Climate adaptation and rainwater management at the surface

Increasing rainfall means that it will be difficult to meet the service level specified in the wastewater plan and observe the terms and conditions of the discharge authorisation of the wastewater treatment plants. Pipe capacity is already too small in many places, with excess water - a hazardous mixture of wastewater and rainwater - flowing into lakes, streams or the Bay of Aarhus untreated. The excess water also causes flooding of cellars, roads and green areas. In other words, we lack space in our sewer system, and at Aarhus Vand, we are doing something about this - in close cooperation with the municipality of Aarhus.

In Aarhus like in many other municipalities, we are hard at work on separating rainwater and wastewater in areas where this has not already been done. In some of these areas, rainwater is lead through new pipes. In other areas, we handle rainwater at ground level or through a combination of both methods.

In our attempt to adapt our city to climate change and avoid damage to properties or infrastructure following heavy rain, we treat everyday rain and 5-year rain events on the road surface and/or in drains. We do so because there is a potential for separating large areas for the same amount that it would cost to lay pipes. In addition, it offers a unique opportunity to use rainwater in a new way - for embellishment and recreational purposes. We make rainwater a visible element in the form of rainwater lakes, rainwater beds and rainwater drains. We also establish hollows and dams; we create entirely new urban spaces and find new ways to lay out green areas. The municipality of Aarhus has a vision of making Aarhus an even more attractive place to live, and Aarhus Vand should help support this ambition with our climate adaptation projects on the separation of rainwater and wastewater.

In Risvangen, Aarhus, rainwater is handled through a combination of surface handling and pipes. Whether we choose to lead rainwater through new pipes to a stream or handle it on the terrain, we develop and prepare our sewer system for heavy rain - a direct consequence of climate change. Our choice of solution always depends on the local conditions. Furthermore, we keep measuring our efforts against the risk of flooding and the cost of the damage caused by flooding.

We've done it before

Aarhus Vand has carried out two major climate adaptation projects with rainwater being handled at the surface - one in Lystrup north of Aarhus and one in Risvangen in the northern end of Aarhus. In Lystrup all 12 climate adaptation solutions involved surface treatment. In Risvangen, rainwater is handled in a combination of surface handling and pipes. In both cases, vast resources were spent on citizen dialogue/involvement.

We become visible

At Aarhus Vand, we are faced with a new approach to rainwater treatment. Instead of two covers in the road, we establish visible water beds in the urban space in the form of rain beds, beds along roads, (wadis) and rainwater lakes. This gives rise to new expectations from citizens and landowners. We establish visible green drainage systems in the urban space. Since they are going to last for many years, we want them to add beauty to the urban space. This begs the question of what is beautiful/neat - a question to which there is no objective answer. It entails approaching the citizens who are going to live with these solutions to ask them what they think fits well into their area. This is no easy task. It is like asking people what good art is.

How do we succeed?

In addition to a new type of citizens involvement, this new reality calls for a new way of dealing with the stakeholders whom we often work together with: The road authorities the environmental authorities, road planners, urban planners, road operations, green upkeep, joint councils and homeowner’s associations. All very important stakeholders and key to our success.

In Risvangen, in Aarhus, rainwater is handled through a combination of surface handling and pipes.

Often there are other users who do not live in the area: kindergarten children, schoolchildren and the elderly. They also have to live with the new visible green drainage solutions. Therefore, it is just as important to get them involved and hear what they think. As a utility, we enter into a world in which citizen involvement processes become part of a drainage project.

The project manager will therefore contribute to a citizen process. We call it contributions, because as the manager of the climate adaptation and wastewater plan, it is the municipality of Aarhus who is responsible for carrying this process through. Success depends on close cooperation between municipality and utility. The municipality of Aarhus and the utility will see an increase in the entire information and citizen involvement efforts compared to earlier, and therefore the right resources must be allocated in order to succeed. We must make every effort to establish beautiful green solutions.

The added value of green drainage solutions may be further increased by integrating them with public benches, exercise tools and footpaths. However, this is not something the utility can finance. This is where the homeowners’ association and/or the municipality must pay, or where new sponsors must be found. This way, an active homeowners’ association or local council may prove to be important in ensuring a successful outcome.

Integration of rainwater beds - beds along roads with technical solutions to limit speed - is another example of added value creation. Either in combination with road bumps and/or split roadbeds. This must, of course, take place in close cooperation with the municipal road technicians, who must ultimately approve such projects.

A new reality—new challenges for the utility

Aarhus Vand may be said to be moving into unchartered territory, with the opportunities and risks this entails. We will inevitably make inappropriate solutions and even mistakes. Therefore, we must be prepared to fix the solutions we come up with. This could be in relation to a technical defect, say, a drain that does not works optimally. Where surface handling solutions are concerned, a drop that is merely a few centimetres off at the surface will cause the rainwater not to be led to the intended roadbed.

Citizens may also react to the plantation in which case we may have to make changes to our solutions. If the plantation is not maintained, then what? Do we then lose the support of the citizens?

In the long-term, cultivation and maintenance are very important aspects. What about roadbed plantation, rainwater drains or rainwater lakes? Who will maintain them and how? In Aarhus, the municipality is responsible for the upkeep of plantation, whereas the utility is responsible for the functionality. But what does that mean? Can operations and maintenance become a ticking bomb under the economy?

How do we register the new surface solutions? We know how to register rainwater pools, but what about roadbeds, drains, etc.?

How do we ensure that the laying of a new wearing surface or the establishment of new road bumps do not interfere with intended waterways, thereby obstructing the functionality of e.g. roadbeds or a climate adaptation solution?

What about private roads? And so on. The short answer is that we do not know. Therefore, it is important that we keep documenting the impact and the costs. We must learn along the way and we gladly share our experience with others.

Urban development

Aarhus is rapidly evolving, and the city is growing fast. Every year, 5,000 new citizens move to the municipality. This means an increasing demand for new housing. This demand will be met partly through urban densification, typically with high-rise building in the city centre, and partly through the establishment of new urban areas in the surrounding area with dense/low building. In the latter case, surface solutions may be introduced from the beginning. In Malling, a small town to the south of Aarhus, a new urban area has been planned to the south of the town, with the establishment of a drainage system for rainwater handling (everyday rain, 5-year rain events and cloudburst) based solely on a surface solution. It was the express will of the builder to go along with this solution, the rationale being better economy and the creation of added value to the area. For obvious reasons, citizen involvement has not been part of this project. From the very outset, the purchasers have known that this was about a different type of rain rainwater handling. The homeowners are responsible for the green maintenance whereas Aarhus Vand is responsible for the proper functioning. One of the challenges is whether the landowners manage to take the brunt of operations and maintenance. But if the outcome is successful, the perspective for future new urban areas is great.

Aarhus Vand in favour of surface solutions

There are many challenges to overcome in creating surface solutions in the form of visible drainage systems appearing as green features in the cityscape. At Aarhus Vand, we have taken up the challenge because we believe that handling of rainwater at the surface in the form of green solutions will provide significant added value to the citizens and support the municipality's vision of making the city a more attractive place to live. A good example of this is the Risvang project, where we separated rain and wastewater in a large area for less money compared to a pipe solution. And many of the residents have complimented us on having succeeded in creating great added value which makes it an even more attractive area to live in.