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Policy on open stormwater in Oslo - a game changer

Submitted by Ase Johannessen 26th November 2021 14:44
Rain Garden Oslo


Surface water is one of the major challenges for all municipalities with cities or fairly dense and urban buildings. Surface water management is increasingly important in all spatial planning. Much due to climate change, but also because ever-increasing development entails a larger proportion of dense surfaces and thus greater runoff.

Oslo municipality has adopted a strategy on surface water management for 2013-2030. 

Common goals for the city is needed

The specific goals are described in p 5 of the strategy document:

  • Meeting the climate challenges and minimizing damage and inconvenience means that «damage as a result of surface water and urban floods must be avoided». Then we must, for example, have good knowledge of the water's path through the city, have identified and adapted flood roads and diversion areas, and good preparedness.

  • Taking care of the environment and securing the water bodies means that «all surface water supplied to a recipient must have quality which the recipient can tolerate so that the objectives of the water regulations are achieved». Then we must, for example, limit pollution from surface water from roads, parking lots and construction activities, and we must open as many stream closures as possible.

  • Using surface water as a resource means that «surface water must be infiltrated, delayed, and used locally where it is practically possible, and that we use open, natural and multifunctional diversion systems». Then we have to for example, make it easier to choose these solutions over traditional ones, and the municipality must take the lead with a good example.

The city of Oslo is promoting open stormwater drainage.

"We will use open and multifunctional surface water solutions"

p 7: Adapting surface water management to more challenging weather requires that we free ourselves from thought that all water should be in pipes. The surface water must be taken care of in the local environment, or in your own garden instead to take up space in the drainage system. At the same time the water becomes easier to handle when the extreme weather come, open and multifunctional solutions will bring both aesthetics and life back to the city. Natural slowing down of water through more extensive use of green areas reduces the risk of flooding. 

The city is following a three step strategy: 

1. When it rains a little, we reduce the risk of flood and ensures better water balance by using more green; such as trees, rain beds, green roofs and permeable surfaces instead of asphalt. We can lead surface water from roofs, roads and open spaces to green areas, open ditches and canals or to a water body.

2. If it rains a little more then we have to collect and hold back surface water by dedicating areas for diversion and make sure the areas are equipped for take care of the surface water. We must reduce the risk there where surface water often accumulates and leads to floods and damage, and where a flood is critical.

3. When the extreme weather comes, we must also lead surface water safely to the fjord by facilitating dedicated flood roads, i.e. some roads and watercourses, and ensure that the surface water is channelled safely to the flood roads and further in the flood roads towards the fjord. In some places we may need to create systems below the ground as well.

Surface water should be a natural part of early planning

Surface water when we build new
Open and multifunctional surface water solutions must be planned. Some need a lot of space, but with a little creativity, it is possible to get good solutions less space too. The most important thing we can do is to take in surface water management as an equally natural part of the planning process, such as the establishment of roads and other infrastructure. It will make it easier and more predictable in later processes, such as the construction case.

Surface water in existing buildings
When we build new, we have all the possibilities. The majority of the city, however, is already built and we have large challenges related to surface water management in it existing buildings. We need to make plans for how we can solve, or improve the surface water challenges in these areas.
This means which solutions we can establish where, how we can implement them and who needs to do what. Oslo Municipality itself must do something, however at the same time, the individual landowner must also do something improvements (such as taking care of surface water from the roof on their own property).

Cheaper to prevent than to pay damages

Relocating surface water management in Oslo is a long-term and costly measure. Some measures, such as laying about the solutions and facilitate flood management in existing buildings can be very expensive, while others do not necessarily have to cost that much. At the same time, the costs of damage that surface water can inflict in these areas is already a lot, and it is very probable that the cost will increase significantly in the years to come.

It will therefore be more socially beneficial to pay for preventive measures that at the same time add value to the city and gives the municipality a good reputation, than to calculate with large claims payments.

We have to share the costs

When we start preparing an action plan, we must first of all review the costs that the measures lead to, and what resources they will require.

To take care of surface water is not something an agency can succeed on its own. Surface water is a shared responsibility and close and good interaction across issues is required. This means that more people must join and pay for the measures.

The water and sewerage fees can pay for measures that can directly linked to the relief of the sewer network, while measures which goes more in the direction of facilitating green areas probably have to be paid for by other agencies' budgets. How far we can go in using the water and sewer charges to climate adaptation measures is still unclear.

Private developers and landowners must also expect costs associated with managing surface water on your own superficial. The majority of the measures we must take will be one part of the already planned development.

The Water and Sewerage Authority shall have sector responsibility
for surface water

The Water and Sewerage Authority shall have the City of Oslo sector responsibility for surface water. One of the most important tasks the agency must solve is to coordinate the surface water work in the municipality, and take care that the holistic perspective is taken into account when planning surface water solutions. At the same time, the agency must be able to provide guidance and information for the municipality's businesses in their own surface water work, but also to architects, developers and others when planning sites. As the sector manager, the Water and Sewerage Authority must ensure that ownership of all the tasks that must be solved. The sector manager must also ensure that we get all instruments in place we need to carry out the tasks.

What is the role of "all the others"?

The fact that the Water and Sewerage Authority is responsible for the surface water aspect for the municipality does not exempt the other municipalities the enterprises, the private enterprises (developers, contractors, architects, etc.), nor the inhabitants of Oslo for an independent responsibility. We all have a responsibility to ensure that the surface water is taken care of in a safe and good way and that municipality, we must «sweep for our own door».

The municipal enterprises must ensure that they take safe care of the surface water within their areas of responsibility. At the same time, they must follow the municipality's principles and strategies for surface water management, so that the entire municipality works together on improved surface water management in the city.

The private companies must make sure that they include the surface water management when planning areas, and sets aside plenty of space to take care of the surface water on the site itself. They must also make sure that the solutions they choose does not lead to injuries to neighbors.

Oslo residents must make sure that they take care of the surface water from their property without it leading to damage to the neighbor.


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