Hi Keithb, yes that is a small bridge that crossed a feeder stream that drained into the Mersey by Kingsway bridge,
I used to walk over it on way to school at Richard Fairclough's, it had a slewce gate underneath and sometimes the water running over the gate made a squealing noise we kids used to say it was a pig stuck in there we used to hold a kids ankle so he could lean over the edge to have a look, Dam dangerous but kids will be kids, sorry I have to report, no pig ever found.