Just spotted it… It’s part of the water filtration for the tiger ponds.
Water is collected from the roof and stored underground in a tank holding over 200,000 ltrs. It is then used to keep the small pond (20Mx5M) next to the Elephants topped up; this pond is open the sunlight and has fish in it to maintain a good chemical balance. The water is then pumped from there into the two tiger ponds and is allowed to fall about 2M to increase aeration (and for fun) from there it runs via a small streams and some pipework into the thing you have a photo of; It has steps and is full of small baskets of filtration material to remove any large partials before it is re-introduced into the pond.
Thanks for the response bazthezoobuilder,my best guess would have been some sort of filtration system.From what you have just described it sounds a very well thought out system as well!!
Well thank you I’m glad to say it was one of mine.
(Don’t tell anybody but I am still having some problems getting the overflow to work at the right level)
