Incorporating stakeholders’ preferences into a multi-criteria framework for planning large-scale Nature-Based Solutions

Hydro-meteorological risks are a growing issue for societies, economies and environments around the world. An effective, sustainable response to such risks and their future uncertainty requires a paradigm shift in our research and practical efforts. In this respect, Nature-Based Solutions (NBSs) offer the potential to achieve a more effective and flexible response to hydro-meteorological risks while also enhancing human well-being and biodiversity. The present paper describes a new methodology that incorporates stakeholders’ preferences into a multi-criteria analysis framework, as part of a tool for selecting risk mitigation measures. The methodology has been applied to Tamnava river basin in Serbia and Nangang river basin in Taiwan within the EC-funded RECONECT project. The results highlight the importance of involving stakeholders in the early stages of projects in order to achieve successful implementation of NBSs. The methodology can assist decision-makers in formulating desirable benefits and co-benefits and can enable a systematic and transparent NBSs planning process. Electronic supplementary material The online version of this article (10.1007/s13280-020-01419-4) contains supplementary material, which is available to authorized users.


Hydro-meteorological Risk
This goal represents the hydro-meteorological risk that is present in the chosen area and reflects the need for reducing it.
Water Quality This goal indicates the importance of improving the overall water quality, including surface and groundwater bodies in the investigated area. Water quality is an essential factor since it interrelates with other factors such as ecosystems and human health.
Habitat structure The habitat structure category determines the main aspects related to habitat quantity and quality in the area. This includes the importance of increasing habitat area, habitat provision and distribution, ecological status and physical structure of habitats and land use type.

Biodiversity
The biodiversity refers to the variety of life on earth at all its levels, from genes to the ecosystem. It presents the status of ecosystems and enhances local biodiversity in order to create conditions where various species can thrive in abundance and live without disturbance.

Social-Economic
This goal relates to the people living in the chosen area or those affected by current developments. This category reflects on the need or the present opportunities that are needed to increase socio-economic development in the area. It includes factors such as recreational space, educational opportunities, and community cohesion.
Human well-being This goal relates to the enhancement of human well-being benefit in the area from implementing NBS. The importance of this category reflects on health and well-being such as mental well-being, physical activities/health, urban heat island effect mitigation, air pollution improvement through capture/removal by vegetation etc.

Improve water quality in rivers/watercourses, lakes/ponds
This sub-goal indicates whether the improvement of water quality in surface water bodies like rivers and lakes is required. Change in water pollution (i.e., both point sauces and non-point sources), heavy metals, nutrient contamination and sediment deposition, are important key indicators, which can lead towards problems for ecological and human health.

Improve coastal water quality
This sub-goal reflects on the water quality in coastal areas. The main key factor here is the pollution level of coastal waters. Most ocean pollution is influenced by the land, either along the coastline or coming from the. It causes dangerous conditions for marine life and human health.

Improve groundwater quality
Groundwater is a very important source in terms of drinking water supply in many nations. Groundwater quality is less prone to contamination than surface water but can also be affected by various pollution sources and infiltration through the soil. The indicators can be attenuation of pollution in groundwater, change in soil quality or seawater intrusion.

Increase habitat area (quantity)
This sub-goal focuses on the importance of increasing the habitat area (i.e., change in riparian, aquatic, wetland and terrestrial habitats for local species). The size of the habitat has significant effects on reproduction and population persistence for various species. Increasing green space can improve population growth and reduce the risk of species extinction.
Habitat provision and distribution (quality) Habitat provision and distribution refers to the quality state of a habitat. This can be seen in the distribution of green space in the area and whether habitat structures are showing good connectivity with each other. Better connectivity of habitat structures leads to a higher ecosystem function where higher diversity of animal and plant species can be found, leading to better overall ecosystem health.
To reflect the ecological status and physical structure of habitats This sub-goal indicates the significance of carrying out conservation and protection strategies to reflect on the ecological status and physical habitat structure of the area. This can be done by monitoring changes of vegetation, erosion protection and the overall conservation status and by looking at possible trends and future projections.
Land use type This sub-goal relates to the type of land that could potentially be used or changed to implement a possible NBS. A low impact space (e.g. rooftop) can be used to increase its values of ecosystem services and functions. Often compromises are needed to prevent conflicts in those areas and provide sustainable solutions.
To maintain and enhance biodiversity This sub-goal relates to the importance of maintaining and enhancing biodiversity, which means improving number and types of protected species, native species and their density and diversity in general.

Reduce disturbance to ecosystems
Reducing the disturbance to the ecosystem, in this case, means to decrease stressing ecological factors in the area such as specific amounts of nonnative/migrated and invasive species that could be a threat to the local ecosystem or local species.

Increase recreational opportunities
Increased recreation opportunities mean providing recreational space, giving the possibility to people to spend their free time in the area, engaging livelihood activities and increasing number of tourists. These can be beneficial for human well-being from both biological and psychological aspects.

Education and awareness
A site can be seen as an opportunity to provide knowledge and awareness about connected key aspects such as the reduction of major risks (e.g. flooding) in the area as well as supporting ecosystems.

Maintain and if possible enhance cultural values
Maintaining and (if possible) enhancing cultural values present in the area includes reducing the risk of losing cultural heritage during extreme weather events. Also, it means to improve working environments for local food production and to maintain or increase numbers of cultural events.

Accessibility
Accessibility reflects on the factor of how easy it is to reach/ access the NBS site. It includes free space of the area and connection between area and surrounded homes.

Improve Community Cohesion
Improve community cohesion is enhanced when the people are engaged in an activity which connects them. This also includes the number of people who communicate with the neighbourhood in the NBS area and cognitive and social development in children and young people.

Stimulate/increase economic benefits
This sub-goal shows the significance of increasing or stimulating economic growth in the area. This includes factors such as avoided future damage costs and reduced costs from energy and carbon saving through NBS (e.g. reduced energy consumption of buildings). Also, factors can be seen in reducing the costs of negative health impacts and an increase in property values.
Encourage new business models and other community benefits provided by NBS This sub-goal refers to the opportunity of encouraging new business models and community benefits to arrive through a NBS. Due to increasing attractiveness of the area, new businesses could be interested in settling, also through the improvement of living and working conditions. Furthermore, this could mean an increase in created green jobs in the area.

Direct health and wellbeing impacts
Direct health benefits can be considered in terms of mental and physical well-being. One of the main reasons why an NBS could improve human health can be seen in the fact that it allows increasing physical activity to the people who live or visit the area, spending more time outside and being more engaged within the community.

Indirect health and wellbeing impacts
Indirect health impact can be seen due to improving air quality (e.g. removing pollution with planted vegetation), less noise pollution, possible reduction of heavy metal contents in the environment and the mitigation to the urban heat island effect. NBS can reduce the exposure level of toxic substances towards humans and can be beneficial in terms of human health.

Maintain and if possible enhance cultural values
Loss of cultural heritage due to hydro-metrological events/ due to land take Food production Number of cultural events in NBS area

Sub-Goals
Indicators that used to assess the performance of sub-goals Accessibility Accessible NBS area per capita Footpath network recover through erosion reduction and improvement of path smoothness Average journey time for people by foot to NBS area or average distance from home/public transportation to NBS area

Improve Community Cohesion
The number of people communicate with neighbourhood in the NBS area Cognitive and social development in children and young people Community development and cohesion Encourage new business models and other community benefits provided by NBS Number of subsidies or tax reductions applied for (private) NBS Number of new businesses attracted from NBS Number of green jobs created Enhancing attractiveness of places for living and working, and to visit Gross value added per employees based on full-time equivalent jobs in the green sector. Finances and willingness to pay Increased competitive advantage for cities applying NBS

Stimulate/increase economic benefits
Reduced/avoided damage cost from hydro-meteorological risk reduction Economic benefit from the reduction of stormwater that typicaly needs to be treated in a public sewerage system Energy and carbon savings from reduced building energy consumption (heating and cooling) Reduce cost of health impacts of air and noise pollution Value of reduced CO2 emission and carbon sequestration Reduced need for management and maintenance Change in land and/or property values

Direct health and wellbeing impacts
Mental well-being Physical health/activities General self-rated health Reduction in chronic stress and stress-related diseases Reduction in number of cardiovascular morbidity and mortality events Episodes of water-borne diseases Indirect health and wellbeing impacts Urban heat island effect mitigation Increase in pathogen vector habitat Change in heavy metal emission Avoided greenhouse gas emissions [should this be in Nature section? very long term indirect relationship to human health and wellbeing] Air pollution improvement through capture/removal by vegetation Noise pollution attenuation

Introduction to the project
The RECONECT project aims to develop a framework that can help affected people and involved stakeholders to find suitable and sustainable solutions for their area. The project focusses in selectin and evaluating measures that are known as 'Nature-based solutions' (NBS). NBS have been proven in many cases that they are beneficial in terms of flood risk reduction and other types of hazards. In comparison to the traditional grey infrastructure, NBS can give the opportunity not only to fulfil one single purpose (e.g. reducing the flood risk) but also to provide valuable co-benefits to the ecosystem and human well-being as well as climate resilience. More information about the project can be found on the website (www.reconect.eu).

Survey description
Since not all measures are suitable for all locations and all hazard types, six filters are used in this process to narrow down the list of measures. Therefore, this survey is conducted in order to collect valuable data for these six filters, which will contribute to Preliminary selection measure process (See Figure below). The outcome will be seen as suitable measures for a specific situation.
6 filters that are used to narrow down the list of measures that have potential to reduce the local hazards in the particular affected area are described below. The criteria area; measure type, hazard type, affected area, potential location for implementation of measures, type of project, and land surface type.

Affected area
Please select the area that have been affected by the hazard (you can select more than one) ☐ Urban area ☐ Non-urban area

Potential location for implementing measures
If your area is urban area please select ☐ If your area is non-urban area please select below (you can select more than one);

Middle course (Middle of river) ☐
Lower course (floodplain and Delta area) ☐

type of project
Please select type of project that you wish to implement in order to reduce local risk (you can select more than one) ☐ Implementation of new measures ☐ Improvement or expansion of existing measures

Land surface type
Please select Land surface type that you wish to implement in order to reduce local risk (you can select more than one) The RECONECT project aims to develop a framework that can help affected people and involved stakeholders to find suitable and sustainable solutions for their area. The project focusses in selectin and evaluating measures that are known as 'Naturebased solutions' (NBS). NBS have been proven in many cases that they are beneficial in terms of flood risk reduction and other types of hazards. In comparison to the traditional grey infrastructure, NBS can give the opportunity not only to fulfil one single purpose (e.g. reducing the flood risk) but also to provide valuable co-benefits to the ecosystem and human well-being as well as climate resilience. More information about the project can be found on the website (www.reconect.eu).

Survey description
This survey is conducted in order to collect valuable data, which will contribute to the of the feasibility selection process of NBS measure. Collected inputs will be used for a Multi-criteria Analysis (MCA). The outcome will be seen as feasible measures to discuss possible solution opportunities for the existing problems in the area. This process is done with multiple stakeholders in order to reflect on all involved stakeholder opinions and to form a conclusion based on expert knowledge, local opinions, and knowledge from involved people in the area.

Filling in Weights for Goals/Sub-goals
In the next section (Weighting of Goals & Sub-goals), you will find the Goals & Sub-goals that are included in the NBS selection and evaluation process. You are asked to give weight on those Goals & Sub-goals based on your knowledge of the area and your opinion of the importance to address the specific Goal or Sub-goal. Description of Goals & Sub-goals can also be found in the next section.

Increase habitat area (quantity)
This sub-goal focuses on the importance of increasing the habitat area (i.e., change in riparian, aquatic, wetland and terrestrial habitats for local species). The size of the habitat has significant effects on reproduction and population persistence for various species. Increasing green space can improve population growth and reduce the risk of species extinction.
What importance do you place on increasing room for habitat in the area? Put Weight here (0-10): Give an explanation of the given weight:

Habitat provision and distribution (quality)
Habitat provision and distribution refers to the quality state of a habitat. This can be seen in the distribution of green space in the area and whether habitat structures are showing good connectivity with each other. Better connectivity of habitat structures leads to a higher ecosystem function where higher diversity of animal and plant species can be found, leading to better overall ecosystem health.
What importance do you place on improving the quality of habitat in the area, such as habitat connectivity? Put Weight here (0-10): Give an explanation of the given weight:

To reflect the ecological status and physical structure of habitats
This sub-goal indicates the significance of carrying out conservation and protection strategies to reflect on the ecological status and physical habitat structure of the area. This can be done by monitoring changes of vegetation, erosion protection and the overall conservation status and by looking at possible trends and future projections.
What importance do you place on reflecting the ecological status and physical habitat structure in the area? Put Weight here (0-10): Give an explanation of the given weight:

Land use type
This sub-goal relates to the type of land that could potentially be used or changed to implement a possible NBS. A low impact space (e.g. rooftop) can be used to increase its values of ecosystem services and functions. Often compromises are needed to prevent conflicts in those areas and provide sustainable solutions.
What importance do you place on choosing the right land-use type for possible implementation in the area? Put Weight here (0-10): Give an explanation of the given weight:

To maintain and enhance biodiversity
This sub-goal relates to the importance of maintaining and enhancing biodiversity, which means improving number and types of protected species, native species and their density and diversity in general.
What importance do you place on the maintenance and enhancement of biodiversity in the area? Put Weight here (0-10): Give an explanation of the given weight:

Reduce disturbance to ecosystems
Reducing the disturbance to the ecosystem, in this case, means to decrease stressing ecological factors in the area such as specific amounts of non-native/migrated and invasive species that could be a threat to the local ecosystem or local species.
What importance do you place on reducing the disturbance to ecosystems in the area? Put Weight here (0-10): Give an explanation of the given weight:

Increase recreational opportunities
Increased recreation opportunities mean providing recreational space, giving the possibility to people to spend their free time in the area, engaging livelihood activities and increasing number of tourists. These can be beneficial for human well-being from both biological and psychological aspects.
What importance do you place on increasing recreational opportunities in the area? Put Weight here (0-10): Give an explanation of the given weight:

Education and awareness
A site can be seen as an opportunity to provide knowledge and awareness about connected key aspects such as the reduction of major risks (e.g. flooding) in the area as well as supporting ecosystems.
What importance do you place on increasing or improving educational/awareness opportunities through NBS in the area? Put Weight here (0-10): Give an explanation of the given weight:

Maintain and if possible enhance cultural values
Maintaining and (if possible) enhancing cultural values present in the area includes reducing the risk of losing cultural heritage during extreme weather events. Also, it means to improve working environments for local food production and to maintain or increase numbers of cultural events.
What importance do you place on maintaining or enhancing cultural values in the area? Put Weight here (0-10): Give an explanation of the given weight:

Accessibility
Accessibility reflects on the factor of how easy it is to reach/ access the NBS site. It includes free space of the area and connection between area and surrounded homes.
What importance do you place on the accessibility to an NBS in the area? Put Weight here (0-10): Give an explanation of the given weight:

Improve Community Cohesion
Improve community cohesion is enhanced when the people are engaged in an activity which connects them. This also includes the number of people who communicate with the neighbourhood in the NBS area and cognitive and social development in children and young people.
What importance do you place on improving community cohesion in the area? Put Weight here (0-10): Give an explanation of the given weight:

Stimulate/increase economic benefits
This sub-goal shows the significance of increasing or stimulating economic growth in the area. This includes factors such as avoided future damage costs and reduced costs from energy and carbon saving through NBS (e.g. reduced energy consumption of buildings). Also, factors can be seen in reducing the costs of negative health impacts and an increase in property values.
What importance do you place on stimulating/increasing economic benefits in the area? Put Weight here (0-10): Give an explanation of the given weight:

Encourage new business models and other community benefits provided by NBS
This sub-goal refers to the opportunity of encouraging new business models and community benefits to arrive through a NBS. Due to increasing attractiveness of the area, new businesses could be interested in settling, also through the improvement of living and working conditions. Furthermore, this could mean an increase in created green jobs in the area.
What importance do you place on encouraging new business opportunities and benefits to the community in the area? Put Weight here (0-10): Give an explanation of the given weight:

Direct health and well-being impacts
Direct health benefits can be considered in terms of mental and physical well-being. One of the main reasons why an NBS could improve human health can be seen in the fact that it allows increasing physical activity to the people who live or visit the area, spending more time outside and being more engaged within the community.
What importance do you place on improving direct health impacts in the area? Put Weight here (0-10): Give an explanation of the given weight:

Indirect health and well-being impacts
Indirect health impact can be seen due to improving air quality (e.g. removing pollution with planted vegetation), less noise pollution, possible reduction of heavy metal contents in the environment and the mitigation to the urban heat island effect. NBS can reduce the exposure level of toxic substances towards humans and can be beneficial in terms of human health.
What importance do you place on indirect health impacts in the area? Put Weight here (0-10): Give an explanation of the given weight:

An explanation
This section provides some information about NBS measures. Definition, primary function and co-benefits are given for each NBS measure, with a picture that should give a better understanding of how the measure would look like in reality.
Weights should be given with values from 0 to 10 in order to show the suitability to address the present issues and developments in the area. A value of 0 represents inapplicable/unsuitability, whereas 10 means that the measure is very suitable.

Floodplain excavation/enlargement/restoration
A floodplain is an area bordering a river that naturally provides space for the retention of floods and rainwater. Floodplains have often been drained, and in many places, they have been separated from the river by structures.
The floodplain can be enlarged by lowering the level or/and increasing the width of the floodplain area. An area of the floodplain increases will create more room for the river during high flow by increasing the discharge capacity and provide upstream retention.
Sediments can also cover the floodplains. By allowing the natural functioning of rivers, floodplain restoration measures have high potential to control runoff and reduce flood risk, since they should aim to maximise the capacity of the floodplain to store river water. The associated changes in land use and reduction in surface-runoff can lead to higher recharge of water into the ground. Increased organic matter content can increase soil water retention, while removal of sediment improves soil permeability.

Co-Benefit:
The floodplain excavation creates opportunities for nature and recreational development. With a significant change of land cover, it can reduce pollution by activating filtration by vegetation and soil. Floodplain restoration enables recovery of natural erosion and sedimentation processes, therefore reducing sediment transport downstream. Floodplain contributes to creating terrestrial, aquatic and riparian habitats, increasing fish populations, improving biodiversity and providing natural biomass. The restoration site can be planted with native grasses, shrubs, and trees, which will discourage the establishment of invasive vegetation.
Floodplains are likely to contribute to climate change adaptation through the fixation of carbon dioxide by photosynthesis and C-burial. They also provide recreational opportunities and aesthetic value.
Put Weight here (0-10): Give an explanation of the given weight:

Depoldering
The dike on the riverside of a polder is relocated land-inwards, which return the polder to the river. This way, the river has more room for flooding due to the water can flow into the area at high water levels.
A new dike is built further inland. Breaches are created in the old dikes, allowing the tides to flow in and out of the area. This is how tidal nature, with mudflats and marshes, develops in the depoldered area. At the same time, the force that the water exerts on the dikes is tempered, reducing the likelihood of floods further inland.

Co-Benefit:
Depoldering creates opportunities for nature habitat developments as well as improve aesthetic value in the area. It also offers opportunities for recreation activities and economic activity.
Put Weight here (0-10): Give an explanation of the given weight:

Widening of water bodies
The river width is an activity which aims to increase the conveyances characteristics of the river though widening by excavating the embankment. The widening rivers provide more space in the river. By enlarging the cross-sectional area, it increases the bank discharge of the river along with its hydraulic radius. This will increase the velocity of the river and reduce the chances of it flooding in the immediate area by moving the floodwater further on downstream.
Co-Benefit: Channel migration and braiding are enabled within the widened reach, leading to greater structural, hydraulic, and habitat heterogeneity. The exchange between the water column and channel bed and river banks (vertical and lateral linkages) can affect water quality because these are biogeochemically active areas where organic matter decomposition and nitrogen removal occurs.
Put Weight here (0-10): Give an explanation of the given weight:

Deepening water bodies
The water body bed is deepened by excavating the surface layer of bed to increase the depth of water bodies such as rivers, canals or ponds. The deepened water body bed provides more room for the water.
Increasing the depth of water bodies is also increasing the storage volume. The amount of water which can be stored in this way can become available when water is scarce. The water bodies are refilled when water is abundant during wet periods. Deepened water bodies help to reduce flood risk as rivers can transport a larger amount of water to downstream and ponds and lakes have a larger retention capacity.

Co-Benefit:
Deepening water bodies contributes to improving the status of Physico-chemical and hydro-morphology quality elements. Diversifying water depth contributes to improving the diversity of habitats offered by the river and to create new habitats. Deepening water body also fosters the development of riparian habitats on river banks. This leads to enhanced natural biomass production and helps to create and preserve biodiversity. The measure also contributes to better management of fish stocks and helps to improve the status of biology quality elements and prevent surface water deterioration. Deepening water bodies can provide recreational opportunities (through the diversification of the activities offered by the river) and aesthetic value.
Put Weight here (0-10): Give an explanation of the given weight:

Lowering groynes
Groynes stabilise the location of the river and ensure that the river remains at the correct depth. However, at high water levels groynes can form an obstruction to the flow of water in the river. Lowering groynes increases the flow rate of the water in the river.
. A perpendicular groyne is constructed at a right angle to the flow of the river. These groynes will be lowered or removed. By lowering the groynes in the river and building parallel barriers, the river will be able to drain excess water easier Co-Benefit: Lowering the groynes are more navigable depth for shipping and wet banks at low water levels during dry periods. In the side stream of lowering groynes, development of flora and fauna is expected to improve along the river banks.
Put Weight here (0-10): Give an explanation of the given weight:

Bypass/diversion channels
Bypass channels divert river flows at a point upstream of an area. These diverted flows can be discharged back to the same river (Bypass channel), or into another natural drainage system nearby (Diversion channel). Gates usually use to regulate flows into bypass and diversion channels. The measure implies 'giving back' floodplain area to the river. It is a separate channel into which floodwaters are directed to lessen the impact of flooding on the main river system.

Co-Benefit:
Apart from enhancing the rivers' capacity, many secondary benefits are produced such as increasing groundwater infiltration, improving water quality, restoring natural floodplain forming processes (e.g., sediment transport and deposition) and improving fish and wildlife habitats. (FEMA, Floodplain Natural Resources and Functions, accessed on Sept. 2018) With reduced flows in the main stem of the river, streamside vegetation can encroach into the river channel, thereby changing its physical and biological characteristics and restoring the natural floodplain ecosystem. The in-stream habitat component is providing good elements of abundant cover, clean substrates and high base flows, which assures a stable water supply with adequate depths and flow during droughts.
Recreational opportunities can best be enhanced by developing additional access facilities on the diversion channel to relieve current crowded conditions. Put Weight here (0-10): Give an explanation of the given weight:

Reconnection of oxbow lakes and Re-meandering
Oxbow lakes are former meanders that have been cut off from the river, thus creating a small lake with a U form. Oxbow lakes occur naturally, but may also occur due to artificial river straightening. Reconnecting an oxbow lake/re-meandering involves removing terrestrial lands between both water bodies, therefore favouring the overall functioning of the river by restoring lateral connectivity, diversifying flows and cleaning the river section of the present oxbow, and thereby providing better water retention during floods.

Co-Benefit:
Oxbow lakes and reconnected side arms may play an important role in creating habitats, but care should be paid not to destroy pre-existing oxbow lake habitats. Often these habitats are used for spawning places by fish and other aquatic groups so that fish stocks can increase. That, in turn, contributes to improving the status of biology quality elements.
Bank vegetation often expands after reconnection because of improved water regime, and populations of water birds, amphibians, reptilian and mammal species can increase.
Restoration of natural green areas significantly contributes to the 2020 Biodiversity Strategy and provides aesthetic and cultural value.
Put Weight here (0-10): Give explanation of the given weight:

Retention ponds
Retention ponds are ponds designed with additional storage capacity to attenuate surface runoff during rainfall events. Ponds are created by using an existing natural depression, by excavating a new depression, or by constructing embankments. Increasing storage can be applied on different scales.
Retention ponds reduce peak runoff through storage and controlled outflow and reduce the risk of surface flooding in conjunction. Reduction of discharge causes lower water levels downstream of the site of the measures.

Co-Benefit:
Retention basin also help to prevent downstream erosion, and improve water quality in an adjacent river, stream, lake or bay thought vegetation. Sometimes they act as a replacement for the natural absorption of a forest, or other natural proves that was lost when an area is developed.
Retention ponds can be effective at pollutant removal. They are also highly effective at intercepting sediment. Through reducing diffuse pollution, retention ponds play a role in preserving and improving surface water quality.
Creation of ponds will create new aquatic and riparian habitat, therefore increasing natural biomass production and contributing to biodiversity preservation.
Retention ponds can contribute to more sustainable agricultural practices. Ponds also increase the aesthetic/cultural value of the landscape.
Put Weight here (0-10): Give an explanation of the given weight:

Detention basins
A detention basin is a free space from water in dry weather. It designs to store runoff for temporary during high flow then releasing it slowly to downstream or a nearby watercourse, using an outlet control structure to control the flow rate.
Detention basins are vegetated depressions designed to hold runoff from impermeable surfaces and allow the settling of sediments and associated pollutants. They are not designed to allow infiltration. The storage capacity is dependent on the design of the basin, which can be sized to accommodate any size of the rainfall event. Detention basins can reduce the risk of surface flooding in conjunction with other NBS features, and in doing so, contribute to climate change adaptation.
Co-Benefit: Detention ponds and basins can be effective at capturing sediment in urban or rural runoff and at pollutant removal, as a result of the settling of particulate pollutants and uptake by vegetation. Therefore, they have the potential to improve water quality in receiving water bodies by addressing diffuse urban pollution and reducing chemical pollution.
Detention basins may provide minor biodiversity benefits (although unlikely to provide significant habitat improvements). Where used to intercept and store runoff from low permeability surfaces in agricultural areas, detention basins can contribute to more sustainable agricultural practices. By creating green areas, they provide aesthetic and recreational benefits.