Market report - Turf reinforcement

Ground solutions can help to overcome flood risks caused by impervious materials, says Maureen Keepin.

PERFO-AK Anchor tiles - image:  PERFO UK
PERFO-AK Anchor tiles - image: PERFO UK

Keeping ground areas porous but durable is a key reason for using turf reinforcement products. Acting as a free-draining field, reinforcement options include a polyethylene mesh, which is generally rolled out over cut grass and then pinned to the surface.

Cell structures are also available. These include ones that are laid on a prepared surface, secured and then infilled with aggregates or soils and seeded. A gestation period for seeds to germinate and grass to establish is often necessary before use, although some of the systems now available can be used immediately.

This type of material is classed as a sustainable urban drainage system - the porous surface affects the efficient attenuation, infiltration and treatment of storm water run-off. This scores high environmental points because it is now recognised that hardstanding speeds up the flow of water into rivers and can contribute to local flooding.

It is important to point out that some systems will not solve the problem of extremely boggy areas and excessive water on site where remedial drainage work may be required before their application.

Increasingly, these systems are also being used to protect steep slopes and river banks from wearing away. Although natural vegetation provides a level of soil erosion protection, this can be insufficient in certain locations such as coastal sites.

Turf reinforcement usage includes car parks, access roads, pedestrian areas, grass verges, cycleways and picnic areas. These systems can be installed as either a temporary or permanent solution to protect and strengthen the ground and grass.

New PERFO-AK Anchor tiles from Perfo UK are designed to be laid on top of existing grass, then rolled in and tested to withstand loads of 60 tonnes per square metre. As with all grass reinforcements, the load rating when laid will be dependent on the integrity of the ground on which they are being installed.

Sales director Chris Barcus says: "This is a first for this type of system. Tiles are clipped together on top of the grass and then rolled or compacted into the surface. Deep anchors featured on the tiles cut into the ground to resist movement."

This semi-closed design helps to prevent the resurgence of mud through the tiles and makes them more resistant to the turning effects of vehicles in soft ground. As no sub-base is required for normal applications, the system is quick and easy to install and the surface can be used immediately.

The 100 per cent recycled PE/PP tiles are ultraviolet and frost resistant and can also be installed in a gravel with or without sub-base. The top surface can then be back filled if required, either with gravel or soil, to promote grass growth.

Tenax marketing coordinator Kerry Davies reports that flexible grass protection mesh GP-FLEX has been offered by the company since early spring. Described as a new generation grass protection system, the profile of the mesh has been designed to increase slip resistance and it has been independently tested to BS 7976.

"The product is easy to install but the grass surface should be cut and any potholes filled prior to fitting," says Davies. "GP-FLEX is then rolled out and pinned down, allowing grass to grow through the profile. Ground conditions are important because the surface needs to drain well."

There are three grades available: 1000 is suitable for pedestrians, wheelchairs and occasional overflow parking; 1400 is suitable for light commercial vehicles and 4x4s; and 1800 is suitable for access routes for heavier vehicles, including HGVs.

Manufacturing in Devon, Source Control Systems produces SCS Integra, a modular unit that locks on all four sides and works in conjunction with neighbouring units. This has recently been used on a project for Gloucestershire County Council. The Netheridge Market site in Gloucester used 8,000sq m of Integra, which is manufactured from high/low-density polyethylene and has a compressive strength of 240 tonnes per square metre.

The product was selected because it is claimed to score well on grass growth - water can travel horizontally and vertically due to inter-cell connectors. Managing director Graham Martin-Loat says: "Water and grass go through from one cell to another in a continual matrix."

Commenting on one of the park-and-ride schemes undertaken by the company at Wilton and Salisbury, technical adviser Paul Vincent says: "Here the running bays are in hardstanding tarmac and the parking bays in SCS Integra filled with gravel. This means all surface water from the tarmac runs off into the parking bays and no additional drainage is required on the site."

Generally, for best infiltration SCS Integra is installed on a layer of clean stone. This lies on an appropriate geo-textile separation/filtration layer and beneath this a free-draining sub-base Type X is laid to a depth of 150-250mm, depending on designers' specification and application. All stones smaller than 3mm and fines are taken out to make sure it is free-draining. This is encapsulated in an appropriate geo-textile separation/filtration layer.

Where grass is required, the product is back-filled with good-quality topsoil and once settled, grass seed is sown to grow over. Grass is kept short by vehicle movement and requires minimal cutting when the surface is used regularly. Integra can be shaped to go around lamp posts and trees, even those with protection orders, and has recently been used in the Botanical Gardens in Cambridge around the Darwin trees.

Fleximas products include "premium turf reinforcement mesh", suitable for heavy pedestrian traffic and overflow car parks. For use on old or new turf, minimum site preparation is required and the surface can bear up to two tonnes per square metre. A heavy-duty version can be used for horse paths or car parking, up to vans, because it can bear up to eight tonnes per square metre.

For vehicle access, heavy pedestrian use and grass verges in urban and parkland areas, Fleximas Grass Reinforcement Mesh offers a long-lasting polymer grid to permanently reinforce grassed areas. It is vital that grass is allowed to grow and knit to the mesh for as long as possible because the area will then provide better protection. The best time to install is spring, when it will take two to three weeks to establish properly.

- Fleximas 01283 841800
- Lindum 01904 448675
- Perfo UK 01992 878152
- Rigby Taylor (Grass Seed) 0800 424919
- Source Control Systems 01283 509021
- Tenax 01978 66466

Modern turf technology tested

Tried and tested through all weather conditions, including very heavy rainfall, the cold winter of 2009 and the scorching early summer sun of 2010, Lindum's Lokturf has played an important role in providing durable paths at Wentworth Castle Gardens, where 2,700sq m have been used.

As this garden, based in Stainborough near Barnsley, is grade 1 registered and in a conservation area, it was necessary to restore pathways in a sympathetic way. Inside and outside areas next to the walls of the gothic folly, built by Thomas Wentworth in 1727, required reinforcement.

Lindum managing director Stephen Fell explains: "Lokturf is 40mm thick and produced by growing hard-wearing grasses in a polypropylene fibre, reinforced Loksand rootzone supplied by Tarmac Topsport. At Wentworth, the turf was then laid onto a rootzone of Loksand, 60mm deep, which gave a total reinforced depth of 100mm."

Estate manager Michael Klemperer adds: "It's enjoying the rain at the moment. We had around 40,000 visitors last year and we're expecting more than 50,000 this. We're applying for funding for phase two of the renovations and if we get the go-ahead we'll certainly consider using Lokturf for our large lawn area. We host a number of events - Much Ado About Nothing, A Midsummer Night's Dream - as well as car rallys and plant fairs."

Most paths follow historic routes but some had become quite overgrown and others needed to be completely reinstated. Reinforced turf was chosen over hard landscaping because of its aesthetic qualities.

Lindum is putting Lokturf down on a number of event areas at large stately homes and private estates as well as football pitches. Benefits include the fact that Lokturf is instantly usable and designed to withstand the rigours of heavy usage.

Grass selection

Are you selecting the correct grass seed formulation? Seed selection is very important where grass mixtures are to be used in reinforcement material. Climate change from north to south means it is vital to create mixes with different attributes, depending on site location.

An ideal formulation requires grass species that are drought tolerant and can recover rapidly after stress and heavy wear - because severe stress can be placed on the leaf structure.

A sward with high density is advisable because it will reduce the invasive weed grasses and other undesirable plants. Long-term maintenance requirements are also important and should be considered at the seed selection stage.

Rigby Taylor agronomist and seed director Brian Robinson suggests: "For lower maintenance, the aim should be to use species that create up to 40 to 50 per cent less volume of grass arisings because this reduces financial implications and CO2 emissions.

"Smooth-stalked meadow grass does not germinate very quickly so is not good for use in the north. It is also slow on recovery and has limited drought tolerance."

For verges, driveways and picnic areas with good recovery and density, Robinson suggests that perennial ryegrass should make up 45 per cent of the mix, slender creeping 35 per cent with 20 per cent strong creeping red fescue.

For access ways and areas where pressure is exerted on the grasses and the corresponding soil structure, the suggested mix is 20 per cent hard fescue, 25 per cent chewings fescue, 25 per cent slender creeping red fescue, 25 per cent strong creeping red fescue and five per cent browntop bent.

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