The River Irk travels under Middleton town centre for around 500m in a couple of parallel concrete box culverts.
The culverts are pretty much mirrored but do not connect together internally, one was a trickle and the other a torrent.
Walking up the left hand branch, sand and the odd brick gave way to a flat floor with only an inch or two of water. A few small side pipes joined in and a couple of slightly larger ones. I must be getting old as couldn't be bothered to see where they went.
At the infall it became apparent that a few trunks had formed a dam were shunting pretty much all the flow into one side.