Water sensitive urban and building design

The local context and what kind of WSUD has been planned or implemented defines who are the key stakeholders to engage. If design is more focused on a block or at building level, key stakeholders for participation are property owners, investors and property managers. If the main issue is about stormwater management solutions as a part of urban planning, collaboration between different sectors (land use, environment, and transportation), experts (e.g. researchers) and land owners is needed. Depending on the case and spatial scalability of the system (e.g. biofilter at the street level vs. large-scale stormwater pond) there might be also other stakeholders that have an interest or can influence the implementation of the plan. Broader flood risk management requires long-term collaboration among local and regional authorities, and with those stakeholders who have responsibilities in implementing the plan, such as land or property owners. In order to enhance public acceptance of different WSUD solutions, it is necessary that the general public, citizens and local residents are engaged at the early stage of the planning and design. Novel funding models such as public-private partnerships require close collaboration with the private sector, especially if they are part of implementation process. 

The importance of institutional frameworks (governance and management) for successful and widespread implementation of these measures is considered central. Planning processes require earlier and more intense consultation with different planning authorities.  

An important success factor for the implementation of WSUD by private households is the funding scheme. Governments can also subsidize investments to improve water management and use in cities. For example, the domestic use of rainwater for non-potable uses in Bremen (Germany) was encouraged by an investment subsidy provided by the Federal State. 

Main enablers include partnership among stakeholders, effective monitoring and valuation systems for implementation process and benefits, knowledge sharing mechanisms and technologies, economic instruments, plans, acts and legislations, education and training, open innovation and experimentation, and appropriate planning and design of sustainable solutions.  

Conversely, there are many uncertainties related to the implementation of WSUD that can limit its implementation. They mainly relate to inadequate financial resources, limited space and time availability, institutional fragmentation, lack of knowledge and inadequate regulations. 

Investments for WSUD may increase total costs of construction, planning and management work, but on the other hand can reduce negative impacts for citizens, buildings and the entire city, and decrease unexpected costs to repair damages caused by extreme weather conditions such as flooding or stormwater run-off. Implementing WSUD for stormwater management instead of traditional sewage systems can lower rainwater fees (that are generally based on the extension of impervious property surface, which directs rainwater into the public sewage system) of private households or block of houses (Rainwater saving and use in households, Bremen).  

Rainwater storage facilities at building level can cost at least 6000 € (Rainwater saving and use in households, Bremen) but can be higher for larger interventions (€17.500 for rainwater storage facility of a climate proof building block, Amsterdam). 

Cost-effectiveness of investments should be estimated in the local context since they depend on local climate and environmental conditions (e.g. precipitation, proportion of paved soil, density of built environment) and economic factors (e.g. prices of water). Total costs also depend on the size, technical complexity and required intensity of maintenance. Recent studies of costs of different nature-based solutions (e.g. green roofs, biofilters, rain gardens etch) have brought some insights on potential costs of WSUD. For example, in Finland the implementation costs of stormwater pond (size 10 000 m2) varied between 240 000- 600 000 euros (CITYWATER project). Construction costs of green roofs can significantly vary (60-500€/m2, Nurmi et al., 2013) between countries and based on the roof type, vegetation planted, technical requirements etc.  

WSUD reduces stormwater flood risks (area and people flooded) in urban areas. Other benefits include the reduced stress on water resources by decreasing the likelihood of overexploitation of water and increasing water availability. Nature-based solutions in WSUD usually provide multiple benefits by enhancing recreational opportunities, wellbeing, aesthetic values, and biodiversity. 

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This approach can be included in the Flood risk Management Plans that are required by the EU Floods Directive. WSUD can also contribute to the successful implementation of the measures set in the river basin management plans according to the EU Water Framework Directive, encouraging the sustainable management and protection of freshwater resources.  

Stormwater management can also be included in national legislation within specific acts related to land use and buildings codes. For example, requirements for stormwater management are stipulated in the Land Use and Building Act in Finland.  

Moreover, water management strategies set at local level are key elements that can provide strategic context to the implementation of WSUD. 

WSUD is a broad area of practice that includes very heterogeneous adaptation measures with a wide range of technical solutions. Therefore implementation time varies greatly, mainly depending on the scope and the size of the initiative. Very small scale WSUD practices at a single building level can be implemented in few months while large scale implementation that involve a neighbourhood or even an entire city can take several years. 

Practices implemented regardless of the spatial scale (technical solution in a single building or large integrated solutions at the neighbourhood scale) are generally long lasting (> 10-30 years) but they usually require regular maintenance otherwise their capacity can significantly decrease or the system’s function can fail.