Award-winning 2D hydraulic model

Fast, accurate representations of flow routing across flood plains

JFlow is a world-leading software package for simulating flood risks at anything from local to continental scales including river, surface water, coastal and dam break floods.

The first modelling package of its kind to make use of GPU technology, simulations are completed faster and more efficiently.

High performance modelling


  • Accounting for losses from rainfall hyetographs due to interception and other processes

  • Spatially-distributed and depth-varying Manning's n values

  • Ability to trigger the release of water from an inflow depending on water depth

  • Gutter and glass wall boundary conditions

  • Pre-defined and dynamic stopping criteria

  • The ability to implement a drainage rate grid  

  • Microsoft Access interface which allows queries to be run to automate model setup


  • Final and maximum depths and velocities

  • Hazard index options

  • Final water levels

  • Velocity components and directions (at maximum velocity and hazard)

  • Initial and maximum inundation times

  • Intermediate grid outputs (depth, velocity, water level, velocity components and hazard index) 

  • Monitor points and cross-section monitoring lines

  • Statistical outputs


JFlow has undergone rigorous testing during its development, both internally and externally. In 2012, JFlow took part in the benchmarking exercises set up by the Environment Agency and the University of Reading. In these tests, JFlow performed very well, with runtimes much faster than average and results that were consistent with the expected outputs.

Increasing the maximum size of JFlow simulations 

JFlow has recently been developed to make use of multiple graphics cards, allowing a single simulation to be executed on more than one device. This can help to either speed up model runs, or substantially increase the maximum grid size. 

This functionality, combined with another new feature called 'Indexed Grids', allows JFlow to model large catchments (or even small countries) in a single simulation at high resolution.  For example, the Severn or Thames catchments could be modelled on a 10m grid.  Ultimately, however, any limits on the scale of JFlow models are now entirely due to the hardware available.

These new features are enabling clients to do more with JFlow and to streamline existing models. For example: 

  • JBA Risk Management are using these features to produce a global rainfall inundation map. As whole catchments can be modelled in one go, the time required for setting up the model and post-processing the results has been substantially reduced.  In addition, the 'Indexed Grids' code has substantially reduced runtimes.

  • The multi-GPU code has been used by JBA Consulting for simulating flooding within the Sacramento Valley in California. It has enabled rapid assessments of complex catchment management options that incorporate levee realignments, additional bypass channels and changes to weir operations.

The Science Behind JFlow

JFlow solves the St Venant Shallow Water Equations using a Godunov finite volume numerical scheme.

Case Studies

Central Valley, CA

JFlow was used to simulate a series of design flood events for six different return periods, with the catchment split into a...

The Comprehensive Flood Map UK

The Comprehensive Flood Map UK covers flood hazards from river, coastal surface water, groundwater, dam break etc.

Updated Flood Map for Surface Water

JBA was commissioned by the EA and NRW to deliver a 2-metre resolution surface water flood map for England and Wales.

The Europe Flood Map

The Europe Flood Map (EFM), modelled using JFlow, provides consistent mapping across 13 European countries.

Award Winning Software

In 2012, JFlow was a bronze medal winner in the Royal Academy of Engineering MacRobert Awards, recognising the innovative nature of JFlow’s algorithms and the cutting edge use of GPU technology.

JFlow Timeline

Contact Us

For more information on JFlow please email jflow@jbaconsulting.com

Frequently Asked Questions

In 2012, the Environment Agency (in partnership with the University of Reading) organised a series of benchmarking tests for hydraulic models such as JFlow. A number of different software packages participated in these tests and the solutions provided by JFlow were consistently in agreement with the majority of other commercial models. Therefore, users of JFlow can have a high level of confidence in the numerical accuracy of the JFlow algorithms. To view the benchmarking report, click here.

There are a number of factors that will affect the speed of a JFlow simulation, including the size and resolution of your model, the percentage of the model domain which is wet and the graphics card available for use. However, a good indication of the speed of JFlow is that in the Environment Agency benchmarking tests of 2012 it was consistently quicker other Shallow Water Equation solvers. The speed of JFlow has been improved further since then.

As with model speed, the maximum grid size in JFlow will depend on the memory available (both RAM and GPU global memory) and the model setup. Using the multiple GPU version of JFlow on a typical computer from JBA's grid, you should be able to model domains with well in excess of 100 million cells. However, we are always looking at ways to save memory, such as with the new active grids feature (which in testing comfortably modelled the whole of Wales at 15m resolution).

Yes, JFlow is available to purchase. Please contact us to discuss your needs.

We are happy to undertake some test model simulations on your behalf to help you to determine whether JFlow is suitable for your needs. Please contact us at jflow@jbaconsulting.com and we will be happy to discuss this with you.

About JBA

We are engineers, environmental consultants, designers and scientists, committed to improving the natural and built environment and creating sustainable places to live and work.

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