Stormwater inlet in street

Two concepts in urban storm water management

By Johanna Sörensen (, Water Resources Engineering, Lund University

In this article, two concepts in urban storm water management, the Three Point Approach (3PA) and Sustainable Urban Drainage System (SUDS), are presented and discussed. While SUDS is well known and has been used for many years, the 3PA is new and not so well documented. SUDS could be called a Best Management Practice (BMP), while 3PA is a tool for discussing urban storm water management.

According to IPCC (2007) it is “very likely that … heavy precipitation events will become more frequent” in the future (during the 21th century) because of climate change. The expected life time of a conventional urban drainage system is 50-100 years (Winther, 2011) and consequently it is important to consider climate change effects in all urban storm management, even though the precise effect are uncertain. The uncertainty calls for a more resilient design (Godschalk, D. R., 2003).

Three point approach, 3PA

Frantini et al. (2012) have developed the Three Point Approach (3PA), which is a tool for urban flood risk management. The idea is to give managers and operators a tool for discussion and reflection when planning a new drainage system or redesigning an old system. The three points are presented as follows:

  1. Domain of technical optimisation: This is the domain for design storms, which are typically described by national guidelines. In this domain, system optimisation from a socioeconomic perspective is discussed. The idea of national guidelines is often to prevent cities from storm floods to occur more often than with 2-20 years return period.
  2. Domain of urban resilience and spatial planning: Bigger storms, with return periods higher than 2-20 years, will occur and therefore city needs to be resilient toward flood risk from such event.
  3. Domain of day-to-day values: When building a resilient city, as mentioned in point 2, big above ground areas are often needed. These areas should be useful also in the daily life for people in the city, which calls for an inclusion of social participation. The political and public participation is also important for the public awareness of flood risk.

Sustainable Urban Drainage System, SUDS

Urban drainage systems are built to transport waste water from households and industries to treatment plants, to drain and to prevent cities from being flooded. But, there are three major problems connected to urban drainage: pollution from Combined Sewage Overflow (CSO) and from paving, roofs, etc., high peak flows causing erosion in receiving waters and flooding when the system is overloaded. These problems calls for better design and many authors suggest Sustainable Urban Drainage System (SUDS) as a solution. Poleto (2010) presents the following goals for SUDS:

  • Quantitative control of surface runoff;
  • Improvement in the quality of water from surface runoff;
  • Conservation of natural characteristics of bodies of water;
  • Balance of hydrological variables in watersheds.

Another goal with SUDS is to achieve a more resilient urban drainage system, as the SUDS solutions are more flexible than using a conventional pipe system only.

In many cities today, we are spending a lot of money on transportation and treatment of storm water. In combined systems the storm water are often pumped a couple of times before reaching the waste water treatment plant, WWTP. The WWTPs need a huge extra capacity to be able to take care of the water load from heavy rainfall. During the rainfall, treatment processes will run in an inefficient way because of the extra load. When the limit of the WWTP and the sewage system is reached, combined sewage overflows causes pollution in the receiving waters. In separated system the storm water are often led directly to receiving waters, without any treatment. Therefore a separated system is not good enough to solve problems with heavy metals in lakes, etc. According to Berndtsson & Bengtsson (2006a, 2006b, 2007) storm water from urban areas is the highest contributor for heavy metals to smaller rivers. Therefore also storm water needs to be treated, for example in such a storm water treatment facilities as described in Vollertsen et al. (2007).

Another problem, caused by building more impermeable surfaces in the cities, is that the water cannot reach the ground water to the same extent as in natural systems. This has an effect on the water supplies where ground water is used as drinking water. In addition to this, the pollution from the cities lowers the possibility to use ground water as drinking water (Winther 2011).

Poleto (2010) suggests following types of techniques for sustainable urban drainage:

  • Permeable pavement;
  • Semipermeable pavement;
  • Detention and retention reservoirs;
  • Infiltration trenches;
  • Infiltration gullies;
  • Infiltration wells;
  • Microreservoirs;
  • Rooftop reservoirs;
  • Green roofing;
  • Underground reservoirs; and,
  • Grassed strips.

Many of the suggested techniques above are both treating the water by sorption or degradation of pollutants and delaying the water flow and thereby minimising risk for erosion and flooding. While the permeable pavements only are effective until infiltration capacity is reached, they can be combined with other uses, like being used as a school yard or a parking lot. Infiltration trenches can successfully be combined with many other functions as they are built underground, if the hydraulic capacity of the soil is big enough. But they share one problem with conventional pipe systems; they are not flexible in their design. Green roofs are only effective for smaller rain falls, but they are useful for many other tasks, like energy saving and making solar power more efficient by lowering the temperature in cities/on the building, obtaining noise reduction, isolating buildings, providing richer ecosystems to the cities and helping degradation of air pollutants (Berndtsson 2010). Green roofs have also a big effect in lowering the annual runoff by evapotranspiration (Berndtsson 2010). Different kinds of reservoirs are very effective, but needs big areas for construction. However they can often be combined with other uses, in the same way as permeable areas. Grass areas in parks can be used as storm water reservoir while raining and as a recreational area in sunny days.

One SUDS technique not mentioned in the list above from Poleto (2010) is the synthetic wetlands used for instance in Malmö, Sweden (Stahre, 2006). This technique is very effective, both for flood control, detention and remediation, if the required area are present.


We are facing a climate change, which means that we can expect more extreme weather, including more extreme rain fall. The investments for adaption to more heavy rainfalls are huge. As we would like to develop our cities to more liveable places, we need to cleverly use every penny two times: both for storm water control and for other things such as for recreation, better ecosystems in our cities, energy saving and so on. The Three Point Approach helps us to discuss the different needs in a systematic and holistic way.

One thing that Frantini et al. (2012) do not mention is the importance of taking care of pollution from storm water and sewage system. The focus in Frantini et al. (2012) is on flood risk. I suggest that the third point, day-by-day values, in an extended version of the 3PA also should include also the pollution problem. By discussing pollution as a part of the day-to-day values domain, a more sustainable system would probably be built. A slow runoff is important for both degradation of pollutants and a more controlled outflow to receiving waters. In a combined system a slow runoff would secure better remediation at the treatment plant and fewer sewage overflows.

I have tried to find literature on two other subjects of interest, by searching in online libraries and talking to professors and practitioners in urban storm water planning. I have found little concerning the following questions and I would therefore suggest further research in these areas:

  • Catchment effects from SUDS – how is the downstream system effected by implementation of Sustainable Urban Drainage System in one part of the city? Is it needed to reconstruct the drainage system of the whole city to have a well functioning system, meeting climate change in the future? Or is it enough to reconstruct and develop SUDS in only some parts of the city?
  • SUDS effect on extreme events – can SUDS protect against flooding from extreme events (point 2 in the three point approach)? Or is a conventional pipe system with large basins needed in addition?


Note that this text was written in December 2012. For instance, I have published a paper on how SUDS affect flooding during extreme events. However, I still find it relevant and hereby publish the text for anyone to read.


Berndtsson, J. C. & Bengtsson, L. (2006a) Vattenöversikt i tre skånska åar, VA-forsk rapport nr 2006-22

Berndtsson, J. C. & Bengtsson, L. (2006b) Stadens inverkan på vattenmiljön i avrinningsområden, VA-forsk rapport nr 2006-23

Berndtsson, J. C. & Bengtsson, L. (2007) Vattenöversikt i små avrinningsområden i Skåne, VATTEN-3-07

Berndtsson, J. C. (2010) Green roof performance towards management of runoff water quantity and quality: A review, Ecological Engineering, Volume 36, Issue 4, April 2010, Pages 351–360

IPCC (2007) Climate Change 2007: Synthesis Report: An Assessment of the Intergovernmental Panel on Climate Change

Frantini et al. (2012) Three points approach (3PA) for urban flood risk management: A tool to support climate change adaptation through transdisciplinary and multifunctionality, Urban Water Journal 2012, 1-15

Stahre, P. (2006) Sustainable in urban storm drainage, Svenskt Vatten, ISBN 91-85159-20-4

Vollertsen et al. (2007) Treatment of urban and highway stormwater runoff for dissolved and colloidal pollutants, conference paper, Novatech’2007

Winther L. et al. (2011) Afløbsteknik 6. udgave, Polyteknisk Forlag, ISBN 978-87-502-1015-3

Godschalk, D. R., (2003) Urban Hazard Mitigation: Creating Resilient Cities, Nat. Hazards Rev. 2003.4:136-143

Vad Malmö behöver är ingen avloppstunnel

Rainy day in Lund

Vilken väg ska vi välja?

Idag skriver Sydsvenskan att avloppstunneln i Malmö, som VA Syd har föreslagit, beräknas kosta 2 miljarder kronor. Det är mer än vad Malmö Live, Malmös nya konferens-, hotell- och koncerthus, kostade. Det är vansinnigt att gå den vägen och plöja ner så mycket pengar på en statisk och kortsiktig lösning när Malmö är världskänt för att arbeta med betydligt modernare metoder.

Vad Malmö stad minst av allt behöver är att gräva ner 2 miljarder under jord. Satsa på mer grönt och blått i staden istället. Det ger minskade föroreningar (luft och vatten), lägre risk för översvämning och högre biodiversitet. Om vi arbetar med blå-gröna lösningar kan vi samtidigt se till att skolgårdar, parker och bostadsområden blir trevligare och roligare att vara i. Det finns många ställen i Malmö som skulle kunna rustas upp och samtidigt bli en del av ett blå-grönt nätverk genom staden.

En tunnel kan endast lösa en fråga: minskade föroreningar i vattnet. Modern VA-teknik har kommit betydligt längre än så. Vi måste använda pengarna bättre och lösa flera frågor samtidigt. Inom akademin idag är två honnörsord multifunktionalism och resiliens. Multifunktionalism betyder att en lösning ska ha många funktioner på samma gång, så vi får ut så mycket som möjligt av varje spenderad krona och varje bit mark vi bygger på. Resiliens betyder bland annat att vi ska vara beredda på framtida förändringar. Därför måste vår stad och all infrastruktur vara flexibel, så att den kan förändras när staden eller klimatet förändras. Tunneln som VA Syd har skissat på tycks vara allt annat än flexibel. Det vore bra om VA Syd berättade hur de tänkt sig att tunneln ska kunna förändras i framtiden och vad det i så fall skulle kosta att bygga om den.

Sydsvenskans har skrivit en för- och emot-lista för tunnelbygget. Listan ger en hyfsat bra bild av frågan, men de nämner inte ens blå-gröna lösningar som ett alternativ, trots att Malmö är världskänt för just detta. Där kan vi prata beprövad teknik.

I VA Syds utredning nämns att “.. de gröna och blå kvaliteterna ska utvecklas. Malmös parker, grönområden och vattenmiljöer ska utökas, värnas och ha höga rekreativa och biologiska kvaliteter.” Trots det föreslås alltså en tunneln, vilken inte direkt bidrar till höga rekreativa och biologiska kvaliteter. Om hållbar dagvattenhantering (blå-gröna lösningar) skriver de att “.. denna typ av åtgärder kan vara mycket effektiv för att minska risken för källaröversämningar och generellt bidra till att toppflöden i ledningsnätet minskas.” Trots det har de inte beräknat vad lösningen kostar och hur mycket staden tjänar på att förbättra både rekreativa och biologiska värden. De nämner ytterligare tre möjliga lösningar, men inte heller här några beräkningar av plus/minus för ekonomi, samhälle och miljö gjorts. Om vi ska kunna ha en förnuftig debatt kring detta, krävs att alternativen utreds lika noga som tunnelförslaget. En utredare med uppgift att se till hela stadens intresse, måste studera detta i detalj. På åtta år och med 2 miljarder i budgeten kan Malmö genomföra många projekt som förbättrar både vattenkvaliteten och staden som helhet. Tänk så många områden som skulle behöva förbättras ordentligt och vilka möjligheter en så stor budget ger. Och samtidigt slipper man sitta fast i ett statiskt och oflexibelt system.

Malmö behöver förmodligen ingen avloppstunnel när det nu finns väl beprövade, bättre alternativ – men om vi ska kunna diskutera frågan krävs det att alternativen utreds ordentligt av en utredare som ombeds att se på staden som helhet. Förmodligen behövs en grupp av experter från olika discipliner, eftersom modern avloppsteknik involverar många olika frågeställningar och går på tvärs av staden både fysiskt och organisatoriskt.

Development of stormwater systems

I am very thankful to ÅForsk, who gave me the opportunity to go to the International Conference on Flood Resilience (ICFR) in Exeter, Great Britain. I am also glad that my paper about the storm water systems in Gothenburg and Mumbai got accepted to be presented at the conference. It gave me a great chance to dig deep into the development history of the stormwater system in Gothenburg. Arun Rana and I made a comparison between the Gothenburg system and the stormwater system in Mumbai and learned a lot from reading about how the systems have developed.

Stormwater inlet in street

Stormwater inlet in street

The sewer system of yesterday strongly influences the system of today and thereby also the system of tomorrow. Because stormwater and sewage structures last for a long time, and the price to reconstruct the systems are very high, the old system will have strong influence on all future decisions. Cettner, Söderholm and Viklander (2012) did write an interesting article about this in Journal of Urban Technology. This was one of the important learnings from the article writing and my conference preparation.

Conference lunch at ICFR in Exeter

Conference lunch at ICFR in Exeter
Photo: Johanna Sörensen

At the conference, I enjoyed to meet peers from all different universities, working with flood related issues in European and Asian cities. We discussed how the urbanisation and city development affect flood risk in growing cities and how climate change can aggravate the risk. We discussed how to cope with the flood risk, both from a technical and a social point of view. How far can we come with technology? What are the possibilities to protect our cities from floods? Flooding is one of the most wide-spread disasters, which can hit cities in various climates all over the world. A big concern for the future is the rising sea level, due to heating of the globe. In addition to rising sea level, we will also see more high-intense storms in many places. How can we construct our cities in a smart way to handle this? The main idea from the conference, which I took with me home, was that we will not be able to totally avoid flooding. When cities are hit by the most extreme events, there will be floods of such a magnitude that we cannot prevent them. Therefore, we need to build cities in a resilient way, with flexible systems, flexible public organisations, and flexible citizens that are prepared to cope with floods. A big flood event must not be a catastrophe for the city if the preparation is good and the technology is adaptable.

The conference gave me a complete view of ongoing flooding research. There are four main driving forces behind severe pluvial flooding in cities today: higher precipitation due to climate change, urbanisation, land use change, and higher sea level due to climate change, which can aggravate pluvial flooding. In some parts of the world, only one or the other driving force is seen, but in many places are several of these processes ongoing.

Comparison between stormwater system in Gothenburg and in Mumbai

There are several similarities between the stormwater system in Gothenburg and in Mumbai. Both systems where constructed in the late 19th century with strong influences from Great Britain. India was at the time under British control and the British engineers led important infrastructure projects in Mumbai, among those building of the early sewer system. In Gothenburg, Swedish engineers went to London to learn about the new technology and were in this way strongly influenced by the British engineers. Later on, the German engineers led the technological development in this field in Europe. Today the systems in the two cities are very different, despite the fact that the first parts where built in the same time and in the same way. After the British Empire left India, the infrastructural development of Mumbai stagnated. Things have happened since then, but at a slower pace compare to Gothenburg, were the development continued. Also the urbanisation has been considerably stronger in Mumbai, which is the biggest centre for trade and commerce in India.

Solid waste in stormwater system in Mumbai

Solid waste in stormwater system in Mumbai.

It is obvious that the problems related to flooding are much bigger in Mumbai, compared to Gothenburg. The monsoon period comes every year with heavy rainfall and the stormwater system does not have capacity enough to handle the runoff. The solid waste system in the city is not satisfactory, meaning a lot of plastic bags with solid waste lie in the watercourses instead of landfills and cause clogging of the stormwater system during the monsoon period. The municipality aims to clean all watercourses before monsoon, but often the jobs is not done careful enough to keep the watercourses free from clogging. Therefore, a better solid waste system is very important to improve flood control in Mumbai. Another problem in Mumbai is settlements on flood plains along the river. Many people in Mumbai are very poor and the city is overloaded with people. Because there is no housing for all people in Mumbai, many informal settlements are built on the floodplain and people of the floodplain lives in a high risk of flooding. As this is the poorest people in the city, they also have least possibility to protect themselves.

The ship Götheborg in Gothenburg harbour.

The ship Götheborg in Gothenburg harbour. Götheborg is a copy of a 18th century ship.
Photo: Mikael Tigerström.

One similarity between Mumbai and Gothenburg is that both cities were built on former marshland along the coast. Both cities were built as an important port and economical centre for their region. They are both low-laying and situated close to the sea, meaning the water cannot easily leave the area during storm. Gothenburg is known as one of the rainiest cities in Sweden, while Mumbai is situated in an area with monsoon climate. Both Gothenburg and Mumbai lay on the west coast with mainly westerly winds, meaning they are influenced by the sea.

Mölndal River

Mölndal River at Lackarebäcksmotet.
Photo: Johan Jonsson.

In Gothenburg the area around the central station, Gullbergsvass, is low-laying and in high risk of getting flooded. There are far-reaching plans to develop this area into a housing and shopping area in the future, despite the high flood risk from Mölndal River. When it comes to flooding, this is one of the main problems in Gothenburg, together with rising sea level and landslides along Göta River. When reading about this, I learned that high risk of flooding not always is enough argument to leave an area free from expensive investments.


Cettner, A., Söderholm, K., and Viklander, M. (2012) An Adaptive Stormwater Culture? Historical Perspectives on the Status of Stormwater within the Swedish Urban Water System. Journal of Urban Technology, 19(3), 25–40.

Toaletter på Jane Austens tid

Jag håller på att skriva en artikel om avloppsteknikens utveckling i Göteborg. Under detta spännande arbete, som jag hoppas kunna skriva mer om, har jag också blivit nyfiken på utvecklingen i England och föll därför över en artikel/blogg om toaletter på Jane Austens tid. Göteborgs avloppssystem, som kom på dagordningen under 1850-talet, var nämligen inspirerat av avloppssystem i engelska städer, vilket gör de engelska systemen extra intressanta för mig. I Sverige saknades kunskap, men efter flera studieresor till England kunde planer för byggnad av avloppssystem i Göteborg skrivas. Det är intressant att tänka sig att vi inte har haft vattenburna toaletter i mer än cirka 100 år. Förhållandena i Sverige såväl som i England var vidriga i städerna, med stinkande avloppsvatten på gator och bakgårdar.

Jag kan inte låta bli att visa denna fina bild som artikeln ovan länkar till. En kvinna hämtar vatten från en kran alldeles bredvid en radda soptunnor. Hygienen är förmodligen inte den bästa och detta är ändå långt senare än 1850-talet, nämligen 1931.

Kvinna hämtar vatten vid vägen, med soptunnor i bakgrunden längs väggen.

Kvinna hämtar vatten. Lägg märke till soptunnorna i bakgrunden som potentiella smittospridare. Bilden är från 1931.

Jag återkommer med mer om Göteborgs avloppssystems historia – det är något att se fram emot!