Keeping Sports Pitches Firm and Free of Surface Water

The Groundsman, April 2000

With summer fastly approaching memories of muddy and persistently wet playing surfaces over the winter months soon fade – and yet the forthcoming dry months offer the best opportunities for successful drainage installation.

In most instances these greasy quagmire-like pitches have developed simply because rain water has been unable to move downwards into the soil. Surface grading on many pitches is far from acceptable and gradients are generally not steeper than two percent. With little scope for run-off surplus water collects moving to slightly lower areas to form puddles and with the compaction and pugging that follows an almost unpenetrable surface develops. Where it exists, accumulating grass thatch too collects and hold surplus water and, to top it all, if earthworms are active even a well grassed pitch soon becomes a mud bath.

Where the budget permits – as on premier sportspitches – installed improved rootzone mixtures enable ready infiltration with surplus water being led away by an underground drainage. Even then, as we have seen on television, there remain disasters. Playing football or rugby in continually wet conditions soon compacts marginally improved rootzones and there is a natural separation of the fine silt fraction on exposed soil areas.

Surface wet areas can easily be confused with the presence of underground water. This is a different problem entirely with excess water accumulating from seepage through lower layers – often where there is high ground above the pitch – or merely from the existence of a high water table. However, on most high lying sportspitches with clay deep into the profile or chalk not far below, high water tables seldom occur. In the lower lying locations the presence – or absence – of underground water must be established. Where evident, a properly designed pipe drainage system, installed to a minimum depth of 600-700mm below the grassed surface, is essential to restrict the influence of water surplus in the rootzone depth.

Solutions to surface water

It should go without saying that the first measure must be to prevent water run-off from higher ground on to sportspitches. In some instances regrading – completely or partially – should be considered and earthworm activity must be controlled at all times.

Assuming the importing of approved sandy rootzone mixtures is beyond the budget of most clubs, the only viable solution is a well maintained surface water by-pass installation which involves the installation of closely spaced (one or two metre spacing) slit drains generally 50mm wide, together with lateral drains to a collector mainline that discharges at a suitable outfall location.

Gravel banding, a new innovation in which slits are opened in the soil without material being removed, can be installed at a closer spacing of 400mm to complement slit drain or even lateral drainage systems. Grooving can further supplement slit drain installation with 13mm wide slits, 200mm apart, 100mm deep. Recent equipment prototypes offer further possibilities in creating close spaced sand filled slits to promote quick removal of surplus water.

The overall success of any by-pass installation is however directly dependant on the degree of aftercare and annual maintenance. In fact, the maintenance effort entirely determines the success or failure of the installation. The main objective must be to promote a dense and vigorous grass cover, regularly topping up slits on drains, but more essentially, to apply regular sand topdressings – at least annually – to a depth of 6 to 10mm. The quicker a 25mm sand layer is crated over slits and drains the better – for it is only by so doing the surface openings are kept clear of sediment and organic matter that restrict infiltration and removal of surface water.

These by-pass installations are not without disadvantages however. During hot dry months, if no irrigation is possible, heavy loam soils readily contract opening up slits and trenches with the consequent loss of aggregate to lower layers. Immediate topping up slits and drains are essential to establish a level grade, but it is vital to sustain a good grass cover over these slits by ensuring regular fertilisation. Healthy grass cover reduces the possibility of slits and trenches opening up, but in extremely dry periods irrigation is the only means of preventing the cracks from appearing.

While the maintenance demand, with increased fertilisation, irrigation, topping up slits and drains and regular sand dressings, becomes a costly annual drain of club funds, the long-term cost together with installation remains a very small proportion of the cost of importing a suitable rootzone material – which too requires far more maintenance than is needed on unimproved heavy soil pitches.

In essence it all depends on the standard that must be maintained. With increased play during the wet winter months, this installation stands alone between a firm playable surface and a quagmire.

Gordon Jaaback

April 2000

 

Would you like more information? Please contact me