Civil engineering question

If you ask an engineer to design a drainage system for a huge concrete area , say an airport, and you give him the once in a  hundred year rainfall figures to work with he will come up with a suitable system to cope with that. If you then drop the once in a two hundred years storm on it then it will flood.It's not a man made problem It's just that the weather is becoming more unpredictable. We can design to cope with anything imaginable but when the unimaginable  ( or the unaffordable ) happens we are buggered.

I have commented on a number of planning applications that have included a drainage design that "will cope with a 1 in 100 year event" .......usually they incorporate attenuation systems.

When you delve further into the design, you find that they have ignored surface run off, blockages in pipework, run off from outside the site itself......etc.

They assume that they can discharge into a local watercourse......one that is already flooding by then.

They assume that they can store excess water on paved areas.....i.e. that they can cause deliberate (but supposedly controlled) flooding on the site.

In other words......they design something that simply doesn't work. But it bamboozles the planners sufficiently (and ticks the box that says that they must design a system that deals with flooding) so they get approval.

And then the new buildings flood.......and so do the unfortunate residents of adjacent buildings. Who can then no longer get insurance for their buildings. And we see yet more unfortunate scenes on the news.......and hope that it never happens to us.

Well we have those who have designed systems and those who have commented on them. It's still hissing down in Montenegro and I hope the designers won here

The engineer will design the system for the 1 in a 100 year event, and probably build in a good bit of leeway - like 100%!

Then the accountants arrive. Need I say more.

As long as planners continue to give permission for houses to be built on flood plains there not a lot people can do except refuse to live there! If no one bought them, they wouldn't get built!! 

The trouble is that housing demand is such that beggars can't be choosers.

The engineer will design the system for the 1 in a 100 year event,

....and few people buying a new house expect to be there for 100 years.........

The trouble is that housing demand is such that beggars can't be choosers.

There is no housing shortage around us (or much of the north of England) but still we get these unpopular estates foisted upon us.

The engineer will design the system for the 1 in a 100 year event,

....and few people buying a new house expect to be there for 100 years.........

There is a common misconception that a '1 in 100 year flood event' will only happen once in a 100 years.

The reality is that it's an event that has a 1% chance of happening in any year.

We had several of them within a couple of years not that long ago.

We have watched the local river overflow and surge across adjacent fields many times (fields that are now full of houses). The Environment Agency were in denial and said that the river 'never breaks its banks' despite eye witnesses, photos and video footage proving the contrary.

Sadly, our friends who live in York, did all the things they were advised, but their house flooded anyway when water came up through the ground, into the foundations and then up through the floorboards.

Fortunately, because they'd done what they were advised by their insurers, they could claim.

They've now taken the first piece of advice in this thread - moved!