Water current speed?

Question

when rafting the normal speed is at a speed of 7.3 mph. When we hit the rapids, speed will triple. How fast will we go in the rapids?

Answer 1

Dont you need 1.21 Giggawatts to reach speeds like that?

Answer 2

3 times 7.3 is 21.9, but that is way faster than a raft travels. Speeds of rapids may reach 10 or 12, paddleing it is about 3.