Temporary construction site drainage - Need advice/ideas

[TheRobster]

Hi all,

I'm currently designing the surface water drainage for a new school building in West Yorkshire (UK). The main issue with this project s that there is already an existing school on the site and the company I am working for intend to build the new school at the same time as the old school is still there (on a different part of the site obviously) and then when the new school is up and running, demolish the old school. It will take approx. 9 months to demolish the old school however as there is a lot of asbestos is the building so they have to take a lot of precautions when demolishing it, hence the long time period.

So.....the main problem I have is that the local water authority (Yorkshire Water) won't let us discharge water into their combined sewer system at a rate greater than the existing building. If both the old and new buildings are existing at the same time, then this will obviously increase the overall rate of runoff from the site. I can design a SUDS (sustainable urban drainage system) for the new school to attenuate the flow from that no problem, but I'm not too sure what to do about drainage from the old scool whilst it's been demolished.

My client does not want to build any permanent storage structures (e.g. underground tanks) to attenuate flow from the old building whilst it's being demolished as they see this as a waste of money. They have suggested just having above-ground tanks located around the site and essentially plugging the drainage from the old school into these and letting it drain out of the tanks slowly.

I don't like this idea though. What happens when the builders start removing the drainage components from the old school? How are we supposed to stay connected to the tanks then?

They have also suggested using the new car park as a temporary storage area. The problem I see with this though is that every single time it rains, the car park will flood. I don't see this been acceptable to the building owners to be honest, nor do I believe it will be safe to be driving cars through a small lake every time it rains!

Anyway, does anyone have any advice or ideas on a suitable temporary drainage set-up for the old school whilst it is been demolished? We almost certainly will have to provide some attenuation as well....I was thinking some kind of temporary lagoon might be the best solution, unless anyone has any better ideas?

Thanks
-Richard

*Edit*

Any information/advice on any sort of temporary construction site drainage would also be welcome. This is the first project I've worked on where we have an existing building to think about......all my other projects were greenfield developments so there weren't any issues like this. Does anyone have any links to websites that cover the basics of temporary site drainage, as I don't seem to be having much luck Googling for information at the moment.

[Tony McC]

It's probably too late now (I've been otherwise distracted by family matters) but I reckon you have no choice but to create a temporary attenuation system for both the old and new schools. It will give the new building significant over-capacity, once the old building is gone, but if you do a costing, I reckon it wouldn't be a huge amount more.