Land Drainage





Land Drains

 

An increasing amount of the Company’s work is the installation of land drains. The need for better drainage in a garden is obvious during winter or times of heavy rain. Patches of water appear on the surface and do not drain away as quickly as expected. Most water logged gardens, following a heavy rain fall, will drain away within 24 hours. In severe cases gardens or areas of gardens can remain flooded for days, or even weeks.

 

There are several reasons for this. The ground on which the building has been constructed may have been compacted during the building work; the land may have been agricultural and have an impervious layer just below the old ploughing level; the sub soil may be clay; or the land may have a shallow water table.

 

In some cases the top soil may be very water retentive and can be stripped away and replaced by organic material and new soil. If the problem is worse than this easy solution, some form of drainage is required.

 

Installing land drains means digging trenches and laying plastic pipes, which take the excess water to either a soakaway; a natural water course, such as a stream; or the rainwater drain from the house. The plastic pipe has a series of holes cut into the top half of the pipe. They are laid in a trench, the depth of which is determined by where the water will eventually run. This can be several feet or, occasionally, a few centimetres beneath the surface.

 

The trench is lined with pea gravel and the pipe laid in it, with a gentle fall in the direction away from the flooded area. The pipe is covered with a geotextile material, which allows the water to penetrate but keeps out soil and grit, which will clog the pipe.

 

Where large areas of a garden are flooded a “herring bone” pattern is used, so that the pipes are never less than 2.5 metres apart. When the pipe has been laid the ground can be returned to its desired purpose, lawn, beds, or vegetable/flower gardens.

 

If a soakaway is used, a large area is required to install the pit, which will be at least 2 metres deep and several metres square. It is filled with rubble and covered with geotextile material and about 300 mm of soil. Ideally, the pit will be deep enough to find a porous layer of ground which allows the excess water to soak away. If a porous layer cannot be found, the pit will need to be drained by pipe to a natural watercourse or the rainwater drains.

 

This arrangement allows the soakaway to be used as a storage tank at times of water shortage or drought. For a relatively low cost a submersible pump can be installed in an inspection chamber and a stand pipe fitted to the pipe taking the water away. By inserting a stop tap in the pipe the water can be used to water garden plants during any water restriction and save mains water, especially economic where a water meter is fitted to the house.

 

The cost of installing land drains is impossible to quantify without onsite inspection. There are many variables to consider and costs can range from low to high.




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