This project involved the construction of a new flood defence bund across Chivenor airfield, North Devon. A design for the project had been carried out based on an existing site survey, but there were no ground control points on the site suitable for the contractor to set out the works.
Preston Engineering Survey Ltd were asked by the client to install 12 no. survey stations to Ordnance Survey national grid and level datum across the airfield. Using 3 static GPS receivers a triangular survey network was created that could then be post processed and adjusted for accuracy. Overall positioning of the survey was achieved by tying the stations back to the Ordnance Survey active station at Appledore. Further checks were carried out by surveying existing structures in order to verify that the new survey control related correctly to the existing survey data.
Level control in flood defence work is critical, so the new survey stations were checked using a traditional precise optical level to verify the GPS derived heights. A level check was also carried out against the nearest Ordnance Survey benchmark on the site.
The images below show an extract from the survey drawing showing 3 of the installed stations (shown as triangles) together with an aerial photograph for the same part of the site.