Well, it's kind of a year old. The first inundated panic driven hole in the ground was dug in December 2015. It was taking shape early last January. And it was assuming it's current shape before the end of that month.
During a lot of the intervening year, the levels have been much lower. 48 hours of steady rain will fill it. But from full, it takes about 2 weeks of drought to drain - but even after that there'll be wet sediment in each of the 3 main ponds. That happened once all year, back in May. Most of the time, the 3 ponds are spearate, each of them maybe 1ft deep. There's a 4th, very small, pond at the SE end, (top left corner in photo.
In the photo above the water is as high as it's been since last winter. It gets no higher than this, because of the overflow into the Council drain, (at the red marker in the very forefront of the photo) is set to this level. I'm curious to see how it's flora will do next Spring when the level drops again.
For example, in the middle pond there's a dock growing at such a level in the bank that its foliage would be inundated frequently, but not for more than a few days. It's roots must have been below the water level most of the time. Now, it's completely submerged, and will likely remain so most of the Winter. Ditto clover and grasses.
This is a (very) rough sketch of the pond in section, (L to R = N to S), where the darker blue is the summer level, and pale blue winter. I have thought about excavating it evenly, taking the time to puddle the clay, so that it doesn't almost dry out in the Spring, (when it's liable to have frogspawn, though there was none this year).
But then, so far it seems to be doing its day job - keeping the beds from water-logging - very well. And it's only a year. So I'm going to leave it to its own devices for now. I've sprinkled on some pond margin plant seeds - 99p on eBay, no idea what they were. There's also the typha latifolia, and I'm hoping that will do well next year.