VHE Construction ‘Pearls in Peril’ project submitted for prestigious award

The 2016 Saltire Civil Engineering Awards are awarded by the Saltire Society and the Institution of Civil Engineers Scotland. The awards are in recognition of excellence and innovation in civil engineering. The works, undertaken on behalf of Scottish National Heritage, have been submitted in the Environmental category.

The freshwater pearl mussel is declining dramatically throughout its range and is under grave threat within Great Britain. The River South Esk is designated as a Special Area of Conservation (SAC) with internationally important populations of freshwater pearl mussel and Atlantic salmon.

‘Pearls in Peril’ (PiP), a UK-wide project to safeguard the future of the freshwater pearl mussel, funded the restoration works. Activities were licenced to protect otters and water voles and under close scrutiny to minimise silt disturbance to protect fish and fresh water mussels. There was a small area of SSSI (Archaeological interest) which VHE protected with track mats to allow transfer of materials and construction plant.

The £0.15 million restoration works comprised the removal of large rock-armour boulders, that were installed over twenty years ago, and regrading of the river embankments to a natural profile. This allows the river to naturally erode the banks and create adequate levels of silt both in the river and on the river bed to sustain the mussels and spawning salmon.

The original rock-armour had been so effective, that the silt levels on the bed of the river were almost non-existant – certainly not deep enough to sustain the mussels and salmonids. In addition to the removal of the rock-armour and embankment regrading, four sections of Paleochannel were graded out to provide rest-up ponds for the salmon migrating upstream, to the spawning beds.

Working on restoring the original riverbanks, on the edge of the Balmoral Estate, VHE overcame a number of logistical challenges. In order to access some of the remotely located areas of works, three 10m Bailey bridge structures were mobilised and erected over existing bridges. This increased the bridge capacity to 28 tonnes, allowing the construction plant to cross up to the Moulzie Glen.

Due to the environmental considerations and remote location extreme care was taken throughout every aspect of the project. As the projects were located in ecologically sensitive areas a number of precautions were taken to ensure that there was no damage to the natural environment including the use of ‘Low Ground Pressure’ plant to minimize damage to the surface soils.

Works were carried out on programme with absolute minimal disruption to the surrounding National Park, which was busy with summer season ramblers, as well as livestock. Ground Guards were used to protect the plant-life and provide a safer working surface.

The site team worked well with the Designers and local landowners to adjust designs locally to suit all parties and minimise the impact of the farmland and local environment, and where possible use local resources to carry out the works under close supervision of the VHE Team. A sustainable environment has now been created to ensure the long term success of breeding stocks of pearl mussels within the river and bring benefits to the whole river ecosystem while preserving the existing beauty of the area.