The question is not how long will it take for the theoretical pond to fill nor if it will stay spillway full, but rather will it eventually fill? I think the answer is yes assuming seepage doesn't make up the difference between rainfall & evaporation.
Ed, in a word "No". The bucket will not stay full indefinitely, because rainfall is not predictable in terms of amount and frequency to perfectly offset evaporation. However there is no seepage in a bucket, and if the annual averages are met, there should be just over 1' of water in the bucket by year's end. Our rainfall is spread out pretty well, with a little more in the Spring than other times of year and less in August/September. But most of our evaporation is from May to October. In Winter and Spring, after filling, the bucket may be full and running over after a rain. But the water level may drop considerably in August or September, our driest months, only to fill up again that Winter. Temperature & wind will play a part as well. Is the bucket in sun or shade, what is the air temperature, and is the bucket exposed to wind? Rainfall in inches will be the same no matter how it's measured. But there are several factors that can influence the evaporation rate.
My experience with ponds in this region is the same as Ewest's. In the worst droughts I can remember, water levels didn't drop more than a couple feet in established ponds.
Now I have one more question ...
how many of you have already placed buckets outside to test these theories?
