You're missing a key variable here: time. If you dumped that amount of rain water in one second, you'd have a Tsunami. Dump it over a 24 hour period, it might

You're missing a key variable here: time. If you dumped that amount of rain water in one second, you'd have a Tsunami. Dump it over a 24 hour period, it might flow out smoothly out of a little stream. Dump it 10% in an hour, 50% in the next hour, 10% the next hour, 30% over the next 12? Um, that's harder.