A gravel drainage trench, also known as a soakaway, is a trench or pit filled with gravel or chippings that temporarily collects rainwater and lets it soak slowly into the surrounding ground. It is a simple form of infiltration in which rainwater is dealt with locally instead of being piped away to the sewer.
How does it work?
Gravel is highly permeable and, at the same time, holds open space between the grains. Rainwater from a roof or paving is led into the trench through a pipe or by a slight fall. The voids between the gravel grains buffer the water, which then gradually infiltrates into the surrounding soil.
The storage capacity depends on the volume of the trench and the void ratio of the gravel (usually 30 to 40 per cent). The infiltration rate is governed by the permeability of the soil.
Application
A gravel drainage trench is used for:
- Rainwater management — disconnecting rainwater from the sewer
- Gardens and drives — collecting run-off from paving
- Climate-adaptive building — reducing flooding during heavy downpours
- Drainage — keeping foundations and basements dry
In poorly draining soil such as clay, a gravel trench works less well and an infiltration crate or another solution is needed.
Related Terms
- Infiltration
- Drainage
- Rainwater drainage
- Gravel
- Gravel concrete
More guides and plans available at fredsdiyplans.com