Drainage for sports fields or ponds and wetlands

Amenity & Sports Drainage

Croft Drainage Solutions use Shelton Sportsturf and Agricultural Drainage machinery and techniques to deliver sustainable solutions.

These drainage techniques allow speedy new drainage installation with little disruption to the surface but the timing of the drainage works needs to be selected with care for optimum results – some drainage techniques are best undertaken when soils are relatively dry, others when soil moisture levels are relatively high. This means it helps to plan ahead to minimise disruption.

The first step in the process is to try and identify the reasons for the excessively wet area. Perhaps it is naturally slow draining clay soil, maybe substantial rainfall over a short period, possibly soil water rising from below, or run-off from adjoining higher ground. It may be caused by excessive thatch or capping of usually well draining soil by heavy pedestrian or mechanical traffic. Is it a broken land drainage or a damaged irrigation pipe? Until the reasons for the problem are identified the best and most cost-effective solution cannot be formulated.

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The use of spherical materials are the preferred choice to help with drainage as they leave air spaces for water to flow through.

Angular gravels tend to run together over time leaving no such spaces. Materials with lots of fines should also be avoided to prevent pipes from becoming blocked.

Crushed 8-10mm gravel may be inexpensive but a product such as Lytag – pulverised fuel ash – could drain up to ten times faster. The advantages of using Lytag are many, including faster drainage, the ability to retain water in dry conditions which reduces the striping that can occur when gravel is used.

It is half the weight of gravel per volume, which reduces the weight of material being carted across the site. It also shatters on contact with mowers, where gravel will not. The latter could be the more cost-effective material to use; it will depend on your circumstances.

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Primary Drainage

To remove excess soil water from an area is going to require the use of perforated land drainage pipes. It is important not to over-size these pipes.

The reason for this is that very small soil particles pass through the slots in the drainage pipes and are flushed out by the flow of water. The bigger the pipes the slower the flow of water: if the flow is too slow then the fine particles build up in the pipe and quickly reduce its effectiveness.

Correct pipe sizing is very important; the designer of the system will take a number of variables into account in deciding the appropriate sizes for a particular installation. Substantial sums of money can be saved by getting things right at this stage.

To minimise disruption the layout of the lateral piped system must connect with a main drain or drains off the playing area. The herringbone system is ‘out’ for the pipe junctions are sited down the centre of the pitch resulting in big scars in the most-used part of the pitch.

Spacing of the lateral drains will be determined, most likely, by the budget. On a top quality surface 3-5 metre spacing is likely. Whereas 7 or 10 metre spacing is more common where budgets are tight. 10 metre spacing should be considered the maximum.

But pipe sizes and consequently trench width are also major cost considerations. The larger the pipe, the wider the trench, and hence larger quantities of aggregate are required to backfill the trenches. Narrower trenches also heal quicker. Main drains would typically be 100mm in a 118mm trench, trench laterals being 60mm in a 78mm trench or 80mm in a 97mm trench.

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Secondary Drainage Techniques

Piped land drains remove excess soil water off the pitch or amenity surface and whilst it might be desirable to put these close together the cost, in most cases, would be prohibitive.

Therefore, it is usual to space them at 3, 5, 7 or 10 metres apart depending on the status of the pitch. (Some of the excess water in the soil therefore has to travel between 1½ to 5 metres to the nearest land drain and this takes time.)

To speed up this water movement through the soil a secondary drainage system is superimposed over the primary system, usually at 90° to it.

The systems we use are:

One of the commonest systems has been sand slitting or slit trench drainage. This consists of 50mm wide gravel/sand filled trenches installed using a Supertrencher, spaced one to two metres apart. They are typically 250mm deep, backfilled with 100mm of gravel, and topped off with 150mm of coarse sand. These are best installed in dry conditions.

Gravel Banding

Shelton Gravel Band Drainage consists of gravel bands, usually 25mm wide and 250mm deep. The soil is opened up by a vibrating stainless steel tine and the gravel fed immediately into the slot. A wheel or roller on the back of the machine partly closes the band to enable use of the surface immediately afterwards. This system has to be installed when the soil is moist throughout the working depth. This gravel banding is low cost, yet very effective. Because the bands are close together and half the width of the slit trench drainage technique only rarely do they open up to such an extent that remedial work is required. In such cases an overall surface dressing of a free draining sand suffices.

Gravel banding has become a popular technique on all surfaces form professional pitches to pitches and amenity areas in small towns and villages.

System 25

System 25™ is a trenching technique where 25mm wide trenches are dug by a high speed wheel. The arisings are conveyed into a trailer running alongside. Coupled to the rear of which is a vibrating hopper immediately back-filling the trench with a permeable aggregate. It is a one-pass operation.

These micro trenches are usually installed at depth of 300mm and are usually spaced between ½m and 2m apart depending on the speed of drainage required, and the budget available. Shelton System 25™ is best installed when the soil is on the dry side. It entails the use of more equipment and operators than gravel banding hence the cost is somewhat higher. Disruption to the playing surface is minimal and use may be resumed immediately if necessary.

Lightening Drain

There are situations where very speedy drainage is required. To meet this demand Shelton have recently introduced our Lightening Drain™ system; the world’s fastest drainage system.

Lightening Drain™ is very similar to System 25™ , using the same equipment, except the trenches are dug 35mm wide and a 25mm perforated land drainage pipe is installed prior to backfilling with Lytag. We know of no faster land drainage system when the pipes are spaced at 500mm centres.

Drainage maintenance

With all secondary drainage systems maintenance is required. A common failing arises because the surface drains well.

As a result they are heavily used for matches, training and general recreation. The grass turns to mud and the effectiveness of the secondary system is thereby reduced.

After the installation of secondary drainage and in years two and three it is advisable to apply 100tonnes of a free draining sand to the surface in the growing season – preferably in two applications of 50 tonnes so as not to suppress grass growth.

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