Slot drainage channel in Elburg combats waterlogging
In the fortified town of Elburg, severe downpours can cause waterlogging. To prevent this, the municipality decided to redevelop the city centre. The authorities sought a climate-proof system for rainwater retention and drainage. As the old surface relief was rather uncomfortable for both cyclists and pedestrians, the new drainage system was combined with new pavement.
How has the municipality arrived at a redevelopment plan?
A project support group was set up for the redevelopment of the town centre. This group represented a wide range of stakeholders, such as residents, shopkeepers, the catering industry, the tourism sector, and the archaeological society. Following intensive preparations, this group presented a plan comprising adaptation of the town centre pavement and the construction of a slot drainage channel: a roadside gutter to drain rainwater. The municipality assessed the plan and elaborated it into a technical drawing, factoring in ways to adapt the town centre to the impact of climate change.
What adaptation measures have been implemented?
An ACO Q-max slot drainage channel has been installed that drains rainwater to the brook which crosses the town. The brook flows into the Vestinggracht canal. The slot drainage channel prevents rainwater from ending up in the sewer system. Private downspouts have also been disconnected from the sewer system. Furthermore, Vischpoortstraat and Jufferenstraat streets have been repaved: rainwater now runs off to the roadside, ending up in the slot drainage channel. As the rainwater eventually ends up in the Vestinggracht canal, the slot drainage channel also contributes to the cooling of the town centre. The authorities are planning to construct a cooling island here, featuring lots of greenery, trees, seating areas, and a water tap. As the slot drainage channel helps to retain water in the canal, this measure will also be conducive to combating drought.
Why has the municipality opted for a slot drainage channel?
A slot drainage channel is slightly more expensive than storm drains and separate stormwater flows, but far easier to install. It does not require pipes and can be connected directly to the urban canal. Furthermore, unlike storm drains, a slot drainage channel does not require cutting openings for water to run off. Another convenient feature of the slot drainage channel is that it can be installed on top of the Vitens water pipes, thus reducing the excavation depth for the contractor. This also eliminated the risk of encountering archaeological finds, which would have delayed the construction. Finally, the slot drainage channel is hardly noticeable in the street aesthetic and easy to clean.
How efficient is the slot drainage channel in combating waterlogging?
The ACO system is capable of draining category 10 downpours: downpours involving 35.7 millimetres of precipitation in one hour. Experience will have to show whether the measure is effective. If the volume of rainwater exceeds the drainage capacity of the system, excess water will run off above-ground to the brook.
Ideal solution under pressure of time
The job seemed simple but was not. Time was the main enemy. The contractor – Van Gelder – commenced on the project in January 2021. As the tourism season always starts at Easter, the redevelopment was scheduled to be completed by that time. This shallow slot drainage channel was the ideal solution because it eliminated the risk of delays as a result of archaeological finds or pipe crossings.
Lessons to be learned
Wherever possible, the municipality of Elburg involved local residents in the process. This boosted public support for the project. Another choice that worked out well was the construction team contract format: the contractor was involved in the planning process as early as the design phase. This has the advantage of identifying and being able to address risks at an early stage. This project was a fine example of efficient collaboration between the private sector and the government.