Stormwater Pits

What A Stormwater Pit Does

A stormwater pit has three main jobs:

Collect runoff

It intercepts surface water from roofs (via downpipes), paved areas (driveways and patios), and ground runoff (yards and landscaped areas).

Trap debris before it enters the pipe network

Leaves, silt, grit, mulch, and rubbish often get washed into pits. A properly built pit acts as a first defence so the pipework is less likely to block.

Move water to a legal point of discharge

Once collected, water flows out through the pit outlet into stormwater pipes and onward to the kerb and channel, council stormwater, an approved easement, or another lawful discharge point (depending on site setup and local requirements).

How Stormwater Pits Work

1) Water enters through a grate or inlet

Most pits have a grate on top. Water drops through the grate into the pit below. Some pits also have side entries that let water flow in from the surface, especially in driveway or yard drain setups.

2) The pit acts like a small holding chamber

Inside the pit there is usually a sump area (space below the outlet) where heavier debris settles. This helps stop silt and gravel from constantly washing into the pipes.

3) Water exits through the outlet pipe

The outlet pipe is connected to the stormwater line. The outlet height is set so sediment can settle below it, and the pipe size is matched to expected flow.

4) Gravity does the work (when levels are correct)

A stormwater system relies on correct fall (slope). If the pipe run is too flat, undersized, poorly joined, or backfalling, pits will hold water and overflow in heavy rain.

Common Types Of Stormwater Pits

Grated inlet pits

Most common on properties - a square or rectangular pit with a grate lid, used to capture surface water.

Downpipe connected pits

A pit that receives roof water directly from downpipes. This is useful where multiple downpipes are being combined, or where you want a debris trap before the stormwater line.

Strip drains with a pit outlet

A trench drain (channel drain) feeds into a pit, which then connects to stormwater pipework. Common across driveways, pool surrounds and alfresco areas.

Junction pits

Used to join multiple stormwater lines together, change direction, or transition to a different pipe size.

Kerb adaptor pits / kerb outlets

Where allowed, some properties discharge to the street kerb and channel via a kerb adaptor connection. These must be installed correctly and meet local rules.

What Is Inside A Pit?

A well-built pit is more than a hole in the ground:

• Solid base (so it does not sink or wash out)
• Correct inlet configuration (grate, side entry, downpipe inlet)
• Sump space (to collect silt and debris)
• Correct outlet height (so debris settles below the outlet)
• Sealed penetrations (to stop soil migration and washouts)
• Traffic-rated lid if required (driveways need lids designed for vehicle loads)

If any of these are wrong, you can end up with ongoing blockages, subsidence, cracked pipes, or pits that collapse over time.

Why Stormwater Pits Block Or Fail

Stormwater issues are usually caused by a combination of debris load and poor design or ageing infrastructure.

Common problems include:

• Leaves and garden debris washing in
• Silt and sand build-up after rain events or landscaping work
• Tree roots entering cracked stormwater pipes downstream
• Broken or collapsed pipes causing water to back up into the pit
• Incorrect fall / backfall from poor installation or ground movement
• Undersized pipework that cannot handle heavy rainfall
• Grate sits too high or too low causing surface pooling or erosion around the pit
• Illegal or poor discharge point leading to constant surcharge and overflow

Warning Signs Your Stormwater Pit Needs Attention

If you notice any of the below, it is time to get it checked:

• Water ponding around the pit instead of draining quickly
• The pit holds water for hours or days after rain (often a sign of blockage, poor fall, or downstream failure)
• Overflow during moderate rain, not just storms
• Bad smells (can indicate cross-connection issues or stagnant water)
• Sinking pavers or soil around the pit (washout or collapse)
• Visible cracks in the pit walls or loose lid
• Downpipes gurgling or overflowing (roof water not clearing)

How Plumbers Diagnose Stormwater Pit Problems

Stormwater is a system - not just the pit. A proper diagnosis often includes:

• Visual inspection of the pit, grate, and inlet points
• Checking outlet condition and flow
• CCTV drain camera inspection of the stormwater line to find cracks, roots, sags, or collapses
• Testing fall and flow to confirm drainage performance
• Locating the point of discharge to make sure it is functioning and compliant
• Identifying contributing factors like landscaping runoff, leaf load, or poor capture areas
• This is where plumbing expertise matters: you want the cause fixed, not just the symptoms cleared.

Stormwater Pit Maintenance - What Actually Works

Good pit maintenance is simple, but it needs to be done properly:

Regular debris removal

Clear leaves, mulch and sediment from the grate and sump area, especially before storm season.

High-pressure drain cleaning

If the line is silting up or partially blocked, jetting can restore flow and flush built-up debris out to the discharge point.

Camera checks for recurring issues

If a pit keeps blocking, there is usually a structural reason - cracked pipes, root intrusion, or an incorrect grade.

Lid and grate checks

Driveway lids must be secure and correctly rated. Broken grates are a safety risk and can allow larger debris into the system.

Prevention upgrades

Simple upgrades can reduce ongoing problems, like installing a better debris basket, improving capture with strip drains, or adding an additional pit where water is pooling.

Can Plumbers Build New Stormwater Pits And Systems?

Yes - and it is often the best long-term fix when a property has chronic pooling, flooding, or damaged stormwater lines.

Professional stormwater pit work can include:

• Designing pit locations to intercept runoff where it naturally flows
• Installing new stormwater pits with correct base, sump depth, and fittings
• Connecting downpipes into pit and pipe networks (including overflow management)
• Installing new stormwater pipe runs with correct fall and appropriate pipe sizing
• Replacing broken pits and rebuilding surrounds to prevent washouts
• Integrating strip drains for driveways, patios, garages, and pool areas
• Upgrading discharge points so water leaves the property safely and legally

Done properly, these upgrades protect your home, landscaping, and hardscapes - and reduce the risk of foundation moisture issues.

Why Using A Qualified Plumber Matters

Stormwater looks straightforward, but it is easy to get wrong. A plumber experienced in drainage understands:

• How rainfall runoff behaves across different surfaces
• How to size and grade stormwater pipework for proper flow
• How to prevent silt and debris from constantly blocking lines
• How to locate and repair collapsed or root-invaded pipes
• How to build pits that do not sink, crack, or wash out
• How to keep the system serviceable for long-term maintenance

If stormwater is not handled correctly, you can end up with repeated flooding, expensive landscaping repairs, and long-term moisture problems around the property.

When To Call A Plumber For Stormwater Pits

You should bring in a plumber if:

• Your yard or driveway floods or stays wet after rain
• The pit overflows, blocks regularly, or always holds water
• You suspect broken pipes, tree roots, or collapse
• You want to add a new pit, connect downpipes, or install strip drains
• You are renovating outdoor areas and want drainage done properly the first time

Need Stormwater Pit Help?

As plumbers, stormwater pits are right in our wheelhouse. We can inspect, clear, repair, rebuild, and install stormwater pits and the pipework connected to them - and we can also set up a maintenance approach that stops the same issue coming back every time it rains.