In New Zealand, as in many other countries around the world, population increases and escalating land prices have caused many local authorities to look at upgrading existing sportsfields to make them able to sustain a greater intensity of use, particularly during the winter months.
Challenges with
URBAN SPORTSFIELD DRAINAGE
M
ost approaches to sports field upgrading at local authority level in New Zealand involve the
spreading of a layer of sand under which is an arrangement of narrow spaced slit drains connecting into a standard lateral pipe drainage system (i.e.. the classic slit drainage/sand carpet system as is commonly used in the UK). Drain lines are usually installed using conventional trench excavation and perforated plastic pipes are usually the conduit to collect and transport surface water directed to them. Most systems in urban areas dispose of collected drainage water into the local public stormwater system. However, whilst city and district councils here have an obligation to improve public sports facilities and permit development, they are also required by law, under the Resource Management Act (1991), to enforce environmental protection and demonstrate that improvement works will not cause lasting adverse effects. Challenges arise when a site earmarked for drainage upgrading contains soil contamination, poor surface levels that would be difficult to improve without major earthworks, restrictions on the drainage outlet from the site, or no adequate outlet at all and the requirement to retain the site as a flood plain for ‘temporary storage of urban stormwater run-off under peak rainfall events’ (e.g. the one in ten year storm that now seems to occur every year). All are likely to result in some type of restriction being placed on the use of
conventional sports turf drainage approaches. In particular, when sports fields established on poor quality sites are improved, the Resource Consent process (the NZ equivalent of planning permission) becomes increasingly complex. As an example, Victoria Park in Central Auckland is a reclaimed area that was originally constructed in the early 1990s using infill material of varying quality.
Although reasonably flat, the site
suffered from poor levels from a sportsturf drainage perspective, with many water collecting hollows present. A conventional lateral and slit drainage system, installed in the early 1990s, offered an initial improvement in winter performance but, by 2006, was considered past its use-by date. Poor winter sports field performance was also exacerbated by the location of existing and disused cricket pitches within the sports field layout.
It was necessary to devise an upgrading process that minimised the risk to the environment but would still provide an improvement in surface conditions and give a good return on the upgrading budget available. However, it was quickly realised that there would be severe restrictions on the type of upgrading work able to be carried out for a number of reasons. These included the presence of protected trees around the perimeter and original infill material that was classified as contaminated. This meant that not only were major
earthworks over the wider site likely to be prohibited but also any spoil generated by trenching activities would have to be disposed of at a closed landfill. The site was also classified as a flood retention area. And, if the above wasn’t enough, the park was also listed as a Heritage Site, which meant that any development had to be sensitive to local cultural requirements. To put the above restrictions in perspective, the total budget available for the work would barely have covered the cost of spoil disposal in a closed landfill. The ramifications of the site specific issues affected almost every aspect of the proposed upgrading works. Restrictions on soil excavation and spoil disposal had the greatest impact on the installation of the new irrigation system and upgrade of a new drainage infrastructure.
Irrigation
The existing irrigation infrastructure was inadequate, suffering from low pressure, poor coverage and poor original installation. A limited budget and expensive spoil disposal prevented a new automatic pop-up system from being installed for each sports field; instead a new 90mm main line with hydrants for a travelling irrigator was installed using trenchless technology, along with 40mm diameter laterals to supply the new natural turf cricket blocks. Moling-in the irrigation infrastructure was completed during the summer. This was not an ideal time of year for moling operations and the extent of surface
If that wasn’t enough, the park was also listed as a Heritage Site
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