The times when space in a city was reserved for a single purpose only are over. Cities have to deal with challenges like intensified urban density and climate change, which require, in the case of new development or redevelopment, that every space be able to fulfil several purposes in order to preserve the city’s functionality, health and liveability. This also has implications for its sports grounds.
To meet the extensive playing needs, natural grass pitches are being replaced on a massive scale by pitches made of artificial grass. The big advantages of artificial grass are that it can be played on continuously, it requires no mowing, and its sprinkling needs can be met with a lot less drinking and surface water. But this development also has its downsides: for example, rainwater drains off artificial pitches very quickly and is discharged into surface water or the sewerage system, carrying with it discharged matter and microplastics. The result can be greater flooding and water-quality deterioration. This, while the large surface areas involved are ideally suited for capturing rainwater.
Moreover, the pitches become extremely hot under the blazing sun. So hot (>60 oC), in fact, that they cannot be played on comfortably, and can even cause health problems (McNitt et al., 2007). The conversion to artificial grass also means that the city is deprived of the cooling effect of evaporation from natural grass mats, thereby aggravating the Urban Heat Island effect.
Research in the US (Penn State, 2015) shows that evaporation is the only effective way of cooling artificial grass pitches. But this has its problems, namely: the effect of the required sprinkling is too short-lived, and it has a negative impact on the pitch’s playability, which, to be corrected, again demands (large) amounts of water. The sprinkling also brings with it health risks (especially when surface water is used), because the aerosols might be contaminated. Surface water sprinkling also leads to undesirable algal and bacterial growth in the artificial grass mats. A solution to both the warming of the pitches and the negative effects of the sprinkling and discharge is highly desirable.
In this project we are developing and testing a technical solution for the above-outlined problems with artificial grass pitches: the rapid discharge of (excessive) (contaminated) water, the considerable decrease in evaporation, and thereby the insufficient cooling and/or limited pitch playability. The core of the solution envisaged is the temporary storage of filtrated rainwater in a hollow foundation directly under the sports pitch (with water levels controlled on the basis of weather forecasts), and the capillary return of this water to the surface for evaporation. With this system the rainwater is retained (i.e., no discharge into the sewerage system or surface water), and remains available for evaporation and thus for cooling through the pitch itself.
The key challenge is the development and testing of a method for returning the water from the hollow foundation layer to the top of the artificial grass mat, where it can evaporate and cool the surface. This cannot for example be done at the expense of the pitch’s playability, nor can it lead to the growth of bacteria and algae in the mat.
The artificial grass system to be developed and tested in this project will make an important contribution to a sustainable and climate-robust urban living environment. This contribution will take shape by integrating the storage of excess rainwater – and thus the prevention of urban flooding – the evaporation of this water – and thus cooling and maintaining the better playability of artificial grass pitches – and the reduction of heat stress in the city. In view of the global character of the heat stress problem related to artificial grass pitches, we expect that the chances of a market uptake for the developed product will be good. Once developed, the system will be tested both in the lab and under field conditions. The field set-up will also make it possible to study the pitch playability and the integration of the system into the area’s water management.