I wasn't expecting much from this little culvert, both infall and outfall had large grills, with about 340m of double concrete box section stretching between. Not far from the outfall a large low concrete bridge crossed and deep sinking mud prevented easy access beneath. To one side of the bridge was a window, I climbed up and found myself in an access corridor.
At one end daylight poured in through a padlocked gate, the other direction had a ladder. This went up to a small chamber and another lead downwards into a CSO chamber.
The sewer was carried in a large concrete topped channel with a slot in the side for the overflow. It traveled from the RBP (Round brick pipe) pictured, through the overflow chamber and into a smaller RBP. This must curve round and travel across the bridge, under the access passage mentioned earlier. Any spills leave the chamber through a series of slots which stepped down into the culvert. The bridge can be made out in the background:
The rest of the shortish journey to the infall was through concrete box. What looked like an equipment access chamber was the last thing of interest before the bars of the infall.