5 billion gallons / 9350 km² is just 2mm. If that fell in one hour, the flow into the lake would be 5200 m³/s, except it would be lower since it takes time for the water to reach the lake.
The normal flow of the spillway is 4200 m³/s.
Have I done something wrong here, or missed something obvious? 2mm/hr is a pretty moderate rain.
Not all the water (normally!) makes it to the lake, and the average rain over time is probably less than that. Otherwise, no, the math looks fine, but this is why the reservoir is useful as a flood-control system. It can take the fairly large flow caused by even moderate rain, and spread it out over time.
Things get iffy once you have heavy rain for long enough that the soil saturates.
5 billion gallons / 9350 km² is just 2mm. If that fell in one hour, the flow into the lake would be 5200 m³/s, except it would be lower since it takes time for the water to reach the lake.
The normal flow of the spillway is 4200 m³/s.
Have I done something wrong here, or missed something obvious? 2mm/hr is a pretty moderate rain.
[1] https://en.wikipedia.org/wiki/Lake_Oroville