A rain garden is a planted area designed to reduce the amount of water running off into drainage systems. It works by slowing down the flow of water giving the soil and plants time to absorb as much as possible, by slowing the water down it minimises the impact of high rain fall giving the wider water distribution system time to cope and reducing the risk of flash flooding.
The construction of a rain garden varies hugely in its complexity, with the absolute basic being the redirecting of a water down pipe into an adjacent border, to a sophisticated SuDS scheme with carefully calibrated water flow rates and control valves.
Within the domestic landscape, rain gardens can be used to manage the surface water which is created by rain falling onto roofs, patios and paths thus reducing the need to install often costly, underground drainage systems. This has the effect of also reducing the amount of water entering the sewerage network which often becomes overwhelmed during storm events and directly contributes towards the pollution of rivers and streams.
If the garden is expected to receive a high volume of water and is not expected to be able to soak away the full volume then a drainage system will still be required to remove the excess water.