Onshore cable route
From landfall at Brooklands Pleasure Park, almost 27 kilometres of buried onshore cable transports the power produced at Rampion to a new onshore substation in Twineham, Mid Sussex.
A decision was made at the start of the project to bury all the cable and avoid the use of pylons. The cable has been laid in two circuits and the cable route itself was designed to take account of ecologically sensitive areas, with construction methods tailored to reduce impacts. One was at Tottington Mount where sensitive chalk grassland required the use of a special trenching machine along with a turfing machine to remove and replace the turf grass.
Construction of the onshore elements of the project began in autumn 2015 with ABB carrying out civil and enabling works at the substation site and cable route works being undertaken by contractor Carillion. To help manage the onshore construction the cable route installation was divided into 12 stages, starting with the substation at stage 1 and moving broadly from south at the coast to north at the substation. The completion of each stage depended on ecological and consenting restrictions as well as general weather and ground conditions along the route.
A particularly sensitive section at Tottington Mount in the South Downs National Park required specialist trenching and turfing machines to deal with the steep gradient and thin topsoil covering the distinctive chalk grassland. Monitoring of the reinstatement of the grassland will continue, with seeds harvested from the area being kept in the Royal Kew Gardens seed bank and available for use if required.
A technique called horizontal directional drilling was used at four landmarks along the cable route– under the A27, River Adur, railway line and the A259 and Lancing Beach. By drilling under each of these, traffic and trains were not interrupted and the beach could remain open.
In terms of the onshore cables, there are two circuits, each with three cores. Each individual core is approximately 10cm in diameter and laid in a trefoil (triangular shape) formation with two on the bottom and one on the top. Two fibre optic cables are laid either side on the power cores. The cables are buried at approximately 1.6m deep and the minimum depth of cable cover – the distance from the top of the cable to the top of the surface of the soil – is 1.2m.
There will an on-going 10 year monitoring programme to ensure the reinstatement of the full cable route.