Just like many other towns and cities, Apeldoorn suffers from flooding during extreme rainfall. The Municipality of Apeldoorn has therefore disconnected the rainwater from the sewer system with the help of 150 DSI® infiltration wells. It is a pilot project that the entire of Europe could learn lessons from.
Collaboration and monitoring
Solutions for the draining off and infiltration of rainwater in Apeldoorn are being funded from the EU’s LIFE programme. The project is therefore called LIFE project AERFIT (Adaptation to Extreme Rainfall). The Municipality of Apeldoorn is collaborating on this project with Henk van Tongeren Water & Techniek, Stichting 02DIT, STOWA-Stichting RIONED and Hölscher Wasserbau. Once the wells have been constructed, they will be monitored for two years. The results will ensure that the DSI® technique can be further developed and improved.
Between 2019 and 2022, wells will be constructed at various locations in the municipality. To minimise the inconvenience to the public, the construction of wells will be combined as much as possible with other jobs, such as replacing parts of the sewer system or the road surface. In 2020, Henk van Tongeren Water & Techniek placed 20 new DSI® wells in Apeldoorn. For 2021, 50 new wells are planned.
When selecting locations for the DSI® infiltration wells, it needs to be determined whether the soil is permeable enough. That determination has to be very precise. Even a slightly higher clay level can slow down the infiltration by 40%. The depth of the filter also plays a role. As a consequence, when a well is drilled, a soil profile is first of all made. In this overview, the composition of the soil at each depth is listed: does it contain more clay or more sand, and how much gravel is there? The filter is subsequently placed at the level of a well-drained layer.
A previous pilot in Putten revealed that the filters of the DSI® infiltration wells regularly become blocked due to organic matter. Therefore, new filters are being used in Apeldoorn. The new filter consists of an inner and outer filter. The inner filter can easily be brought to the surface to clean. That ensures a better functionality at lower maintenance costs.
The first experiences with the DSI® infiltration wells in Apeldoorn were positive. There was less flooding in 2020 despite the heavy rainfall that year. In the coming years, the function of the wells during downpours will be further monitored.