A well-installed land drainage system is the ideal solution for any grassy areas that tend to become waterlogged, no matter if they're in a domestic, commercial, industrial, or agricultural setting. This is especially true in the UK, where we face a fair amount of rainfall annually, even during the warmer months. Areas with dense clay soil or those located near large bodies of water are particularly prone to this issue. Waterlogging can be both time-consuming and costly to address, as it can severely damage landscapes, gardens, plants, and even building foundations. However, with a well-designed land drainage system, you can avoid these problems entirely. Not only is it an effective way to prevent flooding, standing water, and property damage, but land drainage systems are also relatively affordable—especially when compared to the costs of repairing ongoing flood damage—and straightforward to install.
As with most solutions, there are various approaches you can take when installing a land drainage system. Among them, the classic herringbone design remains one of the most popular choices. There are several reasons for its popularity, which we’ll discuss here, along with a brief overview of alternative land drainage layouts you might want to consider if surface water is an issue. In this article, we'll also provide a quick overview of how land drains work to solve drainage problems and share practical tips and information on installing a reliable herringbone drainage system.
Key Takeaways:
- Land drainage systems help prevent waterlogging and flooding in grassy areas.
- Land drains are perforated PVC pipes placed in trenches and covered with aggregate, allowing excess rainwater to seep into the pipes and flow toward designated disposal points.
- Common land drainage system layouts include the herringbone, linear, cross-drain, and sump-and-pump systems.
How Land Drains Work:
Land drains are perforated PVC pipes that are installed in prepared trenches across areas where rainwater collection is a problem. When secured between layers of aggregate—such as gravel or stone chippings—the excess rainwater can slowly seep into the pipes through the perforations. Provided the pipes are installed at a sloping gradient, the collected water can flow smoothly to disposal points like storm drains, soakaway crates, or natural water sources such as rivers or lakes.
Land drains have been a tried-and-tested method of water removal since the 19th century and are sometimes called French drainage systems, named after Henry Flagg French, the American farmer who popularized them. Back then, simple roofing tiles were used, but today, all land drainage piping is made from durable PVC, which resists water erosion and comes in various lengths and diameters. Depending on the application, either flexible land drain coils or stronger twin-wall land drains are used. The former is easier to transport and install, while the latter is ideal for high-pressure environments like highways, railways, and airports.
Drainage System Options:
Although all pipe drainage systems operate similarly, there are different layouts to suit various shapes and areas. Here are the four most commonly used:
Herringbone System:
The herringbone system involves a central pipe installed on a downward slope, with lateral pipes connected at slight angles. The resulting pattern resembles a herring fish's bones, hence the name. Instead of relying on a single trench, this method creates multiple trenches sloping toward the main pipe for efficient drainage. This system is ideal for larger areas like sports fields, golf greens, and irregularly shaped domestic or commercial lawns.
Grid System:
Also known as a gridiron or parallel drainage system, the grid layout consists of a main pipe running along the perimeter of the area needing drainage, with lateral pipes crossing the area and connecting at right or acute angles. This system works best for uniform, geometric shapes such as football pitches, rugby grounds, and bowling greens. It is frequently used on turfed areas due to its ease of installation, and sand or gravel slits can be added with minimal disruption to playing fields.
Fan System:
The fan system is often used in small gardens, low-lying wet areas, or oddly shaped lawns. It can also be useful for golf fairways, though the herringbone pattern is better suited for larger golf greens. To create a fan drainage system, several lateral pipes are evenly spread out and connected directly to an outlet.
Natural System:
Sometimes called a contour or random drainage system, the natural system follows the contours of the ground beneath it, with the piping laid to echo the natural curves of the land. This system is best suited for amenity grasslands, such as sports grounds, village greens, and park lawns.
Pros and Cons of the Herringbone Pattern:
While the herringbone pattern can be slightly more expensive to install due to the amount of piping required, it remains popular because the trenches don't need to be as deep as those in other systems, saving time. Its main advantage lies in its efficiency, ensuring good drainage coverage across large areas. It is recommended that no part of a lawn or turf area needing drainage be further than 2.5 meters from a section of pipe.
One downside of the herringbone pattern is that it can be trickier to install than other systems, but this can be mitigated with a clear and accurate plan.
Installation Advice:
Regardless of the pattern you choose, the installation process is similar and requires only a few items and tools. These include perforated land drainage pipe coils, land drain couplers, multi-junctions, a saw for cutting pipe lengths, suitable gravel, topsoil, non-woven geotextile membrane, and digging equipment. While the exact steps may vary based on your method and tools, the general process involves six key stages:
Planning and Preparation:
Before starting, create a visual plan to ensure you have enough land drain pipes for the area and know the lengths and trench locations. A basic plan can serve as a helpful guide throughout the process. Additionally, consult with local authorities regarding disposal points for collected rainwater, as councils typically own storm drains. If redirecting water to a natural source like a river or lake, you may need permission from the Environment Agency.
Trench Digging:
Ensure your trenches allow enough space for the pipes and aggregate. Experts suggest allowing 15 cm of gravel backfill on each side of the pipes, a minimum of 45 cm depth (15 cm of topsoil and 30 cm of drainage layer), and around 10 cm of gravel at the trench base. Adjust depth based on soil type and pipe size, but trenches deeper than 120 cm should be shored to prevent collapse.
Laying Geotextile:
Install non-woven geotextile membrane to protect the system from sediment buildup. This lightweight separator allows water to pass through while blocking soil, stones, and other materials that could cause blockages. Custom-sized geotextile can be ordered to avoid waste.
Laying Drains:
After laying geotextile in the trenches, create a 10 cm deep gravel base. Carefully add the drains, using connectors to join lengths and multi-junctions to link lateral pipes. Ensure the pipes are installed at a gradient of approximately 1:150 for steady water flow. Avoid placing perforated pipes incorrectly, as the perforations should face downward.
Adding in Backfill:
Fill trenches with at least 30 cm of gravel, leaving 15 cm from the surface. Use small crushed stone for optimal drainage, avoiding decorative gravels that may trap water.
Covering Land Drains:
Once drains and aggregate are in place, cover with geotextile and topsoil, finishing with grass.
New Drainage Planks:
Enviroflow drainage planks, a 100% recycled product, are easy to install and never clog. They are 1-meter sections that can be placed in trenches and covered. Ideal for smaller projects, they don’t dry like pipework, leaving no lines in the grass.
Specialist Drainage Products:
For lasting solutions, use commercial-grade products. EasyMerchant offers flexible, tough, and easy-to-install land drainage supplies, including channel drains for patios and landscaped areas. All products are from leading manufacturers, many with the British Kitemark, ensuring quality. Orders ship within 1-3 business days, and our customer service team is available for advice.
In conclusion, a well-thought-out land drainage system is essential for maintaining healthy grassy areas and preventing costly water damage. Whether you choose the herringbone or another layout, proper planning and execution are key to achieving long-term success.
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