South Lanarkshire College is moving from three separate campuses to one purpose built site on the Scottish Enterprise Technology Park in East Kilbride. Attenuation of storm water runoff from the new building to meet discharge limits and quality requirements is being achieved with significant cost and space savings by installing a storm water control system from Hydro International, complete with a Downstream Defender® hydrodynamic vortex separator.

Engineer Brian Miller of consultants Charles Scott & Partners explains: "The site is on a slope, and the buildings are surrounded by a car park on two levels. Half the building roof and upper car park runoff are directed through porous pavement and piped to a filter drain and perforated pipe to a Hydro-Brake® Flow Control device.

“The lower car park and the other half of the roof are directed straight to the filter drain, perforated pipe and Hydro-Brake® Flow Control. This then directs the flow to a Downstream Defender®, which removes most of the sediment plus floatables and hydrocarbons, prior to discharge.

“As well as the system meeting a discharge limit set at 5 litres/sec, the combination of Downstream Defender® and porous pavement meets the requirements of the Controlled Activities Regulations (CAR) under the Water Environment (Controlled Activities) (Scotland) Regulations 2005.

“During storm events excess flow is attenuated by the Hydro-Brake® Flow Control, so the back up fills the attenuation tank via the perforated pipe. The tank comprises nearly 700m3 of Hydro’s Stormcell® modular storage units, which were benched into the slope, and the lower car park constructed over the top. Stormcell® is load bearing, so civils structural work was minimised. The installation saved space in being sited under the car park as well as time in being part of the car park construction rather than a separate event.”

Hydro’s Downstream Defender® is designed to provide effective silt and sediment separation at all levels of flow up to its designed maximum, with no power requirements and minimal maintenance limited to sump emptying. It is thus ideal for dealing with first flush and fluctuating flows occurring in high rainfall areas, as the quality of discharge is not compromised by storm flows.

Email: nicola.poyser@iassmarts.com