In the world of civil engineering and development approvals, hydraulic modelling is the language we use to speak to Council. But not all models are created equal.
Two names dominate the Australian stormwater landscape: DRAINS and TUFLOW. For developers and project managers, knowing the difference between these two software packages—and when to deploy them—can be the difference between a smooth DA approval and a project stuck in “Request for Information” (RFI) purgatory.
Here is a technical comparison of the two industry standards and how to choose the right engine for your project.
DRAINS: The Urban “Workhorse” (1D Modelling)
DRAINS is the industry standard for designing stormwater drainage systems in Australia. It is primarily a 1-Dimensional (1D) modelling package.
What it does best:
DRAINS excels at modelling what happens inside the pipes. It simulates how water moves from pits to pipes, through On-Site Detention (OSD) tanks, and out to the discharge point.
When we use it:
- OSD & Drainage Design: It is the go-to tool for sizing pits, pipes, and OSD storage volumes to meet Council’s “Permissible Site Discharge” (PSD) limits.
- Hydraulic Grade Line (HGL) Checks: Verifying that water won’t surge out of pits and flood the surface during a storm.
- Standard Urban Developments: For 90% of commercial and residential sites where the primary goal is capturing and controlling roof and hardstand runoff.
The Limitation: DRAINS assumes water flows in a defined line (like a pipe). It struggles to accurately model complex “overland flow” once water escapes the pipe and spreads across a landscape.
TUFLOW: The “Heavy Lifter” (2D Modelling)
TUFLOW is a sophisticated 2-Dimensional (2D) computational engine. It simulates water moving over a terrain surface (a Digital Elevation Model), calculating velocity and depth in every direction across a grid.
What it does best:
TUFLOW visualises flood behaviour. It shows exactly where water goes when it hits a building, flows down a driveway, or spills out of a creek. It produces the “Flood Maps” you often see in Council studies.
When we use it:
- Flood Prone Land: If your site is tagged as “Flood Prone” or is near a creek/overland flow path, Council will likely demand a Flood Impact Assessment using 2D modelling.
- Complex Overland Flow: Proving that your new building won’t divert floodwater into your neighbour’s property (an actionable nuisance).
- Basement Entries: Determining the exact “Freeboard” level required for driveway humps to prevent basement flooding.
The Cost: TUFLOW is more data-intensive and computationally expensive than DRAINS. It requires detailed survey data and significant engineering time to build and run.
Which One Do You Need?
Choosing the wrong model can be costly. Using TUFLOW for a simple pipe design is overkill and wastes budget. Using DRAINS for a complex flood site will likely result in Council rejecting your DA for “insufficient analysis.”
| Feature | DRAINS (1D) | TUFLOW (2D) |
| Primary Focus | Pipes, Pits, OSD Tanks | Flood Plains, Overland Flow, Creeks |
| Output | Hydrographs, Pipe Capacities | Flood Maps, Velocity Vectors, Hazard Zones |
| Complexity | Low to Medium | High |
| Cost | Lower | Higher |
| Best For | Standard DA/CC Stormwater Design | Flood Risk Assessments & Rezoning |
The Strategic Advantage: Integrated Modelling
At Stormwater Services Australia, we don’t just pick one. For complex projects, we often use an integrated approach.
We use TUFLOW to define the boundary flood levels and overland flow risks to set the finished floor levels. Then, we use DRAINS to value-engineer the internal pit and pipe network for maximum efficiency.
By having both capabilities in-house, we ensure your project isn’t held up by a consultant who only has half the toolkit. We select the method that provides the fastest path to DA approval with the most defensible data.
Is your project on flood-prone land?
[Contact Our Engineering Team] for a strategic review. We will advise whether a 1D or 2D model is required to de-risk your development application.
