In your world, a river would be flowing at a speed of 132 m/s (= 295 mph) after coming from 3000 ft [1]. Now compare this to rivers in the real world and you wi

In your world, a river would be flowing at a speed of 132 m/s (= 295 mph) after coming from 3000 ft [1]. Now compare this to rivers in the real world and you will see that you're overlooking a factor which reduces the speed of the flow by two orders of magnitude. [1] Potential energy of 1 kg water at 3000 ft: 1 kg * 900 m * 9.81 m/s² = 8829 J. Kinetic energy: 8829 J = 0.5 * 1 kg * v² ==> v = 132.88 m/s