Drainage removes excess water from lawns, sports facilities, planting holes and pavements. Here is the drainage technique: drain pipes and materials, fall and depth, sediment traps and cleaning wells, perimeter drainage and connection — and the pitfalls that most often cause drainage failure.
Introduction
Drainage leads excess water away from the soil so roots don't drown, lawns don't become waterlogged and pavements don't lose bearing capacity. Drainage is basic landscape engineering — and at the same time a common failure source, because a drain laid without fall, without trap or in unsuitable soil fails quietly, long after the work is handed over.
When should it be drained?
- 01Wet, heavy soil or high groundwater, where water stands after rain.
- 02Lawns and sports facilities that must be usable shortly after rain.
- 03Planting holes in heavy clay soil where water otherwise stands in the hole and chokes the roots.
- 04Terrain and buildings where a perimeter drain keeps water away from foundation and cellar.
- 05Under and around fasteners where foundation stabilization and drainage together keep the structure dry and bearing.
Drain pipes and materials
- 01Drainage pipe: perforated pipe (typically PVC or PP) that collects water from the soil. Laid with perforation facing down so water can enter.
- 02Wrapping / filter: pipe wrapped with coconut coir or geotextile is used in fine-grained soil so the drain does not clog with soil particles.
- 03Drainage gravel/drain box: a layer of coarse, draining gravel (or a drain box) around the pipe that directs water to it and keeps fines out.
- 04Geotextile: separates drainage gravel from the surrounding fine-grained soil, so the gravel is not clogged (DS/EN 13252 for drainage geotextiles).
Fall, depth and distance
A drain must have a fall so the water runs toward the outlet. According to common Danish practice drain pipes are laid with approximately 3 ‰ fall, in a straight line without pockets where water otherwise collects. Drain depth and the distance between drain lines depend on the soil type: the more clayey and tight the soil, the closer the drains must be to dry it out, while sandy soil manages with greater distance. Determine depth and distance according to soil and purpose (Pipe Centre's/SEGES' guidance on field drains), not according to a fixed figure.
Sand trap and sump wells
- 01Sand trap: a pit with a sediment chamber that traps sand and fine material before the water runs on — placed before outlet, soak-away or sewer connection and must be able to be emptied.
- 02Flushing/inspection wells: provide access to flush and inspect the drain; placed at direction changes and at appropriate intervals on long stretches.
- 03Cleanability: a drain that cannot be flushed and inspected cannot be maintained — plan access from the start.
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