Auchenrivock, Canonbie, DG14 0XF
Dumfries and Galloway Council
With a poor accident record, the initial project on the 2.3 km upgrade of the A7 Auchenrivock route, south of Langholm was to improve and increase the number of overtaking opportunities of the roadway, while incorporating the need of cyclists and pedestrians, the water management needs of the scheme, including surface water runoff had to be taken into consideration.
A treatment solution for the surface water runoff was required but there was no nearby space for SuDS ponds. The £8 million project originally involved the design of three SuDS ponds to minimise the risk of flooding and treat pollutants and sediments in a sensitive rural location, however after identifying the topography of the project, other solutions were looked for.
Minimising the environmental impact of the project was a key consideration for the council and Transport Scotland and a SuDS compliant drainage solution was one of a range of strict environmental requirements, including measures to facilitate the movement of fish and mammals, preserve habitats and provide sympathetic landscaping.
After looking at several options, the advanced vortex separator, the Downstream Defender® was chosen and installed to provide pollutant and sediment removal in a very small footprint compared to a SuDS pond and the treated surface water discharging into the River Esk.
As part of the project, the original road is to be de-trunked and part of it converted into a cycle path.
Resident Engineer, James McLeod of Dumfries and Galloway Council’s in-house Design Function DGDesign said “The new single carriageway was constructed in hilly terrain to the west of the original road and the only level ground available for a SuDS ponds was some distance away. To construct a third pond would have meant building a new 300m length of sewer and required major sewer works to be carried out during the road construction phase, with a potential consequent road closure”.
“It was identified that a Marshalls’ Downstream Defender® made in conjunction with Hydro International, could provide a space-saving solution, which achieved the required level of pollutants and sediments removal before discharging stormwater into the nearby River Esk. The remaining two ponds were redesigned to accommodate the additional stormwater storage capacity.”
For more information on our precast Downstream Defender® please visit www.marshalls.co.uk/commercial/product/downstream-defenders