Copenhagen Zoo retains water

The infiltration system has been put into service. New and similar projects are in the making

The infiltration bed at the Zoo was put into service in 2015. It has already proven valuable during heavy downpours and it is the first phase of a number of projects to retain water at the Zoo.

The Zoo is ISO14001-certified and part of its environmental vision is to save on resources wherever possible. When, in 2015, the Zoo set out to establish a new enclosure for Tasmanian animals, retaining some of the rainwater and using it for cleaning was a matter of course.

The Zoo is situated at the highest point in Frederiksberg. The Zoo's area is therefore important in terms of retaining rainwater and protecting the city's residents against cloudbursts. The local utility company, Frederiksberg Forsyning, and the Zoo therefore established the infiltration bed with its 650 infiltration cells.

The installation was ready for operation in 2015 and was funded by the local utility company, Frederiksberg Forsyning. The installation is designed to cope with a 100-year event and has an expected lifetime of 25 years.

The installation is the first part of a larger plan to decouple rainwater from the sewer system.

Densely built-up urban area at risk during cloudbursts

Repeated cloudbursts have caused repeated flooding in many places in Frederiksberg. It therefore seems obvious to use the Zoo, which is located on higher ground, to hold back some of the water.

Frederiksberg Municipality is Denmark's most densely populated urban area and also has a very high percentage of paved area. Therefore the city's residents are very vulnerable to flooding during cloudbursts. The Zoo lies at the highest point in the municipality.

The local utility company therefore seized the opportunity to install an infiltration bed when it was contacted in 2015 by the Zoo about a project to retain rainwater at the Zoo.

The infiltration bed can hold up to 142 cubic metres of water

The 650 infiltration cells have been installed in two layers and are connected to several rainwater reservoirs.

In 2015, the Zoo established an overall area plan, including water catchment areas. Every time there are development or renovation works at the Zoo, the work will take account of the overall hydrology of the area.  This means the Zoo can best exploit the rainwater resources.

The 650 subsurface infiltration cells in the Zoo's Tasmanian enclosures are traditional, mutually connected plastic chambers from which the water can slowly permeate down into the subsurface. Three collection reservoirs direct the rainwater onward to the infiltration cells.

The Zoo uses part of the rainwater collected from the collection sites to rinse pools and animal enclosures, as well as for other cleaning purposes in the Tasmanian facility. A water treatment system has therefore been coupled to the collection reservoirs.

Generally, the Zoo is working to incorporate local rainwater drainage solutions in several places, but the infiltration bed at the Tasmanian facility is the first actual climate-change adaptation project. In addition to the infiltration bed, several of animal sheds have green roofs and a new lake on the savannah has been coupled to a rainwater collection installation. The infiltration bed has an expected lifetime of 25 years.

Bona-fide win-win solutions for the Zoo and the residents of Frederiksberg

The Zoo saves money and creates value from rainfall. And Frederiksberg residents have better protection against flooding. In the long term, Zoo visitors will have more experiences with water.

Rikke Bydam, environmental coordinator at the Zoo, and Henrik Bay, head of department (Water) at Frederiksberg Forsyning, agree that the water projects at the Zoo are bona-fide win-win solutions.

The Zoo has a very large water consumption for its large animal population. By collecting rainfall and using it to clean and rinse enclosures, the Zoo can save valuable water resources. In Rikke Bydam's words it makes absolutely no sense to use high-quality drinking water to rinse pools and animal enclosures.

The Zoo has not presented a statement of how much water the rainwater collection facility saves. And Frederiksberg Forsyning has no accurate information on how much water is kept away from the urban residential area below the hill. However, the infiltration cells at the Zoo are part of the plan to protect the entire city of Frederiksberg against 100-year events and to ensure the city never has more than 10 centimetres of stormwater above ground. The infiltration cells at the Zoo are a small piece of the puzzle to ensure this.

Financed by the utility company

The infiltration system has been paid for by Frederiksberg Forsyning, the local utility company.

In addition to the infiltration system, Frederiksberg Forsyning has also paid for the subsequent project to retain rainwater at the Zoo.

Maintenance of the infiltration bed is also being paid for by the utility company. The other installations around the water-technology installations are being paid for by the Zoo. The Zoo also pays for stormwater processing and treatment.

Smooth collaboration between two parties

The idea for the project came from Copenhagen Zoo, which sent a proposal to Frederiksberg Forsyning. The utility company seized on the opportunity to manage more rainwater.

The two parties were in agreement about the project from the very beginning.

Today, the Zoo and Frederiksberg Forsyning still meet regularly to follow up on existing and new joint rainwater projects.

At the same time, Frederiksberg Municipality and Frederiksberg Forsyning have a joint cloudburst secretariat that manages solutions in the entire municipality.

The infiltration system solution at the Zoo required approval from Frederiksberg Municipality. Furthermore, the health inspector granted authorisation to use rainwater at the Zoo, as visitors can come into contact with the water.

Only water quality posed minor challenges

The infiltration project at the Zoo ran smoothly from idea, over planning to execution and operation.

The only slight challenge has been linked to the rainwater that the Zoo wanted to use for cleaning and rinsing animal enclosures.

This was due to an elevated content of plasticisers in the runoff rainwater from the rubber roofing on areas of the Zoo's tropical house.

However, authorisation was granted following an assessment that the water from this rooftop is diluted by the runoff from other surrounding roof surfaces and by adding tap water.