Flood Modelling Software: Tools & Techniques Guide

Flood modelling software predicts how water will behave across a landscape: where it will go, how deep it will get, and how fast it will move. Engineers, planners and flood risk consultants use it to assess risk, test mitigation and support planning applications, due diligence and property transactions. This guide sets out how the software works, the main packages used in the UK, how to choose between them, and what’s changed in 2026.

The Environment Agency’s river modelling technical standards expect every hydraulic model to be accompanied by a Model User Report — worth planning for before modelling starts, not once the model is already built.

The history of flood modelling software

Early flood risk work relied on manual calculations and historical records, which gave only a rough sense of likely flood behaviour. Digital modelling began in the 1960s and 1970s, when the first computer-based tools used simplified equations to simulate water flow along a channel.

By the 1980s and 1990s, one-dimensional (1D) tools such as HEC-RAS, developed by the US Army Corps of Engineers, had become standard for river flood studies. As computing power grew, two-dimensional (2D) models followed, adding the ability to simulate flooding spreading across land rather than staying confined to a channel.

The 2000s and 2010s brought integrated 1D/2D modelling and better real-time data, partly in response to the need to plan for climate change. Cloud computing and Geographic Information Systems (GIS) integration have since made models faster to build and easier to update. 2026 has added two more developments worth knowing about: the first public beta of a rebuilt HEC-RAS, and a small but growing set of AI-assisted forecasting tools, both covered below.

Understanding 1D and 2D flood modelling

1D flood modelling

1D models treat a river or drainage channel as a single line, calculating water level and flow along its length. They’re quick to build and run, and remain a good fit for straightforward river studies, such as assessing a bridge or culvert. What they can’t do is show how water spreads once it leaves the channel and crosses a floodplain.

2D flood modelling

2D models simulate flow across a surface using a grid or mesh, so water can move in any direction. This makes them the better tool for mapping urban flooding and floodplain extents in detail, though they need more computing power and better terrain data than a 1D model.

1D/2D integrated modelling

Most real flood events involve both a channel and the surrounding land, so many projects now pair a 1D river network with a 2D floodplain mesh. This is especially useful in urban areas, where a piped drainage network interacts directly with surface water flooding, and it’s now the default starting point for most detailed UK flood risk assessments.

How to choose the right flood modelling software

There’s no single best flood modelling software. The right choice depends on the site, the question being asked, and who needs to accept the result — worked through in roughly this order.

1. Start with the flood sources, not the software. A simple river-only study in open countryside may only need a 1D model; a site where river, surface water and drainage networks interact will usually need an integrated 1D/2D approach.
2. Check the data you actually have. 2D and integrated models need good terrain data, typically LiDAR, plus reliable inflow or rainfall data. Without it, a more sophisticated model won’t produce a more reliable answer, only a more convincing-looking one.
3. Weigh cost against complexity. HEC-RAS is free and widely used for river-only studies; TUFLOW, Flood Modeller, InfoWorks ICM and MIKE+ are commercial packages licensed by module, which matters on smaller or more straightforward projects.
4. Build in EA and LLFA acceptance from the outset. The Environment Agency’s river modelling technical standards call for a Model User Report alongside any hydraulic model submitted as evidence, so a reviewer can understand and rely on it.
5. Decide who builds it. Straightforward 1D studies can often be built and interpreted in-house by an experienced consultant; complex integrated catchment models, or anything likely to be challenged by a regulator, usually justify a specialist modeller’s time.

Flood modelling software used in the UK

Six packages account for most flood modelling carried out on UK projects today, from free river-only tools to commercial integrated catchment platforms.

InfoWorks ICM was originally developed by Innovyze; Autodesk has developed and licensed it since acquiring the company in 2021.

1D tools such as HEC-RAS are fast for simple river studies. 2D and integrated 1D/2D packages such as TUFLOW, InfoWorks ICM and MIKE+ need more data and computing power, but handle complex, urban or multi-source flood risk far better. The right choice comes down to project scale, available data, and how much detail the site genuinely needs.

Flood modelling in planning and property decisions

Flood risk assessments for planning applications

In England, a Flood Risk Assessment is normally required for development in Flood Zones 2 and 3 under the National Planning Policy Framework. Where national mapping isn’t detailed enough for the site, flood modelling provides the flood levels, extents and mitigation evidence, including Sustainable Drainage Systems, that planning authorities, the Environment Agency and Lead Local Flood Authorities expect to see.

Due diligence, property transactions and homebuyer assessments

Developers, investors and mortgage lenders rely on flood modelling to understand fluvial, surface water and groundwater risk before committing to a site or a purchase. For homebuyers, a modelled assessment can give a clearer answer than national screening data alone, particularly where a lender or insurer has raised a specific concern.

What’s new in flood modelling for 2026

A few things have moved on since this guide was first written.

NaFRA2, the Environment Agency’s updated national flood risk assessment, is on track for full national coverage by summer 2026.

• HEC-RAS 2025. Entered public beta in 2026 as a ground-up rewrite, though USACE doesn’t yet recommend it for production studies — HEC-RAS 6.6 remains the version most UK consultants rely on today.
• Updated EA standards. The Environment Agency’s river modelling technical standards were most recently updated in May 2026, and continue to expect a Model User Report alongside any hydraulic model submitted as evidence. Our guide to the standards covers what this means in practice for a Flood Risk Assessment.
• NaFRA2. Feeding better river, surface water and climate change data into the Flood Map for Planning as coverage completes.
• AI and machine learning. Starting to support flood forecasting rather than replace modelling outright — Northumberland County Council’s Defra-funded FloodAI pilot and Jacobs’ Flood IQ platform both use machine learning alongside real-time data to flag flash-flood risk faster. Our separate look at AI in flood risk management covers what these tools can and can’t do today.

The future of flood modelling

Climate change is increasing the frequency and severity of flooding, and flood modelling software is adapting: faster solvers, better terrain data, and an early but growing role for AI-assisted forecasting alongside traditional hydraulic modelling. None of that changes the basic question a developer, homebuyer or investor still needs answered: which software, and which technique, actually fits the site.

At Unda, we build 1D, 2D and integrated flood models in-house as part of our flood risk assessments, due diligence work and homebuyer reports. If you need help navigating planning requirements or assessing a site’s flood resilience, our team is here to help.

Frequently asked questions