A SuDS Solution from Hydro International has been used to deal with highway degradation and surface water pollution in an environmentally sensitive area of the Scottish Cairngorms.
Poor drainage, flooding and freezing weather had led to a landslip and extreme surface degradation along a section of the narrow A95 that descends on a 10% gradient with tight bends to the picturesque village of Craigellachie on the River Spey, near Elgin.
The solution incorporated Hydro-Brake® Flow Controls within pre-cast concrete weir wall chambers and a Downstream Defender® hydrodynamic vortex separator. Surface water flowing down the steep hillside had been infiltrating the road foundation structure along the 0.9km stretch near Craigellachie.
The water flow had been washing away the aggregate layers and causing a loss of load bearing capacity, leading to premature wear, edge deterioration, and in one location a landslide that resulted in a retaining wall being constructed.
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.
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.