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Things to Consider When Choosing a Subsurface Drainage System

It’s imperative to choose the right drainage system for specific soil types since their different characteristics need different drainage methods. Research has found that some farmers aren’t sure of their soil’s characteristics and can’t, therefore, determine which drainage method is perfectly suited to their soils.

Typically, subsurface drainage is attainable through subsurface pipes or mole drainage. To choose the best subsurface drainage system for your particular soil type, its characteristics, permeability, and clay content must be investigated. The soil’s hydraulic conductivity is also valuable for picking the right drainage system.

So, How Do You Pick The Right Drainage System?

When selecting a subsurface drainage system, there are several things to take into consideration. These include the soil’s texture, type of clay, as well as permeability. Even more, the soil’s physical characteristics should be determined. For instance, you should establish how deep an impermeable layer is located, the amount of profile that’s permeable, and the possibility of the soil to collapse or erode when excessively wet.

It’s therefore important to understand the soil type and profile so as to determine the type of subsurface drainage system that’s most appropriate. Testing involves analyzing soil cores so as to determine the soil types that are below the surface. By carefully examining the soil profile as well as measuring the soil’s permeability, you’ll be able to select the best drainage method.

Knowing the possible location and outfall level can also go a long way in helping you choose the perfect drainage system. If there isn’t a suitable outfall, then drainage won’t be possible unless very complex sumps and pumps are utilized. The gradient of your land can also have a significant impact on the drainage type plus its design.

Using the practical on-farm tests to examine the soil can really help you choose an excellent subsurface drainage system. These tests should address the following questions to help you make an informed decision:

Is the soil convenient for subsurface pipe drainage?

For subsurface pipe drainage, the soils must be highly permeable and free draining. There should be sufficient depths of up to 1m as well as enough gradient or fall to allow a convenient slope for the fitted drain pipe.

The outfall should be positioned in a way that allows this to effectively occur. Though slotted pipe drains tend to be more efficient in permeable soils, the spacing of pipes would have to be too close on impermeable soils causing them to be uneconomical on their own.

Is the soil well-suited for mole drains?

Soils that are suitable for mole drainage should contain a significant proportion of clay content deep down to a moling depth of 400 to 600 mm. It should also feature minimal rock as well as sand at a mole drainage depth. Most clay minerals will allow the mole channel to retain its original shape after moling. When it’s wetted up during drainage, the mole channel won’t collapse or become dispersive. Plus, it won’t be vulnerable to tunnel erosion. Nonetheless, certain types aren’t well-suited for mole drainage and could result in severe erosion is mole drained.

Is the soil appropriate for gravel mole drains?

These types of soils aren’t usually suited to mole drainage. In fact, they might end up slaking after wetting up or might contain sandy and rocky layers. Inserting permeable backfill through a specially designed gravel mole drainer deep into the mole slots will maintain the channel’s integrity paving way for the removal of drain water.

Different Types of On-Farm Tests

The following are some on-farm tests that farmers and contractors perform to ascertain which drainage method is best suited to specific soil types to be drained. They’re best done during winter when the soil is saturated. Nevertheless, you can choose to perform the same tests in dry conditions but with the help of EasyMerchant’s land drainage products.

If the tests aren’t decisive, proper on-farm soil tests conducted by a reputable laboratory should be utilized to evaluate the soil’s permeability, texture, as well as suitability for mole drainage. You may also want to consider consulting a subsurface drainage expert in the designing stage to help you select the perfect system and develop a viable drainage plan.

Ring Test

This test will establish the clay content and indicate the possible presence of sand as well as other small stones. Take the soil sample and roll it between your palms to form a rod-like shape of about 10 mm (diameter) and a length of 50 mm. Try bringing the ends together and ensure that the ring formed measures 50 millimeters in diameter. If it’s hard forming the ring, then the soil won’t probably be able to hold a molded drain since its clay content won’t be great enough to withstand a mole channel. And if it’s easily formed, the clay content is high and perfectly suited to moling.

Ribbon Test

Alternatively, you could squeeze the rod formed in the ring test between your thumb and forefinger creating a ribbon that features a width of approximately 10 to 13 millimeters and a thickness of about 5 millimeters. If a ribbon longer than 40 millimeters can be formed, it means that the soil features a high clay content. And if it continually breaks, then its clay content might be too low for mole draining. You could as well check for slaking and dispersion using the ball test.

Ball test

Typically, the ball test indicates if the soil is susceptible to slaking or dispersion. Plus, it also determines its ability to sustain the mole channel shape.

Slaking refers to the breakdown of soil aggregates into tinier particles when wet and involves the indication of low organic matter in specific soil samples.

Dispersion, on the other hand, is an indicator of sodic soils. It usually occurs when excess sodium is present in the soil. When some water is added, the sodium will attach to the clay’s negatively charged particles. And since this is a weak bond, the clay particles are pushed apart. This, in turn, results in the formation of a clay colloid clouds around the aggregate. These soils can be vulnerable to a tunnel as well as gully erosion if they’re mismanaged. Plus, they’re usually difficult to drain safely.


With all the above tips and tricks, you’ll find it easy choosing the right subsurface drainage system for your land. Different on-farm tests can always be performed to determine the suitability of your soil for various drainage systems.


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Written by Nat Sauteed

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