We had 5.4 inches of rain in 4 days, or 33% of median annual rainfall for 1990 to 2016 (which is 31% of the mean annual rainfall for you normals*). Florence went out to see the Sacramento Weir flowing for the first time in her lifetime.
She thought it seemed to be working as designed.
The way it works is when this river gets too high like this, the gates under the railroad tracks are opened (by a guy walking down the tracks using a pole to unlatch each gate) and then the water takes a short cut around Sacramento, rather than through it.
Lots of other people were checking out the weir, too.
* Weather doesn't follow normal distributions, making means a useless measure of central tendency. Normals are people that think that the normal distribution works just fine everywhere rather than being a special case that relies on lots of assumptions. Obviously, median is a better reference point for central tendency, almost always.