TUFLOW vs HEC-RAS vs Flood Modeller: Which Software When?

Flood modelling software is a tool, not a religion — though you would not always know it from the strength of opinion among modellers. Each of the three main packages used in UK practice has genuine strengths and legitimate use cases, and choosing the right software for a given project is a decision that should be driven by the project requirements, not personal preference.

This article provides a practical comparison of TUFLOW, HEC-RAS, and Flood Modeller Pro — the three flood modelling packages most commonly used for UK planning applications. We cover what each does well, where each has limitations, and how to choose the right tool for your project.

TUFLOW

Overview

TUFLOW is a 2D hydrodynamic modelling engine developed by BMT. It is widely regarded as the industry standard for 2D flood modelling in the UK, particularly for surface water (direct rainfall) modelling and floodplain mapping. TUFLOW uses a structured or flexible mesh grid to solve the 2D shallow water equations across the terrain surface.

Strengths

• 2D surface water modelling. TUFLOW is the dominant tool for direct rainfall modelling in UK practice. Its ability to apply rainfall directly to a 2D terrain grid and model the resulting overland flow makes it ideal for assessing surface water flood risk at site-specific resolution.
• High-resolution floodplain modelling. TUFLOW’s 2D engine produces detailed flood extent, depth, velocity, and hazard maps at whatever resolution the modeller specifies. For planning applications, this typically means 2-5 metre grid resolution, providing the detail needed to inform site layout and mitigation design.
• Linked 1D-2D capability. TUFLOW can be linked with 1D models (including its own 1D engine or external software such as Flood Modeller Pro or ESTRY) to create combined 1D channel / 2D floodplain models. This is the standard approach for detailed fluvial flood modelling in the UK.
• EA acceptance. TUFLOW is widely accepted by the Environment Agency and is the most commonly used 2D engine in EA-commissioned modelling. Using TUFLOW reduces the risk of technical objections from the EA regarding software choice.
• GPU acceleration. TUFLOW’s GPU-accelerated solver (TUFLOW HPC) can run models orders of magnitude faster than the CPU solver, making it practical to run high-resolution models over large areas and to test multiple scenarios.

Limitations

• Cost. TUFLOW is a commercial software package with significant licensing costs. This cost is justified for specialist flood risk consultancies but may be prohibitive for occasional users.
• Learning curve. TUFLOW does not have a graphical user interface (GUI) in the conventional sense. Model setup is primarily through text files and GIS layers, which gives experienced users great flexibility but presents a steep learning curve for newcomers.
• 1D capability. While TUFLOW has a 1D engine (ESTRY), it is less widely used for standalone 1D modelling than Flood Modeller Pro or HEC-RAS. Most practitioners use TUFLOW for the 2D component and link it with a separate 1D engine.

When to Use TUFLOW

• Surface water (direct rainfall) flood risk assessments.
• Detailed 2D floodplain mapping for planning applications.
• Linked 1D-2D fluvial models where the 2D floodplain component is critical.
• Flood map challenges requiring high-resolution flood extent mapping.
• Any project where EA acceptance of the 2D modelling approach is important.

HEC-RAS

Overview

HEC-RAS (Hydrologic Engineering Center — River Analysis System) is developed by the US Army Corps of Engineers and is freely available. Originally a 1D river modelling package, HEC-RAS has expanded significantly in recent versions to include 2D modelling, sediment transport, and water quality analysis.

Strengths

• Cost. HEC-RAS is free. This is a significant advantage for smaller consultancies, local authorities, and academic users. There are no licensing fees, no dongles, and no restrictions on the number of installations.
• 1D river modelling. HEC-RAS is excellent for 1D river modelling. It has a long track record, a mature and well-documented codebase, and a vast global user community. For straightforward fluvial flood risk assessments where a 1D model is sufficient, HEC-RAS is a strong choice.
• Graphical user interface. HEC-RAS has a comprehensive GUI that makes model setup, editing, and results viewing more accessible than TUFLOW’s text-file approach. This reduces the barrier to entry for less experienced modellers.
• Bridge and structure modelling. HEC-RAS has well-developed routines for modelling bridges, culverts, weirs, and other hydraulic structures in 1D. These are critical for river modelling where structures significantly affect water levels and flow distributions.
• EA acceptance for 1D modelling. The EA accepts HEC-RAS for 1D fluvial modelling and has used it in some of their own modelling programmes.

Limitations

• 2D capability. While HEC-RAS now includes a 2D solver, it is not as widely established or as rigorously tested in UK practice as TUFLOW. Some EA areas are cautious about accepting HEC-RAS 2D results, particularly for flood map challenges or high-consequence assessments.
• Direct rainfall modelling. HEC-RAS can apply rainfall to a 2D grid, but this capability is less developed and less widely used in UK practice than TUFLOW’s equivalent. For surface water flood risk assessments, TUFLOW remains the preferred tool.
• Performance. For very large or high-resolution 2D models, HEC-RAS can be slower than TUFLOW HPC’s GPU-accelerated solver. This can be a practical limitation for models that require many scenario runs.
• UK-specific features. HEC-RAS was developed for US practice, and some UK-specific requirements — such as EA blockage scenarios, specific climate change allowance application methods, and particular output formats — require workarounds.

When to Use HEC-RAS

• 1D fluvial flood risk assessments where a 2D floodplain is not required.
• Projects with limited budgets where software licensing costs are a constraint.
• Academic or research applications.
• International projects where HEC-RAS is the local standard.
• Preliminary modelling to scope the need for more detailed TUFLOW modelling.

Flood Modeller Pro

Overview

Flood Modeller Pro (formerly ISIS) is developed by Jacobs and has a long history in UK flood modelling. It is the EA’s legacy 1D modelling engine and remains widely used for river modelling, particularly in linked 1D-2D configurations where Flood Modeller Pro provides the 1D channel model and TUFLOW provides the 2D floodplain.

Strengths

• 1D river modelling pedigree. Flood Modeller Pro is the successor to ISIS, which was the EA’s standard 1D modelling platform for decades. It has an extensive library of hydraulic structures, flexible boundary conditions, and robust solver algorithms developed over many years of use in UK practice.
• EA legacy models. Many existing EA models were built in ISIS/Flood Modeller Pro. If you are working with or extending an existing EA model, using Flood Modeller Pro maintains compatibility and avoids the need to translate the model to a different platform.
• Linked 1D-2D modelling. The most common linked modelling configuration in UK practice is Flood Modeller Pro (1D) linked with TUFLOW (2D). This combination leverages the strengths of both packages — Flood Modeller Pro’s detailed channel modelling with TUFLOW’s high-resolution floodplain modelling.
• 2D capability. Flood Modeller Pro has its own 2D solver that can be used for floodplain modelling. While less widely used than TUFLOW for standalone 2D work, it is accepted by the EA and can be effective for straightforward applications.
• Steady-state analysis. Flood Modeller Pro supports steady-state (non-time-varying) analysis, which is useful for rapid screening, bridge capacity assessments, and situations where a full unsteady simulation is not required.

Limitations

• Cost. Flood Modeller Pro is a commercial software package with licensing costs comparable to TUFLOW. For firms that also use TUFLOW, maintaining licences for both packages is a significant overhead.
• 2D solver performance. Flood Modeller Pro’s 2D solver is generally slower than TUFLOW HPC for large or complex models. For high-resolution 2D modelling over large areas, TUFLOW’s GPU acceleration provides a significant performance advantage.
• Market trend. The UK flood modelling market has shifted towards TUFLOW for 2D work, and new projects are increasingly built in TUFLOW rather than Flood Modeller Pro’s 2D engine. This means there is a growing body of TUFLOW expertise in the market and a gradually shrinking pool of Flood Modeller Pro 2D specialists.
• Direct rainfall modelling. While Flood Modeller Pro can model direct rainfall, TUFLOW is the more established and widely used tool for this application in UK practice.

When to Use Flood Modeller Pro

• Working with or extending existing EA 1D models built in ISIS/Flood Modeller Pro.
• 1D channel modelling as part of a linked 1D-2D configuration with TUFLOW.
• Projects where the EA or client specifically requires Flood Modeller Pro.
• Steady-state analysis for bridge or culvert capacity assessments.
• Organisations that have invested in Flood Modeller Pro expertise and licensing.

How to Choose

The choice of modelling software should be driven by the project requirements, not by which package the modeller happens to prefer. Here is a practical decision framework:

What Type of Modelling Is Needed?

• Surface water / direct rainfall only: TUFLOW.
• 1D fluvial only: HEC-RAS or Flood Modeller Pro, depending on budget and whether existing EA models are available.
• Linked 1D-2D fluvial: Flood Modeller Pro (1D) + TUFLOW (2D) is the standard configuration.
• 2D fluvial floodplain only: TUFLOW.

Is There an Existing EA Model?

• Yes, in ISIS/Flood Modeller Pro: Use Flood Modeller Pro for the 1D component. Link with TUFLOW for 2D if needed.
• Yes, in HEC-RAS: Use HEC-RAS for the 1D component. Consider linking with TUFLOW for 2D.
• No existing model: Choose based on the modelling type required and EA preferences for the area.

What Does the EA Expect?

• Always check with the EA before committing to a modelling approach. Some EA areas have strong preferences for particular software, and using a package the EA is not familiar with can delay the review process.

What Is the Budget?

• If licensing costs are a constraint, HEC-RAS provides excellent 1D modelling capability at zero software cost. For 2D work, the cost of TUFLOW licensing is typically modest relative to the overall project cost and is justified by the time savings and EA acceptance.

Our Approach

At Aegaea, we use all three packages and select the most appropriate tool for each project. For surface water assessments, we use TUFLOW. For 1D river modelling, we use Flood Modeller Pro or HEC-RAS depending on the availability of existing EA models. For linked 1D-2D work, we use the Flood Modeller Pro + TUFLOW combination that is the UK industry standard.

We choose the tool that will deliver the best result for the project, not the tool that is most convenient for us. If you need flood modelling for your development, get in touch and we will recommend the right approach for your site.