Drainage is one of the few jobs where the trench matters as much as the pipe. A line laid to a consistent fall in a properly bedded trench drains for decades. The same pipe in a trench with a flat spot in it holds water, silts up, and quietly stops working somewhere around year three.
What we do
- Agricultural (subsoil) drains — slotted pipe in an aggregate-filled trench, wrapped in geotextile, to drain a waterlogged lawn or garden bed.
- Stormwater trenching — trench excavation, bedding, pipe laying, backfill and compaction for surface and roof water runs.
- Water supply trenching — runs out to a shed, a tank, a tap or an irrigation system.
- Trenching for licensed plumbers — the excavation half of the job, so the plumber turns up to an open trench at the right depth and fall instead of spending their day on a shovel.
- Soakwells and rubble pits — excavation for on-site absorption where discharging elsewhere is not an option.
- Backfill and compaction — done in layers, so the ground does not sink into a channel across your lawn over the following winter.
Where the licensed plumber comes in
In Victoria, below-ground stormwater drainage work — from the above-ground pipes through to the point of discharge — is licensed drainage work under Part 4 of the Plumbing Regulations 2018, and the Victorian Building Authority requires it to be carried out by a licensed plumber. There is no owner-builder route around it.
So the split on a stormwater job is: we do the excavation, trenching, bedding, backfill and compaction, and a licensed plumber does the licensed work. If you have a plumber, we work to their setout. If you do not, we can point you at someone who does this regularly. Nobody should be offering to do the whole thing without a licence, and it is worth asking any quote you receive which side of that line it sits on.
Ag drain or stormwater?
These get confused constantly, and installing the wrong one is the most common drainage mistake we get called out to fix.
- Stormwater pipe
- Sealed. Carries roof and surface water away to a legal point of discharge. Keeps water out of the ground.
- Ag drain
- Slotted and porous. Sits in gravel wrapped in geotextile and is designed to let groundwater in, then carry it away. Drains a saturated lawn.
If your problem is a downpipe dumping into a garden bed, that is stormwater. If your problem is a lawn that stays spongy for a week after rain with no obvious source, that is groundwater sitting on clay, and it needs an ag line. The full explanation is in ag drain or stormwater?
Why Melbourne’s north waterlogs
Heavy clay subsoil, mostly. Rain soaks down through the topsoil, reaches a clay layer it cannot pass through, and stops. The water has nowhere to go but sideways and slowly, so it sits in the root zone. The lawn goes spongy underfoot, grass thins out and moss moves in, and it stays that way well after the rain has finished.
Nothing is broken — there is simply no path out. An ag line provides one.
What a properly built ag line looks like
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Trench cut to a consistent fall
Fall matters more than depth. A deep trench with a low spot in the middle is a buried puddle. The line has to run downhill the whole way to its outlet.
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Bedded in clean angular aggregate
Scoria or a clean crushed rock. Angular, because it locks together and keeps voids open for water to move through. Not sand, and not the crusher dust that turns to concrete.
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Wrapped in geotextile
The fabric is not optional and it is the first thing skipped on a cheap job. It stops fine clay particles migrating into the aggregate. Without it, silt fills the voids, the line chokes, and in about three years you are digging it up again.
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Outlet sorted before the trench is dug
An ag line has to discharge somewhere legal — a stormwater connection made by a licensed plumber, a soakwell, or a surface point that does not send water onto a neighbour. Work this out first. A drain with nowhere to go is a very tidy trench full of water.
Services get located first
Every job that breaks ground starts with a free Before You Dig Australia request. It puts the query in front of every registered utility with assets near the site and the plans usually come back in minutes. They show approximate locations, not exact ones, so anything near a marked service still gets located by hand before a bucket goes near it.