Beavers need about three feet water around the lodge in order to be safe against predators, survive freezing, and to be able to cache enough food to survive the winter. It seems obvious that even if the beavers repaired the dam immediately, there is little or no chance of that happening before winter. I suspect the beavers knew that long before I did, because there seems to be no further efforts to seal the breach. They have either moved on, or retreated to an unused lodge in the upper pond.
However, that hasn't stopped the activity of the beavers in the upper pond. They do not like to flow of water through the culvert after a rain and were working to try to breach the cages. Their persistence and ingenuity never cease to amaze me. They managed to burrow under the culvert cage enough to get their teeth into the culvert pipe, chew it away and make their way into the culvert. Then mouthful, by mouthful, they dragged pond grass and mud all the way through to begin damming the other side.
Because of the tight fit, they are not able to get any sticks inside the culvert and the work they have done so far will be washed away with coming rains, as long as I prevent further excursions into the culvert.
UPDATE 6-27-18 - A picture is worth a thousand words, so here's a thousand word update on what I have done to stop further culvert clogs.
I suspect that if they do get through this, we have Arnold Schwartzenbeaver living on our pond.