What Is an Agi Drain?

An agricultural drain, commonly called an Agi drain, is one of the most important parts of a retaining wall.

Although it’s completely hidden once construction is finished, it plays a critical role in protecting the wall by collecting groundwater and directing it safely away from the structure.

At Crawfords Fencing, we believe an Agi drain isn’t an optional extra—it’s an essential part of building a retaining wall designed to last.

Why Is an Agi Drain Needed?

Rainwater naturally soaks through soil.

Without a drainage system, that water becomes trapped behind the retaining wall.

As the water builds up, it creates hydrostatic pressure, placing enormous force against the wall.

As Director Tyrone Crawford often tells clients:

“A retaining wall is designed to hold back dirt—not a swimming pool.”

Without somewhere for the water to go, that pressure continues increasing until something eventually gives.

How Does an Agi Drain Work?

An Agi drain is a perforated pipe installed behind the retaining wall, usually at the base of the excavation.

Water enters the perforations in the pipe and is carried safely to a suitable discharge point before pressure has a chance to build behind the wall.

An Agi Drain Doesn’t Work Alone

A pipe by itself isn’t enough.

A proper drainage system works as one complete system.

Depending on the project, we commonly install:

• Agricultural drainage pipe.

• Free-draining scoria.

• Geotextile drainage fabric.

• Suitable drainage outlets.

Every component has a purpose.

If one component is missing, the entire drainage system becomes less effective.

Why We Use Scoria

Scoria provides open spaces that allow water to move freely towards the Agi drain.

Unlike ordinary soil, it doesn’t trap water against the retaining wall.

Combined with geotextile fabric, it creates an efficient drainage zone behind the wall.

Why We Use Geotextile Fabric

Without geotextile fabric, fine soil particles gradually wash into the scoria.

Eventually those voids fill with dirt, reducing drainage performance.

Think of geotextile fabric like a coffee filter.

It allows water through while keeping the soil where it belongs.

What Happens Without an Agi Drain?

Retaining walls built without proper drainage commonly experience:

• Water pressure.

• Bowing.

• Leaning.

• Cracking.

• Premature structural failure.

• Expensive repairs.

Most retaining wall failures begin behind the wall, long before they’re visible from the front.

It’s One of the Cheapest Parts of the Job

Compared to the overall cost of a retaining wall, installing proper drainage is relatively inexpensive.

However, it provides one of the biggest returns in long-term performance.

Trying to save money by leaving out the drainage system is one of the most expensive shortcuts a contractor can take.

Our Philosophy

At Crawfords Fencing, we don’t build retaining walls that simply look good on handover.

We build retaining walls designed to perform for decades.

As Director Tyrone Crawford often says:

“You’ll never see the Agi drain again once the wall is finished—but it’s one of the hardest-working parts of the entire job.”

Build It Once. Build It Properly.

A retaining wall is only as strong as the system behind it.

Proper drainage protects your investment, reduces long-term maintenance and dramatically improves the lifespan of the wall.

That’s why every Crawfords Fencing retaining wall is designed with drainage in mind.

Need a Retaining Wall Built to Last?

Whether you’re building a timber sleeper retaining wall, concrete sleeper retaining wall or one of our specialist bolt-on integrated retaining wall and fence systems, Crawfords Fencing has the experience to build it properly from the ground up.

We proudly service Ringwood, Croydon, Heathmont, Blackburn, Mitcham, Doncaster, Lilydale, Mooroolbark, Yarra Glen and surrounding suburbs throughout Maroondah, Whitehorse, Manningham, Knox and the Yarra Ranges.

Contact Crawfords Fencing today for a free, no-obligation quote.