Optimus Prime is a large culvert that takes the River Irk underground for it's final stretch before the outfall into the Irwell. I met up with Nckt and Jim Gillette to have a look.
The water level is quite shallow for most of it's length, as a weir holds the deeper water back at the infall. Although shallow the flow is quick and presents a challenge when crossing across the slippery stone floor.
There are a few nice features, the best being an old wooden cattle bridge that despite being in a damp environment was in excellent condition.
Past the bridge the depth increased, so we clung to the sides making it to within a few meters of the outfall.
Going across the outfall is what remains of the Hunts Bank sewer crossing. This bridge used to convey a 3' 6"ft egg shaped sewer across the Irk's mouth and had an open top to allow it to act as an overflow. A storm in September 1896 saw the river level rise substantially higher then the crown of the sewer and allowed water to flood in. After this the open section was closed off and made watertight.