Scores of firms in the Lower Don Valley are at work as normal despite waters last night almost reaching the same level as June 25 12 years ago.
Walls, barriers and 600 one-way valves on drains were installed in the aftermath of the disaster, and rivers were cleared of logs, branches and rubbish which had lodged under bridges and blocked channels.
Sheffield Chamber chief Richard Wright said the fact that it was business as usual today showed the defences had worked, despite rivers levels being “equivalent” to 2007.
He added: “The £20m paid for itself last night. I’m really pleased. Business can have the confidence to continue to invest in the valley now.”
In 2007, scores of companies near the Don were flooded, from the city centre to Meadowhall, with some people rescued by helicopter.
Steel firms Forgemasters and Firth Rixson (now Arconic) were inundated, severely disrupting operations for weeks. Flooded companies lost customers and insurance claims ran into the tens of millions.
Mr Wright added: “Can you imagine if it had happened again? There would be not just the economic impact but the long term reputational impact too, with people moving out and not investing.”
The £20m defences were part-funded with £2m from local firms. They were built to a one-in-100 year likelihood of a repeat of the 2007 floods - with a margin on top to allow for the predicted impact of global warming, Mr Wright added.
Some 90 per cent of firms signed up to a flood alert system and were able to respond to warnings yesterday, moving critical equipment and people out of harm's way, although it wasn’t necessary in the end.
Meadowhall spent £2m on its own defences, it also paid into the wider flood fund.
A spokeswoman said the defences worked and the centre remained dry and secure.