www.managingwater.co.uk Storm Water Management


providing the required levels of treatment and combining effective flow control with efficient removal of sediments and any hydrocarbon contaminants.”


The basis of the scheme, undertaken by contractor, the Coffey Group, was to excavate and deepen the existing ditches. These were lined with heavy duty polyethylene to prevent seepage into the road structure then filled with carefully graded filter drain aggregate. Flow through the new channels is limited by a series of check dams before eventually discharging into a new pipeline constructed under the road.


The water flow in the pipeline is controlled by a series of three Hydro-Brake® Flow Control devices, located at 300 metre intervals in weir wall concrete chambers under the road. The controlled discharge of the maximum design flow of the Hydro-Brake® units also enables the pipeline to be used as a temporary storage chamber to help mitigate storm events.


road structure which could create icing problems in the winter or the risk of further landslips.”


Under the Water Environment (Controlled Activities)(Scotland) Regulations 2011, the drainage from major roads must be subject to control of any diffuse pollution to help meet the objectives of the EU Water Framework Directive. There were also concerns on the potential of the reconstruction work affecting the water environment, so care was needed to prevent any accidental pollution. Other restrictions, under the General Binding Rule 10 of The Scottish Environment Protection Agency (SEPA), stipulate that any road construction must be drained by a SuDS scheme to ensure flow and pollution control. SEPA Pollution Prevention Guidelines 5 and 8 carefully regulate works which could affect water and look for at least two forms of treatment to the surface water runoff.


“The road is cut very tightly into the hillside, which limits the construction space along much of the stretch of road although there is a small lay-by set into the hillside around the middle of the scheme. There are also a minor road and farm entrance which complicate the road drainage solutions,” Darren continues.


An existing short retaining wall and a series of ditches were proving inadequate, especially as rainfall intensity is increasing with climate change. Simply improving the ditch volume and water retention with a conventional approach such as cast concrete channels was not an option due to space within the highway boundary. Also, the lack of flow control would risk additional sediment being washed into the river.


“Because of the gradients, surface area and other site characteristics, the volume calculations were complex. Hydro was able to design a minimal maintenance SuDS solution


The last of the three Hydro-Brake® units is located at the downslope end of the pipeline, in front of the Hydro Downstream Defender®. This device ensures high sediment retention even during storm events, with no re- entrainment, while controlling floatables and providing hydrocarbon separation. The Downstream Defender® discharges over a reinforced rip rap face set into the embankment to control erosion, and then to the river.


“The result is an elegant solution which meets both the environmental concerns and the serious structural problem.” states Darren. “As the purity of water in the catchment is very important, and the safety of the infrastructure is greatly improved, we have achieved a good result.”


Client: BEAR for Transport Scotland Main Contractor: the Coffey Group


For more information about Hydro’s Stormwater management products please call 01275 337977, email enquiries@hydro-int.com or visit www.hydro-int.com.


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