CitySports – climate-adaptive artificial pitches

Problem outline and project idea

Artificial pitches are an increasingly common sight in urban settings. They have the edge over natural grass pitches in a number of respects: artificial pitches can be used intensively, they require little or no sprinkling, and mowing is unnecessary. But there are also drawbacks. Rainwater containing leached substances and microplastics flows away quickly into surface water or the drainage system. That can exacerbate problems with excess water and make water quality worse. Furthermore, artificial pitches without shelter from the sun are, because of high temperatures (>50°C), unpleasant to play on and they strengthen the Urban Heat Island effect. Cooling by irrigation (evaporation) works for only a short time, it requires large amounts of water and, particularly when surface water is used, it involves health risks due to possible contaminated aerosols. In addition, sprinkling with surface water leads to the undesirable growth of algae and bacteria in the artificial turf. A solution is needed for both the warming up of the pitch and the negative effects of run-off and the lack of storage capacity.

Challenge

A technical solution has been tested that allows infiltrating rainwater to be stored temporarily in a hollow foundation immediately below the surface. Capillary action returns this water to the surface, where it evaporates and cools down the pitch.

The main challenge is to develop and test a method to return water from the hollow foundation layer to the top of the artificial pitch. This must not, for example, impair playability or result in the rampant growth of bacteria and algae.

Implementation

The system has been tested at different scales. In the first step, a lab experiment was conducted to determine the best combination of the type of artificial pitch, the shock pad and the infill for evaporation purposes. Test sections measuring 5mx5m were then laid out at the Marineterrein location in Amsterdam with different types of pitch. In addition, a training pitch with capillary irrigation was installed at the VVA/Spartaan (Laan van Spartaan) football club.

Multiple sensors were installed at both the test sections and the training pitch. They were used to measure, among other things, differences in surface temperature and meteorological conditions. The properties of the training pitch as a playing surface were also inspected immediately after the pitch was put down and after one year of play. In addition, a water management system was installed here with the aim of identifying the optimal balance between retention, drainage and the possible replenishment of water for adequate evaporation.

Results

The experiments demonstrated that it is possible to evaporate water through an artificial pitch with the system that has been developed. In the laboratory, evaporation was 3 mm/d; in the test sections, an evaporation flux of 4 mm/d was measured. At the Marineterrein location, the surface temperature of the conventional artificial turf was more than 50°C on several days; the temperature of the cooled artificial pitches was similar to natural grass in those cases. The air temperature above the conventional artificial turf at the Marineterrein was also higher than above the cooled fields. This rise in temperature lingers for a long time, particularly at night.

The temperature difference was lower at the Laan van Spartaan location. The cork infill in the existing artificial pitch there meant that it warmed up more slowly than at the Marineterrein, where a black rubber infill was used. On hot days with a lot of radiation, the cooled pitch at VVA/Spartaan was 5 to 10°C cooler than the conventional pitch.

In the test sections at the Marineterrein, it was possible to store rainwater effectively in the system and make it available for evaporation. In the summer of 2020, water storage in the cooled pitch was 83.8% and evaporation was at 69.9%. This is many times higher than the 13.8% of total precipitation that was retained and evaporated in the conventional pitch. Because of problems with sensors and possible leaks, it was not possible to determine how effective the system was at the Laan van Spartaan location.

With the 85mm-high Permavoid foundation layer under the artificial pitch, it may be possible to comply with the municipal requirements for water storage (60mm before 2022, 70mm after 25 March 2022). Unfortunately, it was not yet possible to achieve this during the trial period since this would have required the active (i.e. weather-dependent) control of the system, with trade-offs between the cooling and water storage. Furthermore, the bottom connection in the water buffer requires a technical modification so that the buffer can be emptied far enough.

The cooled field at the Laan van Spartaan location met the requirements for safe sporting use during both inspections. After a year of play, the only shortcomings were that the vertical ball bounce was slightly too low and the roughness was too high for the general requirements relating to artificial pitches. The values found are more in line with a slightly damp natural pitch.

At the Marineterrein, there has been plant growth in the cooled test sections and algae/bacteria growth is also apparent. It is important to note here that these pitches were not walked on during the monitoring period and a lot of dust blew in from the surrounding unpaved area. The Sport en Bos department (of the City of Amsterdam) has said that plant growth in artificial pitches with a sand infill (such as the systems tested) is normal if the pitches are not played on. At the Laan van Spartaan location, limited plant growth is apparent only in the edges near the fences. There has been no plant growth in the areas played on. Microorganism growth in the infills of the pitches with capillary irrigation is significantly lower than in the SBR rubber infill in the conventional turf pitch. The growth potential measured shows that biofilm development is a possibility in the water storage layer of the system. Despite the risk of the growth of opportunistic pathogens, the probability of athletes being exposed to them is very low. If the water is used for other purposes (sprinkling/water during play), this factor, and the faecal load – for example from birds – mean that disinfection is recommended.