The private pilot reported that he was flying the helicopter about 500 feet above the ground and decided to descend to follow a riverbed. While descending to the river, one of the passengers alerted him to the presence of power line wires that obstructed their flight path. The pilot applied full aft cyclic and collective in an attempt to avoid colliding with the wires; however, the tail boom and tail rotor contacted the wires. The impact resulted in the separation of the tail rotor blades and the bottom section of the vertical stabilizer from the helicopter. Following the collision the pilot initiated an autorotation. Upon touchdown, the helicopter bounced and when it touched down again, it was moving sideways to the left and rolled over. The helicopter came to rest on the bank of the river on its left side. Examination of the helicopter revealed substantial damage to the main rotor assembly, the tail rotor assembly, vertical stabilizer, tail boom, and fuselage. The pilot reported that there were no mechanical anomalies with the helicopter prior to the accident.