Extreme rainfall also falls more and more frequently in Sweden in summer. Hedemora, a town in a hilly landscape where rainwater has always found a natural path, is the first municipality in Sweden where the increasing flooding has been  overcome with a Rockflow rainwater buffer.

With the increase in building and surface hardening, the rainwater system with approximately 90 kilometres of pipes has been overloaded more often than not in recent years. Hedemora is located in the valley through which an important traffic route also runs, which cuts through the city. Underground, three sewage pipes come together below an important traffic intersection, ending in one sewage pipe which passes under the road.

Dutchman Michael Heijting, who previously worked as a contractor at Reimer Construction and Infrastructure in Almere (NL) and as a water level manager at the water board in Coevorden (NL), has been “Projektör” at Hedemora Energi for several years and, in that capacity, initiated this innovative project. He brought the Dutch way of thinking that led to a solution for the flooding.

The client was Hedemora Energi, which provides district heating in the area and is also responsible for data cabling, drinking water supply and the sewerage system.

Sweden rainproof

We’ve known for a long time in the Netherlands that you only move the problem if you transport the water with pipes. Retaining the rainwater for a while is the best solution when you have to handle large quantities of water. If you can then release it in a controlled manner, you can prevent problems in lower-lying locations. This way of thinking is new here in Sweden. The first reaction is always to make the pipes larger so that more water can pass through. But we cannot simply enlarge around 90 km of sewer pipe in the urban areas here, that would be much too expensive.


At the intersection in question, an apartment complex had previously been built on a remaining piece of green land, and a small rain water buffer had already been constructed. When a parking lot also had to be constructed, the contractor called to ask where he could connect the street gullies to the sewer.

This couldn’t be considered with a system that was already overloaded, so my advice was to construct a collection basin of about 15 m³ under the parking lot. I later realized, however, that it was an ideal place to arrange a larger storage area in the middle of the problem area, so that the other water could also be collected there. With that in mind, I started lobbying within our organisation.

Space reserved for expansion

The 1 metre high, 40 metre long and 15 metre wide buffer has a capacity of 594 m³. However, the required capacity wasn’t the main question when determining the dimensions, the financial elbow room was. “We started from the available budget. The buffer collects the water from one of the three pipes that meet at the intersection. We expect that the current 600 m³ will be sufficient to reduce the number of floods from three a year to one at most. We have reserved a budget to also be able to collect the water from the second pipeline in the future.

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Roy Janssen

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