Surface water attenuation - What is it

[bobmitch]

I cleared a blocked surface water drain at a NHS centre and found between two manholes what looked like black plastic accross the entire diameter of the drain. The plastic has cuts in it which obviously allow water through. At first i thought it had been capped off during the recent building work and forgotten, but i now think it may be some sort of attenuation system. The next MH downstream has a reducing tunnel through it which allows water through during normal rainfall but also allows water to flow over the tunnel during heavy flows. The final MH on their property as a weir type affair.

The site is in a big medical complex and I didn't notice any nearby water courses that the flow may need reducing for before joing it.

Any help?? ???

[andpartington]

did it seem to be a thing of purpose or just a grate that some dick lobed in

andy

[bobmitch]

no as definatley been put in to serve a purpose, the pipe diameter is about 2 foot. the plastic is perferated throughout to allow water through.

[Suggers]

Flow in Flow-Joe

[Tony McC]

Is it a debris trap?

[flowjoe]

Nope, not seen that one

The systems normally comprise of a large diameter pipe system with a small regulated outlet, usually blocked with a large piece of shuttering left over from a manhole construction

But that was last week and progress is so bloody quick i am struggling to keep up, thank god water still flows downhill, unless you are in yorkshire that is

[seanandruby]

dont s'pose you got photos. its good to log anything unusual. how thick was it, was the cuts machined, or, hand made.? have used simular stuff on land fill sites that are being built on for odour control.