Officially known as the North Eastern Storm Relief this drain stretches for over 8km and is the overflow for several large sewers.

This culvert outfalls to the River Croal via two 4ft RCPs and carries a small watercourse under Bolton.

The Barley brook comes from a 3ft RCP and enters the open briefly before the infall to the culvert proper. The tunnel starts off as a 6ft stone arch, it passes under a railway line then shrinks to 5ft Brick.

This little culvert in Middleton is a baby at 20m in length, once inside it opens to standing height.

This culvert takes the River Roch around 450m under the middle of Rochdale.

Getting in couldn't have been easier, a hinged lid in some bushes dropped us straight into the chamber. It was a simple concrete setup, the weir had no screen, the designers choosing a grill over the dual outfall pipes instead.

ML's Upper Limits is a cluster of CSOs that drop into the mighty Motherload (NSWI) deep in the bowels of Bristol.