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City of Riga: Recommendations on implementing sustainable stormwater management

7 September, 2020 - 10:53

Stormwater management in the Baltic Sea Region cities

Due to the climate change Baltic Sea Region (BSR) is facing more frequent and heavier rainfalls, most heavily affecting densely built and inhabited urban areas. Therefore, cities are in emerging need to deal with the common challenge of stormwater flooding – a challenge that may lead to environmental degradation, infrastructure damage, risks to human safety and other adverse impacts to urban environment. Such challenge is not easily answered as it requires a holistic, comprehensive, and knowledge-based approach to stormwater management.

With aim to better understand the baseline and other pre-conditions for setting up a sustainable stormwater management in the BSR from September 2019 until March 2020 a comprehensive survey on stormwater-related legal review was carried out in all ten BSR countries: eight EU Member States – Denmark, Estonia, Finland, Germany Latvia, Lithuania, Poland and Sweden, and two partner countries – Norway and Russia. In parallel, structured interviews were carried out in 22 medium and large-sized cities of the BSR, assessing their current progress with introduction of sustainable urban stormwater management governance and practices, implemented improvements, as well as needs and future development prospects.

Both surveys were carried out as part of the BSR WATER platform project where one of strategic goals is related to improvement of policy tools and incentives enabling the BSR cities to implement sustainable urban stormwater management. Such an approach ensures that policy recommendations for implementing sustainable urban stormwater management are based on accumulated knowledge and practices of those forerunner BSR cities that already have obtained good understanding and practical skills within the field.

Stormwater-related legislation review

In all BSR countries principles and tasks of stormwater management are included in the national level legislation, defining objectives related to flooding prevention and ensuring water quality. However, the level of detail differs on these matters, specifically regarding the degree of setting some restrictions on the national level. Surprisingly, almost a half of surveyed cities have indicated no local (municipal) regulations for stormwater management. Surveyed cities indicated that stormwater management is guided by national law regulating mainly the stormwater quality and flood protection while existing local regulations mainly concern industrial and traffic areas and construction sites, but no infiltration in high risk areas. In addition, majority of interviewed cities confirmed presence of a stormwater fee, either a connection fee, a fee per m3 of discharge (combined/separate), or a fee per m2 of surface area of a fee differentiated by the type of property.

Stormwater-related legal review ascertained that in the BSR none or not enough attention is paid to promotion of open, nature-based, on-source stormwater drainage and treatment solutions. Only in a few forerunning countries (e.g., Denmark, Germany, Sweden, Finland) national legislation provides detailed requirements for stormwater treatment, irrespective of the type of stormwater drainage system. BSR cities highlighted the importance of this topic in entire urban planning system – all interviewed cities admitted the need to implement integrated stormwater management and sustainable stormwater planning as urgent.   

Stormwater systems and their performance

What can be concluded from the interviews, most cities in the BSR currently have both combined and separated stormwater collection systems, a few have only combined system, a few more have only separated system. Only about a half of surveyed cities admitted that they strive for completely separated stormwater collection system, while a quarter of cities have not set such a goal.

Concerning the ownership and management of the stormwater collection system, most of the cities indicated that both municipal water-&-sewage company and municipality are involved in stormwater management. Most often water-&-sewage companies and municipalities both own and operate stormwater systems, in rare cases water utilities operate municipality’s owned system. In some cities pipe systems are owned and managed by the water-&-sewage company while open stormwater collection techniques incl. green infrastructures – by the municipality.

In relation to baseline assessment of the stormwater system the following trends can be observed:  about a half of surveyed cities have done baseline assessment of stormwater collection systems, only half of these have used hydrologic and hydraulic modelling to determine capacity of the system and flooding risks. Others have only assessed treatment quality, technical inspection, and institutional structures. Interviewed cities reported lack of capacity in existing system in terms of flooding, lack of space for expansion, as well as the need for more integrated and more efficient management structures. Those cities where the stormwater system is managed by the water-&-sewage company seem to do better in this respect. Many municipalities have indicated lack of knowledge about their stormwater system. As to stormwater sewer design, only about a third of surveyed cities indicated sewers being designed for an extreme storm event – either in all city territory or in newly developed areas. A typical return period of the design event is mostly 10 years, in a few cases – 25 years. Differences exist on the exact technical specification of the return period: gravity flow vs pressurised flow. Also, a concern has been expressed about densely built areas, where sewers are being built because it is difficult to provide space for on-site sustainable urban drainage systems (SUDS). However, most of cities indicated, that thy are already applying on-site sustainable urban drainage systems (SUDS), however the sustainable techniques are not so widespread yet, as the most of these cities have only implemented their first pilots. Only a few forerunner cities apply them on a widespread basis as a common practice to improve water quality and overall urban space quality of the city.

Some general trends could be seen concerning the stormwater treatment. About a half of surveyed cities have indicated separate treatment of highly contaminated stormwater lead to wastewater treatment plants (WWTP), however different cities meant different sources of contaminated stormwater, from roadside stormwater receivers to special facilities. Most often urban stormwaters collected from industrial areas are treated and it is done in special stormwater treatment facilities. The treatment of street stormwater is still a big challenge in most of the cities.

Stormwater management practices and future needs

Concerning the current state in stormwater management in the BSR cities, only about a half of cities have some kind of local (municipal) climate adaptation plans in place, however some other cities are currently elaborating them. A few pioneering cities like Copenhagen, Helsinki and Vaxjo have elaborated and adopted comprehensive multi-sectoral plans looking at risks, impacts and measures across entire spectrum, incl. stormwater and green infrastructures as an integral part, while the other interviewed cities have more sectorial and less comprehensive approaches.

As to current practices in stormwater management, surveys highlighted such key issues as low priority of stormwater management in political agendas of vast majority of cities, lack of collaboration among different stormwater-related municipal departments and other relevant stakeholders, lack of knowledge, difficulties in retrofitting existing stormwater collection systems to new stormwater management approaches in terms of space and access, and other issues. Further, as the main challenges to stormwater management cities have indicated lack of quality control systems for dense urban areas in terms of stormwater management – e.g., lack of systemic water quality monitoring, poor water quality, foul connections, a need to disconnect properties from the combined stormwater collection system. Ultimately, the insufficient finance for stormwater management was indicated by all surveyed cities.

As a general reported obstacle to introduction of integrated stormwater management (ISWM) is a lack of resources and knowledge since environmental engineering is not a core competence of municipal specialists involved in urban planning. The ISWM is a becoming and a prevailing paradigm in stormwater management and almost a half of surveyed municipalities have adopted the decision to develop the ISWM as well as have defined their vision, objectives and expectations for their ISWM. About third of surveyed cities already have established cross-departmental teams of municipal specialists dealing with stormwater issues.

Most cities indicated that more knowledge and capacity building is needed to develop their ISWM – mostly on design, construction, maintenance and impact of SUDS and green infrastructure-based solutions, as well as on the modelling for integration of pipe systems with open stormwater collection systems and urban spaces.

In conclusion, surveyed cities identified the following issues as the most urgent to be dealt with: stormwater collection and treatment capacity in dense urban areas, availability of funding, cost efficiency, timely planning as well as ensuring water quality.

Summary conclusion

It was concluded that, in order to speed up introduction of ISWM at the EU level and in order to facilitate integrated solutions rather than single solutions focusing on just some aspects of stormwater management (such as water quality, flood protection, economic efficiency, etc.) more EU level guidance and incentives are needed. New policies shall promote and facilitate integrated solutions – development of liveable, comfortable, attractive, sustainable and resilient to climate change urban areas, combining spatial planning (e.g., sufficient green infrastructures, quality of green areas), sustainable mobility (e.g., green street design, green parking lots), energy efficiency (e.g., passive cooling design, green roofs and walls) climate neutrality (e.g., biodiversity, diversification of ecosystem services) and other aspects. In other words, a holistic, comprehensive approach is needed – planning, design and implementation of multi-functional and multi-benefit urban spaces fully capable of handling stormwater on site, including cost-benefit analyses demonstrating higher benefit-to-cost ratio of applied green infrastructures and nature-based solutions compared to conventional stormwater drainage solutions. Treating stormwater as a resource and economic sustainability of the ISWM can be facilitated by pricing the stormwater runoff. As EU leaves it to the member states to decide on cost recovery of stormwater management, further guidance or recommendations for stormwater tariff might be helpful.

What can be done on a city level?

For a city to be able to introduce an ISWM approach, the first step is to appoint a permanent local multi-sectorial consultative stormwater management group of municipal specialists dealing with integrated stormwater management. Such a group plays a crucial role in implementing sustainable stormwater management, as it directly supports introduction of well structured, integrated urban planning processes, as well as activates local experts for joint effort towards common stormwater-related goals. As the next step the city (municipality) need to elaborate and adopt a stormwater management programme or a plan, as part of city’s climate adaptation plan or self-standing policy document. Also, it is recommended to introduce building control tools, such as stormwater planning tools developed and piloted in the iWater project (e.g., Green Factor). Further, to support transition to sustainable stormwater management, cities need to elaborate or update local stormwater catchment basin plans and urban planning guidelines on decentralised sustainable stormwater management. Local (municipal) financial incentives to promote deployment of green infrastructures and nature-based solutions is another important city-scale policy tool to support development of natural, holistic, and sustainable stormwater management.


Nika Kotoviča
Riga City Council, City Development Department

Good to know

This article presents the report "Regional and national recommendations for integrated storm water management (ISWM)". This report is one of the key outputs of BSR WATER platform project, it is published in 2021.