April 17th – The minutiae of drainage engineering are wonderful. I’ve been passing this array of manholes for a couple of weeks now, and noticed that new bars had been installed across the covers. It’s taken me ages to work out what they’re for. It’s not what one may imagine.
Opposite a small, automatic sewer pumping station on Green Lane at Bullings Heath, Walsall Wood, there is the concrete cap to what must be a storm buffer. A storm buffer is a large underground tank that, in time of heavy rainfall, collects drainage water and fills up, storing it and allowing slower discharge into the main network to prevent overload. There are lots around and they work well; you can tell this is one due to the large circular ‘cap’ evident with the access covers.
Recently, bars were mounted over the covers. Initially, I assumed they were to prevent access by drainers – a type of Urban Explorer that goes into sewers and storm drains to explore – but they aren’t actually secure. They’re secured with normal nuts and bolts, not locks. A couple of covers in front (not shown), which I think house pumps of valves – are not so protected.
They have actually been fitted to prevent internal pressure from blowing the access covers out. If the buffer filled to capacity due to a storm event, water pressure would increase against the hatches, and lift them out. That would then expose anyone walking through the subsequent flood liable to fall into a very deep, open manhole.
The bars are therefore a safety feature.
I wonder what has occurred, and where, to make this risk suddenly appreciated?