Due to standing water, the runways have at times had to close during the winter months. Specialist consultants were employed to review and recommend improvement works that would resolve this. After a lengthy geological and technical study, they concluded that many areas become waterlogged because water is unable to penetrate the top 18 inches of the surface due to compaction. Below the surface compaction however, there is relatively free draining gravel.
Taking into account these findings, they have recommended that the surface be regraded and a drainage system built into the runways and aircraft movement areas. The drainage design draws the water vertically down in to the free draining sub soil.
The re-grading process involves:
• Remove and discarding of the top 20mm grass and soil
• Remove, grading and retaining 200mm of topsoil
• Using laser guided specialist equipment to regrade the runways and dig drainage channels, which are filled with free draining aggregate. The disturbed area is then resurfaced and re-seeded.
This creates a flat surface, which will also have a gradient (crossfall) of up to 1.5% across the runways to assist with dispersal of surface water.