No pond here, but I use a similar method for filling a 1000 underground cistern that I use for watering. Amazing how quickly it will fill up (if we ever get rain) - Just as amazing how quickly you can empty it!
Do you also have the front gutters draining into the pond? It looks like from the picture that the pond area is a lot larger than the house footprint, so it will take several inches on the roof for each inch in the pond. Also looks like you will need some Texas sized to replenish that pond!
Good luck do a rain dance
Cheers
John