Understanding Sports Pitch drainage
To properly identify the most effective, value-for-money solution to a particular drainage issue, it can be helpful to understand some of the underlying principles that govern water’s natural flow, how this can be impeded, and how this can be overcome.
Water – whether starting its journey as it falls in droplets from a cloud, flowing in mass as a mighty river, or puddling on a sports pitch – moves as a consequence of gravity. As such, rainwater that finds its way onto a pitch will follow the natural contours of the land until it is (hopefully) able to drain away. This is why Sport England recommendations specify a gradient of 1:100 along a pitch’s length, and 1:50 across its width: these gentle slopes encourage water to move across the playing surface, where a perfectly flat surface would only encourage water to puddle and pool.
Water does not, however, only move across the surface; it also moves into the surface.
Natural sports turf is porous, with tiny pockets of air between the various particles of soil, sand, and vegetation. These pockets of air are what the water moves through, and consequently they are crucial to land drainage – as we will discover in the ‘Solutions’ section below. Under ideal conditions, gravity’s pull will see a pitch’s surface water move through these tiny spaces in the ground and find their way below the surface. So far, so good – sub-surface water beats surface water hands down!
Problems with soggy, waterlogged ground can occur however, when this sub-surface water cannot move quickly enough – or indeed move at all – through the ground, and away from the pitch surface. This can be a consequence of one or a combination of a wide range of factors, from thick clay soil, to heavily compacted ground, to buried obstructions. Furthermore, the particular hydrology of any particular piece of land – say, a sports pitch – must always be considered in the context of its broader surroundings, with anything from water run-off from adjacent higher ground, to broken pipes or water mains saturating the ground with excess water contributing to the problems on any given piece of land.
As such, it is crucial to conduct a thorough, considered and holistic analysis of sites exhibiting signs of waterlogging, in order to properly identify the source(s) of the problem before investing in trying to solve the issue.
In almost all cases, the answer to poorly draining ground lies in the pockets of sub-surface air we discussed earlier, through which water travels (or – in the case of poorly draining ground – doesn’t!) Water’s movement through soil, sand or gravel is slow, with droplets seeping through the ground through one air pocket after the next.
When the natural composition of the ground provides insufficient sub-surface channels to quickly disperse the volume of water that falls – or otherwise finds its way – onto a pitch, that is when we must take matters into our own hands and give the water the help it needs to get away from our sports surfaces.
This is the principle behind all land drainage: from traditional French Drains, to conventional plastic pipe, to more advanced solutions such as Turfdry’s unique Hydraway Sportsdrain: by creating larger pockets of air in subsurface channels (the drains), water can move more quickly and effectively away from the area being drained, thereby reducing the saturation of the ground and mitigating waterlogging issues.
Secondary drainage techniques also work on this same principle, with sand/gravel bands encouraging water’s movement through the spaces between their coarse particles, away from the playing surface and into the primary drainage system. ‘Earthquaking’ machines operate on a similar principle, using powerful vibrations to create sub-surface cracks and fissures disrupting compacted ground and creating new channels for water to more easily move through.
Now we understand that drainage solutions involve the creation of sub-surface pockets of space through which water can quickly and efficiently move, we are better equipped to assess which solutions will be the most cost-effective use of resources in overcoming particular drainage issues.
A primary drainage system consists of a series of ‘lateral’ drains installed across the area in question, connecting to a ‘main’ carrier pipe that channels the water collected by the system to an outfall. So far, so simple.
The key determining factors in the effectiveness of primary drainage systems are: lateral specification, drainage design, and lateral spacing.
The conventional specification for lateral drains suggests perforated plastic pipes – usually 60mm or 80mm in diameter. It should however be noted that 60mm pipes are becoming increasingly unpopular, as 80mm pipes offer greater total capacity for the drainage system, and only involve minimally more disruption during the installation process.
Water enters the plastic pipe through its perforations, before being carried away to outfall via the main pipe. As a consequence of the size of these perforations however, plastic pipes can run the risk of blockage through the cumulative build-up of silt particles that enter the drain. Consequently, it is crucial that plastic pipe drains are installed at a minimum gradient of 1 in 200, which will ensure the velocity of the water’s movement through the pipe will be sufficient to ‘flush’ the system; in cases where these gradients cannot be achieved – perhaps as a result of a fixed height that a system is to outfall to – alternative solutions must be considered.
Turfdry’s unique alternative to conventional plastic pipe – Hydraway Sportsdrain – offers a number of advantages, and is increasingly being recognised as a highly cost-effective solution to sports pitch drainage problems. The key to these benefits is its highly engineered, clog-resistant lining, which allows water to enter the drain through tiny 140 micron diameter holes, whilst preventing silt infiltration. Consequently, the gradient demands placed on plastic pipe drainage systems can be overcome by Hydraway Sportsdrain, which has demonstrated effectiveness even at zero gradient.
An additional function of Hydraway’s unique construction is that – despite its width of only 25mm – it has a greater surface area than plastic pipe drains; moreover, a higher proportion of this surface area allows water intake to the drain.
In view of the established principle that effective drainage is the provision of quick and efficient means of water’s movement, it is easy to see how Hydraway’s rapid water intake results in dramatically faster drainage performance: the more easily water can make its way from the ground and into the drain, the faster the ground will dry. In addition to its success on sports surfaces, this quick drainage performance has also seen the Hydraway system used as part of flood mitigation schemes due to its fast response to sudden downpours. Moreover, the narrow width of the drain in comparison to a plastic pipe lateral means that future sinkage of the drains as the ground contracts in hot weather is minimised.
For more information on the specific benefits of the Turfdry Drainage System using Hydraway Sportsdrain, please visit our website: www.turfdry.com
In designing a drainage system for a sports pitch, the natural falls of the land must be accounted for in determining the optimal angle for the lateral drains, where the necessity for positive flow through the drains must be balanced with their intersecting surface water most effectively.
If in doubt, it is always better to consult a contractor with design experience before settling on any particular specification or layout for a new drainage system, as these decisions can have a long-lasting impact on the effectiveness, and value-for-money delivered by a primary drainage system.
As a result of the wide range of variable factors involved (soil types, pitch gradients, frequency and type of use, rainfall statistics for the location, maintenance regimes, etc.) there is no practical scientific formula to determine the ideal drain spacing for any particular sports pitch. However, Hooghoudt’s Drain Spacing Equation shows that any percentage increase (x) in the amount of drains will increase the overall drainage rate achieved by double that percentage (2x).
For example: changing from a 3m scheme to a 2.5m scheme involves a 20% increase in the amount of drainage installed, but will result in a 40% increase in the overall drainage rate achieved.
Consequently, it is sensible to install lateral drains with as tight a spacing as budgets will allow for, with each step closer together the drains are installed at significantly increasing the cost-effectiveness of the project.
In cases where functional, but inadequately spaced primary drainage systems exist, secondary drainage solutions such as sand-slitting (typically 300mm x 50mm excavated trenches filled with sand-over-gravel) or sand-banding (non-excavated slits at fixed 260mm centres, injected with sand) may prove effective in encouraging surface water that moves across the pitch to find its way more efficiently into the primary drains, thereby increasing the rate of drainage. This can lend a new lease of life to an ageing draining system, increasing the rate at which surface water can find its way into the primary drainage system, thereby improving its performance at relatively low cost.
For this to be an effective solution however, it is imperative that one is confident the existing primary drainage system is and will remain operational, offering a good flow rate through unobstructed pipes to a positive outfall (such as brook, pond, or sewer).
In cases where existing drains are blocked, water collected by the system will work its way to the point of the blockage, where pressure will build as more water backs up into the system; with no positive outfall to drain to, the rising pressure in the pipe will eventually force the water back out of the drainage system, causing further waterlogging issues. In cases such as these, secondary drainage solutions – no matter how effective – will not overcome the underlying issues that are the root cause of the waterlogging.
Secondary drainage solutions can be an excellent way of delivering relatively quick, affordable, and minimally disruptive improvements to a pitch’s drainage. However, it should be noted that – as a consequence of their less ‘invasive’ nature – secondary drainage solutions have a significantly shorter lifespan than primary drainage solutions: pipes will weather the test of time substantially better than gravel channels or sub-surface fissures, and so this should be considered in contemplating the long-term cost-effectiveness of drainage proposals.
Turfdry does not stand alone in the industry when it comes to embracing new technology to develop new solutions to sports turf drainage problems: it is unlikely that Hydraway Sportsdrain will be the only ‘miraculous’ solution you will ever hear about from a drainage contractor. Furthermore, experts may differ on what particular solution or combination of solutions is most appropriate or cost-effective for any particular issue. Nevertheless, Hydraway does have an impeccable, 25-year track record in UK sports turf, and has been independently tested and proven to be successful. Few, if any, other ‘miraculous’ solutions can claim this to be true.
It is our hope, that this article has offered some insight into the underlying principles that determine the suitability or effectiveness of any drainage system, equipping you to make more objective, informed analyses of future drainage projects or solutions you may consider. After all – whilst we may be the experts on sports turf drainage, you are the expert when it comes to any project you might seek to undertake: its budget, its goals, the expectations you have for it, and the particular features or needs of your site. As such, we hope that sharing some of our expertise helps empower you to make the best decisions for your site, and its end-users.