Rain Gardens – small gardens, a big deal
The development of cities and replacement of permeable areas – e.g. green areas – with impermeable ones adds to the disturbance of the natural water circulation. It reduces water infiltration and evapotranspiration while the surface runoff increases significantly. Also the climate changes that we experience with greater and greater intensity have contributed in recent years to more frequent flooding and floods in urbanised areas – the so-called flash floods – sudden local floods occurring most often after dry weather periods (urban droughts).
These are not the only consequences of these two factors – there are also lower supply of groundwater and change of the city microclimate. In addition, the surface runoff washes off pollution from the catchment area – from streets, roofs, industrial areas or petrol stations – and transports it to the storm water drainage and/or directly to the surface waters.
In light of the above, steps taken in order to implement sustainable storm water management consist of building the devices and facilities aimed at retention, infiltration and treatment of storm waters on various levels, including districts, streets or residential buildings.
Efficient storm water urban surface retention system (SWUSRS) must provide retention in many dimensions, in which all retention levels are equally important and complementary to one another.
Such multi-level retention should provide as many ecosystem services as possible and create sustainable environment for human activities.
A very important aspect here is the need for resident participation in the planning process, essential for social acceptance but also encouraging the residents to feel co-responsible for the city.
Therefore, rain gardens are a great example of micro scale retention. They ensure retention and infiltration of storm water with its simultaneous treatment through filtration. Plants contribute to the enhanced pollution removal efficiency. The rain gardens are easy to create and blend with the surroundings. They also require little space and when designed and tended to appropriately they offer undeniable aesthetic value. This is a solution promoted especially in the districts with single family housing.
There are numerous construction solutions which might be applied when creating a rain garden, from the easiest dry ditch with stones and plants to the replacement of soil with gravel in order to increase retention and infiltration capacity. It is assumed that a rain garden absorbs 30-40% more water than a lawn of a similar size. It is also worth noting that such plant gathering with water reserve maybe an attractive habitat for birds, insects, frogs, toads and grass snakes. Let us remember – the greater biodiversity the better chance at sustainable environment that we live in.