Land drains
Encyclopedia
The purpose of a land drain is to allow water in wet or swampy ground to rapidly drain away or to relieve hydrostatic pressure. They are subterranean linear structures which are laid to a fall which should be as steep as practicable. They are used in agriculture and in building construction sites. Modern land drains take the form of a perforated or discontinuous (i.e. open-jointed) pipe. Typically, the land drains conduct the surplus water to an open ditch or natural water source.
soils and peat
s by excavating a trench and forming a "tunnel" using flat stones, this was very labour intensive but could be often be done using free materials to hand. Typically they were two to three feet (600mm-900mm) below the surface. Agricultural land drains have to be installed sufficiently deep to avoid plough
damage. Later short earthenware
pipes were used laid edge to edge. These are still used. These can be laid in an excavated trench, more usually these days, a horizontal hole is formed in the ground using a mole plough and the pipes are forced in by means of a hand or mechanical press. By this means, heavy wet soils, bogs and swamps could be rendered amendable to agriculture. Virtually all crops need a well drained soil to grow well.
material can surround the gravel to keep out silt. This can be installed in an excavated trench. Specialised mole plough
s are available that can form the hole, insert the perforated pipe (and gravel if required), all in one simultaneous and continuous process. An extremely powerful (usually tracked) tractor
is necessary. The flexible pipe is carried as a roll on the back of the machine. There is a sometimes a hopper
for gravel which is kept topped up by an adjacent machine. The pipe and gravel go down apertures in the plough blade as the tractor proceeds along the desired route.
material which filters out soil particles. Ideally, land drains are laid with access points so that high pressure water jetting is possible to clear silt. However, whatever the technology, all land drains have a finite life and eventually become ineffective due to the ingress of silt and/or the blocking of the surrounding filter media.
In agriculture
Traditionally, land drains were formed in clayClay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
soils and peat
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...
s by excavating a trench and forming a "tunnel" using flat stones, this was very labour intensive but could be often be done using free materials to hand. Typically they were two to three feet (600mm-900mm) below the surface. Agricultural land drains have to be installed sufficiently deep to avoid plough
Plough
The plough or plow is a tool used in farming for initial cultivation of soil in preparation for sowing seed or planting. It has been a basic instrument for most of recorded history, and represents one of the major advances in agriculture...
damage. Later short earthenware
Earthenware
Earthenware is a common ceramic material, which is used extensively for pottery tableware and decorative objects.-Types of earthenware:Although body formulations vary between countries and even between individual makers, a generic composition is 25% ball clay, 28% kaolin, 32% quartz, and 15%...
pipes were used laid edge to edge. These are still used. These can be laid in an excavated trench, more usually these days, a horizontal hole is formed in the ground using a mole plough and the pipes are forced in by means of a hand or mechanical press. By this means, heavy wet soils, bogs and swamps could be rendered amendable to agriculture. Virtually all crops need a well drained soil to grow well.
Modern land drains
Many modern land drains are created utilising rigid or flexible plastic pipes pierced with holes, laid in pea gravel. (The pea gravel is pea sized pebbles without sharp points to damage to pipe.) GeotextileGeotextile
Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain...
material can surround the gravel to keep out silt. This can be installed in an excavated trench. Specialised mole plough
Plough
The plough or plow is a tool used in farming for initial cultivation of soil in preparation for sowing seed or planting. It has been a basic instrument for most of recorded history, and represents one of the major advances in agriculture...
s are available that can form the hole, insert the perforated pipe (and gravel if required), all in one simultaneous and continuous process. An extremely powerful (usually tracked) tractor
Tractor
A tractor is a vehicle specifically designed to deliver a high tractive effort at slow speeds, for the purposes of hauling a trailer or machinery used in agriculture or construction...
is necessary. The flexible pipe is carried as a roll on the back of the machine. There is a sometimes a hopper
Hopper
Hopper may refer to:-Mechanical parts:* A general term for a chute with additional width and depth for temporary storage* Hopper , a large container used for dust collection* Part of a combine harvester...
for gravel which is kept topped up by an adjacent machine. The pipe and gravel go down apertures in the plough blade as the tractor proceeds along the desired route.
In building construction
The purpose of land drains in building construction is somewhat different. If voids are created in the ground for any reason they tend to fill with water. Also the static loads on any subterranean structure and retaining walls can be massively increased by the presence of water in the surrounding ground. Land drains are introduced to relieve this pressure. Traditionally, the drains were created by backfilling behind retaining walls etc. with rubble and allowing the water to drain through the rubble to some suitable point.As part of highway construction
Instead of having open ditches at the side of highways, land drains can be installed. The excavated trenches are completely filled with gravel (i.e., no soil cover). This is far safer than open trenches if a vehicle should run off the highway.Problems
Holes or gaps have to be left in the pipes to allow water to transfer from the subsoil to the pipe and these tend to block with soil or allow silt into the pipe, so blocking it or reducing the flow of water. This can be partially overcome by surrounding the pipes with gravel. However, with time even the gravel becomes choked with soil/silt, so in the latest practice, the gravel is surrounded with a geotextileGeotextile
Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain...
material which filters out soil particles. Ideally, land drains are laid with access points so that high pressure water jetting is possible to clear silt. However, whatever the technology, all land drains have a finite life and eventually become ineffective due to the ingress of silt and/or the blocking of the surrounding filter media.