Recreational areas lead water away from the new Herlev Hospital

The Capital Region of Denmark is expanding Herlev Hospital and according to plan, the new Herlev Hospital will be ready for use in 2018. The expansion will add 60,000 new square metres and comprises, among other things, a new joint acute admissions department, a new women and children's centre, a new carpark, an extended service building and a new regional centre for sterile materials. Moreover new roads in the hospital area as well as a new exit from the premises will be added.

The expansion will create many new roofing areas and paved surfacing. These will increase the volumes of stormwater considerably, which need to be led away from the premises. "We know that the rainfall amounts will increase in future. We will experience more frequent rainfall, and sometimes also massive volumes during cloudbursts.

This will create more water, which we must be able to manage ourselves outside the sewer system. We need to do this because today the sewers are not dimensioned to deal with the large amounts of water. The sewer system is simply not able to keep up with the large volumes of water," said project engineer Jess Krarup from Herlev Hospital. Among other things, he has helped plan how the new Herlev Hospital is to manage the large volumes of stormwater in future.  He continued:

"Easements for the hospital's cadastre only allow us to discharge a certain amount of water. We're already exceeding this limit today. Our 'headache' is therefore how to manage more water within our own cadastre. This forces us to come up with alternative solutions."

The solution is to manage stormwater through infiltration. The basic idea is that the ambient landscape is to manage the stormwater, so the water is either absorbed through vegetation on roofs or on the ground, or it evaporates, infiltrates or is collected in water basins.

"The core in our solution is a higher degree of infiltration into the groundwater. In this way, we can lead some of the stormwater back into the groundwater layer. And we can lead some of the water through a low-lying area located in the outskirts of the cadastre. Depending on the weather, a small lake will be created here. At other times, this area will be dry," explained Jess Krarup.

Infiltration instead of discharge leads the stormwater back into a natural circulation. Furthermore, this reduces the load on the municipal sewer system and treatment plant. This also contributes significantly to the maintenance and balancing of groundwater reserves.

The actual infiltration of stormwater is primarily through green surface plants such as infiltration beds, trenches and verges. Secondly, infiltration is through permeable paving such as gravel, stony beds or asphalt that store the water in road beds/fascines under the actual wearing surface until it sieves down into the underlying soil, and finally into the groundwater.

Finally, there is overflow from the lowest water basins to an existing underground detention basin from where excess rainwater is gradually led into the municipal stormwater sewer.

With this solution, the cadastre around the new Herlev Hospital has been dimensioned to cope with five years of rain. However, due to the lack of opportunities to discharge stormwater to neighbouring cadastres, the courtyards in between the hospital buildings have been dimensioned to cope with 100 years of rain thereby reducing the risk of flooding indoor areas.

In addition to the benefits of surface water management, this solution also provides recreational benefits for patients in the Capital Region of Denmark. The landscape around the extended hospital will include green trenches, infiltration beds, vegetation, watercourses and water basins.

Add to this path systems and outdoor recreational areas. Overall, this will improve the quality of the hospital's open spaces to the benefit of patients, employees and relatives. Moreover, this ensures visible communication of a sustainable climate change adaptation measure.

Road water will also be managed through infiltration. Therefore the concept behind new Hospital Herlev's surface-water management focuses on road salt, which is one of the five greatest sinners in groundwater contamination.

Run-off of road salt into the groundwater has a negative impact on the taste of the water. Moreover, increased levels of salt in the groundwater may have negative impacts on human health (e.g. high blood pressure) as well as on the environment.

Therefore, as part of the surface-water management for the new Hospital Herlev suggestions have been made to replace de-icing agents from road salt to CMA (calcium magnesium acetate). Unlike road salt, CMA has a positive effect on plants and grass in the area as well as less run-off of other metals. In addition, CMA helps preserve the soil structure and benefits the infiltration capacity in the infiltration beds.