In its simplest form, a rain garden is a shallow depression, with absorbent, yet free draining soil and planted with vegetation that can withstand occasional temporary flooding – see the newly dug and planted rain garden in Adastra Park, Hassocks, right.

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Rain gardens are designed to mimic the natural water retention of undeveloped land and to reduce the volume of rainwater running o into drains from impervious areas and treat low-level pollution. In this guide, we also suggest establishing rain gardens in planters, which can receive water from a downpipe.

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Rain gardens were first developed in the United States in the 1990s, where they have become increasingly popular. In the UK, the mimicking of natural drainage in urban areas is socially encouraged and known as Sustainable Drainage Systems (SuDS). This approach is part of a new philosophy to urban water management, developed in Australia, which is known as Water Sensi ve Urban Design (WSUD).

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The term rain garden is wide ranging and has been used to describe a number of different features. However, for the purposes of this guide a rain garden is a simple intervention designed to receive rainwater which has come from a downpipe or a large domestic paved area. The rainwater enters the soil and drains away into the ground or is taken up by the plants and lost back to the air.

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Rain gardens usually absorb all the rainwater that flows into them, but when they do fill up following particularly heavy rainfall, any excess water is redirected to the existing drains. These simple rain gardens do not require any redesign of the existing drainage system and can be installed wherever space permits (see Planning and Design below) and in most soil types.

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WHY RAIN GARDENS

The extensive areas of sealed surfaces, including roofs, pavements and roads, in our towns and cities, cause problems. When it rains, water is normally directed straight to drains, which can be overwhelmed during storms. When this happens, localised flooding can occur, damaging property and blocking streets. In some cities where surface water drains and foul sewers are interconnected, sewage can find its way into watercourses and streets.

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Even when flooding does not occur, runoff may wash oil, heavy metals and other pollutants into watercourses, damaging the plants and animals that live in aquatic environments. Sealed surfaces can also cause problems during warm weather. When the sun shines, more heat is absorbed.

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These problems have become worse as our towns and cities have grown and are expected to be exacerbated by climate change, which is likely to bring about more frequent and heavier downpours and stronger heat waves. One of the most effective ways of tackling these problems and adapting to climate change is to increase the quantity and quality of vegetation and soils. All the green spaces and other environmental features, which include parks, gardens, green roofs and street trees, which are collectively known as green infrastructure, combine to provide various benefits at minimal cost.

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Rain gardens help our gardens to deal more effectively with rainfall, but they also alter and clean runoff . By providing more and more rain gardens, we will be able to reduce our risk of flooding and curb urban heat islands. 

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THE MANY BENEFITS OF GREEN INFRASTRUCTURE INCLUDE:

• Reduced risk of flood

• Reduction in water, air and noise pollution

• Better health through stress reduction and more places to exercise

• Space to relax and play

• Habitat for wildlife and space for people to enjoy nature

• Environmental education

• Local food productionRain gardens can also be planted to attract wildlife and can reduce the cost of maintenance, for example, where frequently mown lawns are replaced.

• They can be easily combined with schemes to harvest rainwater. By increasing the amount of water entering the soil, rain gardens help to reduce the effects of drought and help gardens to thrive without the need for irrigation.Rain gardens work well by bringing about many small incremental improvements, which cumulatively can bring about huge beneficial change – each project, however small, makes a significant contribution towards the over- all goal of making the village greener.​

HOW DO I CREATE A RAIN GARDEN

To find out what to do from planning to building and what plants to use see this guide with images and detailed suggestions.

http://raingardens.info/wp-content/uploads/2012/07/UK-Rain-Garden-Guide.pdf