A rain garden is a planted depression that receives run-off, holds water temporarily and encourages infiltration or controlled release.
A rain garden is a planted depression that receives run-off, holds water temporarily and encourages infiltration or controlled release. It is not just a lower bed. It needs a known contributing area, suitable soil, a protected inlet, storage volume, a safe overflow, compatible plants and maintenance.
Define where the water comes from and where it goes
The system may receive water from roofs, footpaths or car parks. The contributing area and the rainfall intensity determine the volume that arrives. Without this reading, a depression may be undersized or receive more sediment than it can handle.
The overflow must carry away events greater than the garden’s capacity without flooding buildings or eroding the ground.
Soil and construction are part of the system
Infiltration depends on permeability and on the water table. In very slow soils, a drain, a filter layer or controlled discharge may be needed. In contaminated soils, infiltration may be inappropriate.
The inlet should dissipate energy and trap sediment. The finished level and the thickness of the layers need to be checked on site.
Plants for alternating dry and wet
The centre receives more water and may stay saturated for longer; the edges dry out more quickly. The palette should be distributed along this gradient, not treated as a single zone.
Maintenance includes removing sediment, clearing inlets, replacing plants and checking the overflow. A rain garden is only a nature-based solution while it goes on solving the hydraulic problem.
What undermines the result
The most common mistakes are sizing by visual area alone; not providing an overflow; using wet-soil plants across the whole section; and leaving the inlet and the drain without access.
Applying it to the project
At Diaplant, the rain garden is treated as a built system: it receives a defined area, stores water temporarily, has an overflow and uses plants compatible with alternating dry and wet conditions.
The planting brings the system to life, but effectiveness begins with the hydraulics. A well-designed rain garden combines water, soil, levels, vegetation and maintenance.
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