Rain garden

A rain garden is a shallow, planted hollow designed to hold rainwater on site and let it soak into the ground instead of sending it straight to the drains. Water from downpipes, terraces or paved areas is directed into it, ponds briefly, and then moves slowly into the soil through the plants and permeable layers beneath.

How it works and what to watch

As cities gain more impermeable surface, flash flooding and pressure on sewers grow, and a rain garden is a small-scale answer to that. It also traps part of the pollution carried by runoff. Success depends on a few conditions: soil that can take the water, enough distance from the building, a safe overflow route for heavy storms, and plants that cope with both wet and dry spells. Planting is usually layered, with moisture-tolerant species in the centre and drought-tolerant ones around the edges. A properly built rain garden drains within a short time, so it does not breed mosquitoes.

Part of sustainable landscape

Alongside green roofs and permeable paving, rain gardens are a tool of water-sensitive urban design. In visualization, a rain garden with stone edges, gravel and planting shows that a landscape can be both beautiful and useful. For the broader picture, see sustainability and its impact on architecture.