Key Takeaways:
- Land drainage systems are installed to help manage excess surface water.
- To extend the lifespan of your land drainage installation, wrapping the pipe and gravel with a non-woven white geotextile membrane is recommended to prevent silt buildup inside the pipe.
- The land drainage pipe must be surrounded by at least 150mm of gravel, so this should be considered when digging the trench.
There are a few things you should know before going ahead with fitting land drainage. It's crucial to understand how to properly connect the land drains and where they are best used, along with how the different types of pipes function. However, it’s difficult to grasp these concepts without first discussing the basics.
What Actually Is Land Drainage?
Land drainage is commonly used to relieve excess surface water. It's often referred to as a 'French drain' and consists of a flexible black pipe with a corrugated outer layer. These pipes come in perforated and unperforated varieties, each serving different purposes depending on the job requirements. At EasyMerchant, we stock sizes ranging from 60mm to 110mm for both perforated and unperforated land drainage pipe coils.
How Do the Land Drain Pipes Actually Drain Land?
Both types of land drainage pipes—perforated and unperforated—have their own uses. Perforated land drainage pipes are used to collect water from the ground. The small holes in the pipe allow groundwater to enter the pipe after passing through the soil above. This helps the water percolate back into the surrounding soil or be directed into an underground drainage system at a controlled rate, preventing long-term surface water accumulation. Land drain pipes are fully perforated, meaning the holes are all around the pipe, which improves field drainage efficiency.
Unperforated land drainage pipes are designed for distributing surface water. If you need to redirect water into another watercourse, such as a river or soakaway system, the unperforated pipe is typically the best choice. Just ensure that it is only used for surface water and not foul water, as this could violate regulations.
In What Situations Should You Use Land Drain?
There are various scenarios where land drainage is necessary. Building, landscaping, and agricultural projects often require land drainage solutions for a variety of reasons. For instance, in agricultural projects like field drainage, a perforated pipe is ideal and can improve soil quality. Similarly, this type of underground drainage is also used for sports fields and domestic areas.
Additionally, built-up areas must avoid becoming flooded with standing surface water. Excess water can increase the static load on structures below ground, compromising their structural integrity over time. This is why land drainage is vital in urban settings to prevent future water-related issues.
How to Identify a Land Drainage Pipe?
Most land drainage pipes used in projects are black. Be careful not to confuse them with black electrical ducting, which is black to indicate its contents. In contrast, land drainage pipes are black by default, but they serve entirely different functions.
Is There a Certain Way to Lay the Land Drainage Pipe?
Preparing to Lay the Land Drain:
If you're planning to install land drainage in a domestic setting, such as a garden, remember that any point within the area should be within 2.5 meters of the land drain. Often, people opt for the herringbone drainage layout, where a central spine pipe branches out using Y connections for each section of land drain. This maximizes coverage and provides the best drainage solution.
For larger areas, the 2.5-meter rule may not be the best approach. Additionally, ensure that there is only a slight fall for land drainage before installation. A slope of 1 in 150 is common, but it should never exceed 1 in 100.
The Actual Installation Process:
When starting any pipework job, we recommend working backward from your position, as it makes the task much simpler. The trench should accommodate about 150mm of granular material on each side of the pipe when installed.
The trench depth should allow for at least 100mm of bedding at the bottom. Additionally, it should also permit 150mm of gravel to cover the pipe, followed by 300mm of free-draining material. Finally, the trench will be filled with 100mm of previously excavated soil and can be covered with turf.
The trench depth depends on the pipe size, but for a common size like 100mm pipe, the trench would be approximately 750mm deep. Always consider the other layers with your pipe size to determine the appropriate trench depth.
Is the Use of Geotextile Membrane Essential When Installing a Land Drainage System?
While it's not absolutely necessary, using a non-woven geotextile membrane is advisable if you want your system to remain reliable and functional over a long period. It doesn't impede water flow but prevents silt and dirt from entering the pipework, thus extending the system's lifespan and reliability. If suitable for your project, the permeable geotextile membrane should be applied below the top layer of excavated soil but above the free-draining layer.
Ring Us If You Are Unsure!
There are several aspects to consider when installing land drainage, and sometimes it can get confusing. If anything in this article is unclear, don't hesitate to consult a drainage engineer or reach out to us—we’ll do our best to address your queries!
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