Investigating the possibility of cavitation and scouring of the stilling basin in the spillway of the Sahand earth dam using Flow-3D software

Spillways are one of the important hydraulic structures of a dam, which perform their duties during floods in order to maintain the health of the dam. In this research, the free ogee spillway of Sahand dam is analyzed with Flow-3D modeling software and the effective hydraulic parameters on the performance of this structure including the occurrence of cavitation and scouring of the stilling basin have studied and verified with lab model. The results show that cavitation occurs in three areas along the service spillway of Sahand Dam. The ogee crest part of the spillway, the part that slope changes in the middle of the chute and the flip bucket are the parts that have the problem of cavitation. For the ogee crest part, the tip curve should be modified and the cavitation-prone part should be made longer to create a vacuum and eliminate the possibility of cavitation. If this doesn't work, aeration should be done. In the middle of the chute, aeration should be used by creating a gap in the floor. Also, the end edge of the flip bucket should not be smooth and reshaped as a curved surface. The scouring depth for the flip bucket of the Sahand dam spillway is about 7.6 meters, and to deal with it, it is necessary to organize the downstream of the spillway using a excavated pool, protection and a stone riprap.