Køge Municipality has established a 10,000 m² parking lot with permeable paving that can handle large amounts of rainwater in a short time.

Without expanding the existing rainwater system or establishing a basin, the parking lot can handle rainfall equivalent to a 10-year event. The permeable paving keeps the area free of water and drains the rainwater down into the base layer, delaying it further into the existing rainwater system.

No Wet Shoes for Students

Køge Municipality has invested in more educational facilities and attracts students from all over Zealand to Køge Campus, which offers over 50 different programs. The square meters are valuable in the campus area, which, in addition to the educational buildings, also includes newly constructed student housing and green spaces for the students. By developing the campus area, the municipality has taken up the challenge against cloudbursts and ensured that students never have to go to classes with wet shoes. As part of the campus area, the municipality has established Denmark's largest climate-secured parking lot with space for 300 cars.

Parking Area as a Delay Basin

The parking area can drain large cloudbursts due to its permeable base layer, consisting of 10,000 tons of DrænStabil® gravel, equivalent to 50 cm spread across the entire area. This layer acts as a delay basin and ensures that the volume of water from the parking area does not strain the existing rainwater system during rainfall, but flows through a water brake by gravity and onwards to the existing rainwater system. This climate-secured solution is the result of a collaboration between NCC Industry and IBF, who supplied the base layer and paving, respectively.

Protection of Groundwater

In Køge Municipality, groundwater is also extracted locally for drinking water and for the capital area. Therefore, a Bentonite membrane is placed under the permeable base layer to ensure that the infiltrating water from the parking lot does not seep down to the groundwater. In other cases, the membrane can be omitted, allowing the water to infiltrate fully.

Economic Benefits

Køge Municipality's own engineer, Ulrik Hinke Lindberg, a graduate civil engineer employed by the municipality as a road engineer, has led the way in choosing a permeable pavement for Køge Campus over a traditional pavement.

"We chose to install a permeable pavement for primarily two reasons. This solution eliminates the need to bury pipes under the site and also avoids the establishment and maintenance of a basin. A rainwater basin would occupy a significant amount of square meters, which we have instead been able to use for an additional building on the campus area. This is crucial in a place like this, where space is limited and square meters are expensive. So, actually, it hasn’t cost more to install the permeable pavement compared to a traditional one," explains Ulrik Hinke Lindberg, Road Engineer, Køge Municipality.

The parking lot can easily handle 230 l/s/ha (also known as a 10-year event) or what amounts to three cloudbursts. The pavement is designed so that water can rise up to the curbstones, about 10 cm above ground level. "But we probably won't see that for the next 100 years," says Ulrik Hinke Lindberg.

Maintenance and Operation of the Pavement

The establishment of a permeable paving area includes accounting for ongoing maintenance costs. A permeable pavement requires the joints to be cleaned with a special sweeping machine that removes the top 4 cm of DrænAf® gravel from the joint. The swept-up gravel removes at least 90% of the particle-bound harmful substances from car exhaust and oil. The collected material is recycled for asphalt production. The joints are refilled after cleaning with new DrænAf® gravel. Cleaning of the joints is only necessary when needed, which could be approximately every three years, depending on the surrounding vegetation. However, IBF has examples of pavements that have not been maintained for an extended period. In Sønderborg, IBF delivered a permeable pavement to car dealer Martin Iversen, which has not been cleaned since its establishment in 2013 and still drains rainwater from the parking area optimally. However, replacing the top joint material DrænAf® gravel also has aesthetic benefits.

Permeable Pavement at Køge Stadium

Elsewhere in the city, Køge Municipality has also used permeable pavements. In connection with the renovation of Køge Station, the municipality laid the parking area next to the stadium in permeable pavement. Leading the project is Ulla Visbech Madsen, a construction engineer at Køge Municipality. The pavement here is an IBF SF-Rima®, but the principle is the same—the site's base layer functions as a detention basin, holding the water so it does not strain the existing stormwater system during heavy rainfall. Rainwater from areas around the stadium is also directed to the parking area through water channels.

Service Agreement via NCC

Køge Municipality has chosen to manage the operation of the parking area on the campus itself, but it is also possible to establish a fixed service agreement with NCC, who will maintain and dispose of the collected material.

Demand for Rainwater Management Solutions

Køge Municipality has fully embraced the permeable paving solution and has addressed the significant challenges that Danish municipalities face with increasingly frequent and intense cloudbursts. At NCC, they notice that more municipalities are looking for solutions for managing rainwater.

"The future will bring more cloudbursts, which our sewers and roads cannot handle. Permeable base layers that drain rainwater away by themselves are increasingly being used as climate protection," says Michael Brask, Project Manager at NCC Industry, who has also been involved in the project at Køge Campus.

Secured for 100 Years

Back at the campus parking area, which to the naked eye looks like ordinary parking bays. The innovative paving solution truly demonstrates its value the next time a rain shower passes through. Even though we visit Køge Campus on a sunny day, one could almost wish for a downpour – just to see the technology in action. We'll have to settle for hearing Ulrik Lindberg recount the last major rainfall. The joints had been cleaned beforehand, and the large amount of rain was therefore no challenge for the vast parking area. With ongoing operation and maintenance, Køge Municipality will also not face challenges with the campus area's rainwater for the next 100 years.

Development of IBF Perma-Drain®

The IBF Perma-Drain® system is a collective term for IBF's permeable paving solutions. IBF has been working on the development of pavings for rainwater management for the past 10 years and has a selection of paving types suitable for this purpose. In addition to the 10,000 m² parking area at Køge Campus, IBF has also delivered the Perma-Drain® solution in several places in Horsens Municipality as well as to residential streets in Aalborg, Silkeborg, and Nykøbing Falster. The latest project is the paving around the old state prison in Copenhagen. IBF has also provided solutions for parking areas for private companies, which are also challenged by the increasing amount of water.