>> Running rainwater into a sewer risks blockages from overloads in storms and material
Yes, that happened at my workplace for a few years. You would get a storm, the manhole covers would lift and the contents run across a public footpath and into a field. Unsuspecting cyclists would go through - the bikes without mud guards would throw a spray up their backs - nice.
The problem was a surface drain running into a sewage system, this had a right angle further down that couldn't cope with the increased flow. The water company has since separated the two pipes and sorted the problem.
I had a look into the manhole covers and an interesting fact is that the flow increases around 8 am, just as the majority are getting ready for work. It isn't just rush hour on the surface you know :)
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