Green on brown

An approach to developing high-quality sports pitches on brownfield sites – achieving a legacy to be proud of

By Alex Vickers, consultant for Turf Trax Ground Management Systems

Brownfield sites are commonly developed into sports pitches as part of wider regeneration programmes. This can present real challenges if sustainable, high-quality sports surfaces are to be established. The most obvious challenge is dealing with any contaminated land issues present at the site. This is particularly pertinent for cut and fill, grading and drainage works that could potentially expose contaminants to sensitive receptors.

Optimising surface performance with minimal use of imported materials

In such situations, expertise in contaminated land remediation should be sought. In doing this, however, it is vital not to lose sight of the required end use and the characteristics needed to ensure the sports pitches produced are fit for purpose and also sustainable for those who manage them. Frequently, a traditional civil engineering approach results in pitches that have certain engineering characteristics such as stability, surface evenness and a backbone of land drains but as an environment to support a living sward of grass and to provide the required playability for the sports in question, they can leave a lot to be desired.

One approach to dealing with sites that have some contamination issues is the careful mapping of the areas affected. This facilitates sensible planning of the site layout so that the natural turf pitches can be located in the least sensitive areas. There is often more scope to place synthetic playing surfaces, or other areas of hard standing (such as car parks), over the contaminated areas where the quality of the soil material is less important.

Figure 1 shows the results of an Electro-Magnetic Inductance (EMI) survey of existing amenity land built over an old sewage works, where the reconstruction of four natural turf winter sports pitches and a training grid was planned. The scan clearly identified the extent of the old works (darker coloured area) and, when validated by targeted soil sampling and analysis, allowed different approaches to be taken to reconstructing and improving the sports fields on the site.

EMI soil variability maps showing the extent of made
ground at a site in Hampshire, UKd

The EMI survey allowed engineers at TurfTrax Ground Management Systems to avoid designing any pitch construction works that would have penetrated the soil cap above the contaminants. The approach in this case was to import clean topsoil to build up levels in the main rugby pitch (sited over the contaminated area), thereby allowing the pitch to be graded level and then drained without cutting into the contaminated layers below. The quality of the topsoil was vital to success in this case, as spending marginally more at this stage ultimately saved considerable sums of money later on by negating the need for supplementary drainage installation.

To use this approach on all four pitches on the site would have been cost prohibitive, however the scan allowed the extent of contamination to be mapped and the remaining pitches were relocated off the contaminated area on the existing clean, natural soil. This allowed all four pitches to be improved for less than one third the cost of reconstructing them all on the same basis as the rugby pitch.

When pitches are constructed on brownfield sites they are often built directly in the engineering cap (many sites do not have an agricultural or restoration cap to speak of), producing very low-quality pitches that drain and perform poorly. Alternatively, they are built on very thin layers of free-draining material above the compacted engineering cap. In such situations it is possible that very little play (especially in respect to winter sports) takes place even up to three years post-construction. Avoiding this is relatively simple – and hinges on the careful selection of the capping material. Obtaining the cheapest top-soil or soil-forming material may make economic sense at the time, but the cost of reconstructing failed sports pitches years later can be very significant. Clearly, an engineered cap must meet its primary purpose of isolating the material below the cap. Therefore, rather than risk the integrity of that material, it is better to add sufficient topsoil material to allow a drainage system to be installed safely. A minimum depth of 500 mm for a lateral drainage system is required.

By carefully designing a drainage system, it might be possible to use lower quality soil material for most of the build-up and then have a thinner layer of better quality material that will drain effectively as a result of the supplementary drainage. An example of this is shown in Figure 2.

In this case, a shallow depth of free-draining sports rootzone material is placed over a network of shallow, close-centred slits filled with the same rootzone material. This creates a much deeper effective drainage depth due to the hydraulic connection between the material in the slits and the material in the surface layer.

A key drawback to the use of very free-draining materials is the effect this has on water and nutrient requirements. Typical specifications for top-level pitches have drainage requirements in the region of 150mm per hour. The inevitable consequence of this is the use of sand for construction and the need for intensive irrigation and fertilisation to maintain turf vigour and surface stability.

At a time when efficient water use is required, this approach cannot be sustainable in any situation outside of high-level professional sport. To this end, the use of suitable natural soil and the creation of deep profiles over engineering caps may be a more effective solution in the longer term. Carefully managed, such soils can create excellent pitches.

In conclusion, careful planning can result in significant savings in construction costs and in the long-term sustainable performance of sports pitches constructed on brownfield sites. Sadly, pitches are often built with little thought regarding their long-term use, sustainability or minimum performance requirements due to all the emphasis being placed on isolating the contamination. This either leads to expensive remediation work and pitches that are still compromised by their initial construction, or worse, to pitches that are of no use to their community at all. When done well however, the reputation of the developer is enhanced and the sporting legacy remains of value for many years.