The Electricity Alliance are in the process of upgrading two number 400kV electricity circuits in order to accommodate new power generation from South Wales. An underground cable route of 2.6km has been identified alongside the existing circuits and has been subject to extensive assessment. The existing circuits shall subsequently be decommissioned upon operation of the new circuits.
The cable route identified necessitates the crossing of the River Wye. The crossing location falls within an Area of Outstanding Natural Beauty (AONB) and the river corridor is designated as a Site of Special Scientific Interest (SSSI) under the Wildlife and Countryside Act 1981. The site is also designated as a Special Area for Conservation (SAC) protected by the Conservation of Habitats and Species Regulation 2010.
The crossing of the River Wye is to be crossed by means of Horizontal Directional Drilling (HDD) and shall be executed from within the floodplain. VolkerInfra were appointed by the Electricity Alliance to undertake the HDD crossing operation. The crossing of the river comprised a total of fourteen number bores in the region of 200 metre lengths, separated by approximately six metre intervals.
The drillings were carried out from within the River Wye floodplain and in a rural area frequented by the public for recreation purposes, as well as a number of species of high environmental value such as otters and water voles. This meant that special consideration was required as far as noise emissions, traffic movements and construction works were concerned to minimise disruption to the local flora and fauna habitat.
Working from within a floodplain also added further complications. As part of the Environmental Agency consent granted to carry out the Horizontal Directional Drilling works, works could only be carried out between the 16th of July and the 14th of October within the floodplain. Outside of this period, the risks of working within the floodplain were concerned too great.
Furthermore, all machinery and plant located within the floodplain had to be mobilised on trailers to ensure that, in the event of a flood and if safe to do so, all equipment could be demobilised to higher ground to prevent pollution of the adjacent river. This meant that constant monitoring of the River Wye water levels were carried out by the VolkerInfra team onsite, as well as indirect communication with the Environmental Agency Flood Warning Department via the client.
Given the challenges which VolkerInfra had to face during the execution of this project, all HDDs were successfully completed in advance of the Environmental Agency's consent cut off date and within specification and budget.