Infiltration is the process by which (rain)water penetrates the soil through the ground surface and sinks down into deeper soil layers. In construction and garden design, infiltration is used to deliberately return rainwater to the ground locally, instead of discharging it via the sewer.
Why infiltrate?
Because gardens, streets and roofs are increasingly paved over, rainwater finds it ever harder to sink into the soil. During heavy rainfall this leads to flooding and overloading of the sewer, and in dry periods to drought and falling groundwater levels. Infiltration helps to retain the water on site and replenish the groundwater. In many municipalities it is compulsory for new build and renovation to manage rainwater on your own plot.
Infiltration facilities
- Infiltration crates — underground plastic units that temporarily store water and let it seep away slowly
- Gravel pit — a shaft filled with gravel or grit that acts as a buffer space
- Swale (wadi) — a lowered, planted ditch that catches water and lets it infiltrate
- Permeable paving — bricks or slabs through which water can go straight into the soil
Application
- Climate-adaptive building — infiltration absorbs peak downpours and prevents flooding
- Garden design — disconnecting the downpipe to an infiltration facility
- New residential areas — municipal requirements for water storage per square metre of roof and paving
Points to note
- The permeability of the soil (sand infiltrates well, clay poorly) determines whether infiltration works
- Keep the infiltration facility a sufficient distance from the foundation to avoid damp problems
- The groundwater level must be low enough to store water
Related terms
- Rainwater drainage
- Drainage
- Groundwater level
- Climate-adaptive
- Gravel pit
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