occurred at early years and variations intensity reduced gradually. Results also showed that erosion and sedimentation in the river is balanced by the time and river will be arrived at a regime case.