What is flood modelling?
Flood modelling (or hydraulic modelling) is the process of computing a set of complex equations, to simulate flood patterns and predict flood data, including flood levels, flows and velocities.
The accuracy of flood modelling is dictated by numerical equations adopted, as well as by the quality of input data (topography, hydrology and representation of physical features).
A flood model can help you establish one or more of the following:
- Flood maps for different flood events (including a range of return periods)
- A full understanding of the local flood mechanism
- Flood difference maps to illustrate the difference between pre and post-development scenarios
- Integration of 1D features in the model, including bridges, culverts, flood defences and others.
Our models can be used to challenge national-scale models, as well as to inform the need for the sequential test, following the application of mitigation measures.
Our models are primarily undertaken in the Environment Agency’s ESTRY-TUFLOW software, which can be used to produce 1D, 2D and coupled 1D-2D models, depending on the type of conditions to be computed.
“JOFLOWS can help you, whether you are a homeowner, architect or developer bringing life to a property”
— João Gil, Founder of JOFLOWS
When is flood modelling required?
Locations at significant flood risk do often require flood modelling, particularly if one or more of the following applies:
- There is no modelling data for a certain watercourse
- The national-scale model outputs are deemed inaccurate or unreliable
- The latest climate change allowances have not been included in the national-scale model
- Topography, hydrology or other input data is no longer deemed fit for purpose
Our flood models integra pluvial sources, fluvial sources or a combination of both. Joflows specialises in integrated catchment modelling, fluvial flooding, hydrology, and flood risk assessment, offering expert guidance across the UK and internationally.
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What is required to build a flood model?
The information required to build a flood model depends on whether a flood model already exists or not, and how accurate this is.
As part of our work, we undertake reviews of existing models to establish if improvement are required and to assess the assumptions and limitations underlying each model.
If no hydraulic model is available to inform the assessment, the following elements are typically required:
- Hydrology assessment, unsing the latest software and tools (ReFH2, FEH-statistical, observed data)
- A bed survey of the watercourse, including full cross-sections at key locations (bridges, embankments etc.)
- A topographic survey of the floodplain, including culverts.
We have a network of partners and we can help you finding a suitable qualified provider.
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FAQs
The EA’s flood maps show my site to be at risk of flooding, but it has never been flooded. What should I do?
The EA’s flood maps comprise a set of high-magnitude flood events, with return periods of 30 to 1,000 years. However, these maps are derived from a national-scale approach, which might not be suitable for a site specific flood risk assessment. This means that inconsistencies are possible, which can result in inaccurate conclusions.
To find out whether your development would benefit from hydraulic model, reach out to one of our experts.
Do I always need a bed survey of the watercourse? What does it involve?
The answer to this question depends on various factors. If the model aims to model a fluvial flood mechanism, then a survey of the watercourse bed is required, unless we can obtain a model from the Environment Agency and this is deemed to be fit for purpose.
A bed survey involves capturing elevation data, including cross-section profiles of the main channel(s) and key hydraulic features, including bridges and culverts. As part of this element of work, a team of external suitably-qualified surveyors will visit the site to record the information.
What is the meaning of 1D and 2D modelling?
As the name suggests, 1D modelling involves the representation of a hydraulic feature as a 1D element, where the velocity pattern might follow a single direction. An example of this would be a river, when flows are kept within the main channel, without spilling onto the floodplain.
For higher magnitude flood events, flows tend to go off-bank onto the floodplain. Under these circumstances, it is important to represent the flood mechanism around buildings and topographic features. This also means velocity vectors can no longer be assumed to have a single direction. Often, 1D models are linked to 2D models as the representation of a river channel as a 2D domain would often trigger high computation times.
An example of a 2D model are pluvial-triggered flood events in urban areas, where 1D features are limited and the channel storage provided in small watercourses is not considered a limiting factor.
