Risk Assessment for Spillway Overflow Structure Components (Case Study: Chandir Dam)

In this research to investigate the flood risk over the Chandir spillway, located in the North Khorasan province, the acceptable distribution of risk for the spillway components and its consequences on the hydraulic performance were studied. For this purpose, the spillway was designed for discharges with a return period of 100 and 1000 years. The 3D flow field for the designed structure was investigated in the event of flooding with a return period of 100 and 1000 years using the FLOW3D software. The results show that in the event of a flood with a 1000-year return period, whilst the structure has been designed based on a discharge with a 100-year return period, flow separation and an increase in the local shear stress occurs in the stilling basin. Moreover, the risk assessment results show that the stilling basin length plays an important role in flow energy dissipation however, increasing the stilling basin length more than 20 meters would not decrease the dissipation rate. Also, the length of the stilling basin influences the amount of the secondary depth, and the reducing of the basin length to less than 15 meters will prevent the formation of a hydraulic jump even for a discharge with a return period of 100 years. Finally, the risk assessment shows that by accepting the risk amount of 13.56 %, it is possible to reduce the length of the stilling basin to 20 meters.