These structures can be integrated into urban, peri-urban, as well as more rural landscapes. Rain gardens are particularly used in residential areas, parks and gardens for handling roof runoff and runoff from nearby surfaces, while swales are often used along urban streets, but also alongside agricultural fields. Both structures can be adapted to a variety of landscapes, with careful consideration local spatial features, hydrology and of native vegetation.

Why

Rain gardens and swales can help reduce urban flooding from cloudburst and water pollution (disaster risk and preparedness). These features can also contribute to biodiversity enhancement in cities. By retaining and treating runoff from hard surfaces, they reduce the burden on stormwater systems, improve water quality in recipients by retaining and treating pollutants. Additionally, they provide habitats for native plants and insects. The vegetation in the features enhances infiltration capacity and contribute to purifying the water and air. Moreover, they add aesthetic value to urban and peri-urban areas and contribute to the well-being of communities. 

How

Rain gardens and swales come in many shapes and sizes. They are dimensioned according to the amount of water to handle and the available area for the structure. Site selection and design involves identifying the suitable locations based on runoff patterns, soil type, and space availability.

• Design needs to consider the function of the overall area and landscape they are to be part of, e.g. is it in a public urban park, a school yard, along a busy road or in a private garden.
• The size and depth of rain gardens and the slope of swales are designed to accommodate expected water volumes.
• The soil/filter medium (the infiltration and growth medium) in the rain gardens needs to support both infiltration and plant growth, and sometimes specifically to treat and retain pollutants. It is possible to buy special soils for rain gardens. Existing local soil can sometimes be used in the structures, this could be tested by taking infiltration measures.
• Sometimes additional layer of e.g. biochar is also added to the structures if the primary function is to retain and treat the water from pollutants from e.g. road runoff.
• Sometimes it is relevant to incorporating features like berms or check dams to manage the water flow through the structure.
• In sloped terrain, rain gardens may be built as terraced raingarden to slow down the water and avoid erosion. 

Defined inlets and outlets are important. When establishing the structure, ensure that there is sufficient slope towards the inlet(s) so that the water ends up where it is planned. In some cases, it also be useful to use a “sediment trap” at the inlet of the rain garden to collect gravel and pollutants. 

Plants and vegetation are to be chosen to fit to the local conditions and to tolerate both wet and dry conditions, as raingardens and swales are dry when it do not rain and then need to tolerate a lot of water during heavy rains. Invasive species should not be used. In swales, where water is passing through the structure to a large degree than in a rain garden, erosion-resistant plants are often also chosen.  

Regular maintenance includes weeding, and replacing any plants that do not thrive, checking inlets and outlets and ensuring the system continues to function effectively over time. 

Positive outcomes include reduced runoff and erosion, improved water quality, adding aesthetic and greenery to urban areas. Rain gardens and swales can also serve as educational tools for sustainable water management. While generally beneficial, ensuring that the sufficient and needed maintenance is carried out for the structures to function as intended is important.  

ATTENTION

When implementing rain gardens and swales, several critical considerations ensure their effectiveness:

• A general attention to detail is needed as small design or construction errors can impact the effectiveness of the structures. For instance, improper grading can lead to water pooling in unintended areas, while insufficient soil preparation may result in poor infiltration and plant failure.
• Assessing the catchment area contributing to runoff and design the size and depth of the rain garden or swale accordingly is important to handle the volume of water, especially during peak flow. The excavation depth and contouring must be adequate to ensure that water collects and infiltrates properly. In swales, the slope must be gentle, yet sufficient to facilitate water flow without causing erosion.  
• The soil composition should support both infiltration and plant health. Use quality materials that are suitable for the specific environmental conditions and intended function of the rain garden or swale. Amend soil with organic matter, if necessary (but not too much), to improve infiltration rates but avoid making the soil too loose in swales to prevent erosion. The features sometimes need to be drained, e.g. in clay soil. Clay soil has poor drainage properties, which can cause water to remain in the structure for extended periods leading to plant stress and reduced infiltration efficiency. In such cases, it's common to amend or replace the soil. Additionally, installing an underdrain system can help ensure that excess water is properly managed.  
• It is important to carefully design the inflow points where water enters the rain gardens and swales. It can be relevant to consider the use of downspout redirects, curb cuts, or grading to direct runoff into these features efficiently. It is also important to design an overflow route for extreme rainfall events when the structures are full. This might involve integrating overflow areas within the design or connecting to existing drainage systems while ensuring these do not undermine the structures during normal conditions.  
• Plants play a crucial role in managing water flow and filtration. When selecting and placing plants and other vegetations within the rain garden or swale, it is important to consider root depth, water tolerance, and the plant's role in the ecosystem (e.g., pollutant removal, erosion control), while avoiding the introduction of invasive species. In the context of NBS, it is essential to ensure that these solutions benefit biodiversity. During establishment or in very dry periods, watering the plants may be necessary.
• In places with many people, such as a school yard, it might be necessary to fence the structure while it is under establishment to allow vegetation to grow without being subjected to trampling of people and visits from dogs. Using signs to explain what the feature is can be useful.
• In the winter, plan for snow storage outside and not within the structure itself. Snow may carry gravel and pollutants, which can affect how well the plants emerge in the spring. Runoff from the snow storage can be directed to the rain garden.
• After implementation of the structures, a schedule for regular inspection and maintenance is essential to address any issues promptly. This includes checking for sediment buildup, ensuring plants are healthy, and making any necessary adjustments to inflow points or structures. The level of maintenance needed will depend on the design, size and complexity of the structure.  

There is a substantial body of research and practical guidelines on the design, implementation, and effectiveness of rain gardens and swales, inclusive of studies on their capacity to reduce runoff, improve water quality, and support urban biodiversity. While the principles are well-established, ongoing research aims to optimize designs and maintenance for different environments and climate conditions.  

Specifically, in the Nordic context, the focus includes adaptations to cold climates, managing snowmelt effectively, and incorporating native vegetation that thrives in shorter growing seasons. Such regional adaptation is crucial for ensuring year-round functionality, accommodating our hydrological cycles and addressing urban planning challenges specific to Nordic countries. Nordic-specific research also explores the integration of these features within the existing urban fabric, ensuring they contribute to seasonal aesthetic and ecological goals and to enhancing community well-being.  

Costs

The costs for establishing rain gardens and swales vary based on factors such as size, design complexity, local soils and plant materials, as well as costs of labour. Initial costs typically include design, excavation, soil amendment, and planting. If the features need to be under-drained and the existing soils amended, this will increase the costs. General maintenance costs are generally low, involving periodic weeding and inspection of inlets and outlets to ensure proper function. However, if adjustments need to be made, this will contribute to increased maintenance costs.