Hi Theo - answers below:

a) It dropped a foot in 2 weeks after some hard rains

b) It is app only 40% full - has never gotten higher than that. After a hard rain - we can see it rise anywhere from 6-18" above it's current 'holding height' and it gradually gives it all back - and that translates to app 1" per day AFTER a hard rain.

c) The bottom of the pond has 2' or more - the walls taper up from there to app 8"-18" depending on which side. (shallow side closer to 8" - dam side 18")