0 Post Drainage Blues

AFT.jpgThe recent wet winters have produced problems on many winter sports pitches. Often the first line of approach is to install an intensive pipe drainage scheme. Clubs commonly expect such a system to work immediately, to require limited maintenance and, worse still, are frequently forgotten about.

Problems often encountered following drainage installation lead to …Post Drainage Blues

This article assesses the common problems often associated with new installations and attempts to provide some solutions. However, it is vitally important to gain advice from your consultant, as specific situations will require specific solutions.

The problems!

Typical issues and problems that occur are:

• Drain line subsidence
• Difficulty to grow grass in the summer, especially over drain lines
• Poor drainage and compact surfaces

Each of these will be examined below and causes and solutions presented.

Drain line subsidence

Groundbreaker.jpgA frequent reason for subsidence is that clay soils can shrink in long spells of dry, late spring/summer weather. As this happens the drain trenches often get slightly wider and the backfill over the pipe settles, often creating a depression over the drain. Subsidence can be as much as 100-150mm but, more typically, is 25-50mm (see image 1).

Sometimes, however, the material in the drain trenches settles as the trench widens due to soil shrinkage, but the turf on the immediate surface does not settle, thus leaving a void underneath. This can be a particularly worrying condition, as the first you may know about it is when someone's foot goes through the surface into the underlying void, often sustaining an injury in the process.

It must be pointed out that these are natural problems but, occasionally, there may be problems due to installation techniques or the use of inappropriate materials. Certainly, great care is needed to avoid settlement as a consequence of these inadequacies.

The first solution to settlement/subsidence is to top up the drain lines with a similar topdressing to the top 150mm of the drain. This should be targeted during the early summer (maybe on a few occasions) to allow regrowth of the grass over the drains.

The application of irrigation during the summer to prevent or control the clay moisture content, and thus minimise settlement, is also an effective way forward. This should also help favour the development of good swards. However, in dry regions of the country, this could have a high cost, both financially and environmentally, and may not be acceptable.

The use of rotary decompactors, such as those from Blec, Earthquake, Imants etc., may provide an alternative solution. The principle of these machines is to cut a slit and decompact the soils around the drain. This introduces many fissures in the soil and, as the clay shrinks, reduces the pressure on the drain lines. It also has the benefit of effective summer decompaction. It would probably be best to run the machine parallel with the drain lines as far as possible and to undertake the work when the soils are dry or drying out. This could well help to reduce the severe drain line settlement.

Grass health problems

Photograph 1.jpgPhotograph 2.jpg

Image 1 Image 2

Drainage is designed to remove excess water from a pitch, although this may cause a pitch to become droughty in the summer. In addition, a pitch may tend to receive a greater number of matches due to better performance in the winter and, hence, become more compact hindering sward regrowth.

A solution is to ensure renovations are undertaken in a timely manner following the end of the season and whilst the soils are still moist. Seed could be drilled into the surface to prevent excessive desiccation. Thereafter, irrigation may be required during the first four weeks of establishment and, subsequently, if the sward becomes droughted. New constructions also often need higher levels of nutrition in the early months to ensure ongoing good growth

Goalmouths and centre circles are often difficult to re-establish due to drained but very compact soils. The use of turf and/or surface cultivation often fail as there remains a firm base immediately below the treated area. The best way forward is to deep cultivate or thoroughly break up any compaction pans, possibly incorporating some medium-fine sand and seed. The aim is not to create an excessively sandy profile that may destabilise, but to give a good tilth, especially in clay soils. This may take longer to establish but will improve the chances of keeping the grass cover during long spells of very wet winter weather.Maestenbroek.jpg

In many cases, the drain lines are difficult to grass over due to their very sandy nature. The topping up of a drain line with a more soil-rich medium may help, as would including Cation Exchange Capicity amending products. This could well have the slight effect of reducing the surface percolation rate and, therefore, appropriate soil assessment is essential. Eventually, the action of worms often mixes the soil and allows a sward to establish.

Poor drainage

Sometimes, following drainage installation, the pitch remains wet and poorly draining. This may be due to the use of poor materials or the specification being inadequate. However, there can be other causes, typically excessive compaction, over-use and expecting the pitch to work above its drainage design rate.

Compaction is very common on new sites and, in heavier soils, will prevent water from entering the topsoil or reaching the drain. Drains work by removing water from the surface, but also from the soil volume. If there is compaction then these routes are blocked and drainage can fail. Therefore, regular decompaction operations, up to four times per annum, and monthly solid tining will greatly assist in water penetration.

Any natural turf surface will have a limit in wet winter weather conditions as to the amount of wear it is able to tolerate. This will often be quite low and even the best specification is sometimes unable to cope with over eight hours use per week. Over-playing of heavier soils, particularly when moist, will de-structure the top level of the soil profile and limit water percolation. To reduce this, care needs to be taken and play reduced should liquefaction occur. It is also possible to apply a very light dressing of medium-fine sand onto any areas showing any wetness as this will, over time, improve the surface soil texture (see image 2).

It must be noted that all drainage systems will have a design capacity. Typically, a close centred system on a clay soil could be around 100mm per day. This may sound high but this relates to around 4mm per hour. Therefore, should a significant rainfall event occur immediately prior to a game, the pitch would not have had enough time to drain. This would lead to damage and soil de-structuring.

One solution may be to move the pitches as soon as wear is noted. Normally, wear occurs through the centre line so, in some instances, the pitch could perhaps be moved one goal width to the left or right to reduce the wear line. Alternatively, a different pitch location could reduce playing the same area.

Conclusions

This article hopefully shows that many problems which occur following drainage and construction works are often caused by natural processes or lack of maintenance. In all cases the costs of the first five years of maintenance need to be budgeted for. This gives a true reflection of the actual cost of the project. It is sometimes essential to use an agronomist to give precise recommendations during that time.

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