The Environment Agency has developed a nationally consistent set of standards for coastal flood modelling. Two numerical modellers at ABPmer review them.

Coastal flood models are sophisticated decision-support tools. They can inform risk management decisions, emergency response actions, and provide evidence to restrict development in areas vulnerable to flooding.

To improve the understanding of what is appropriate model quality and maintenance, the Environment Agency has developed a nationally consistent set of standards for coastal flood modelling. 

Our in-house Modelling Team regularly develops models of estuarine, coastal and offshore systems to support feasibility and design studies, as well as impact assessments and operational planning. Here Jonathan Griffiths (Modelling Consultant) and Adam Fulford (Senior Modelling Consultant) discuss the new modelling standards and their application.

JG: The new modelling guidelines from the Environment Agency are designed to help regulators assess the suitability of a model but they also look like a great checklist for us to use while building our numerical models. There’s all sorts in the guidelines from the quality of source data we should use to drive our models such as tide and surge conditions, the pathways such as bathymetry and LiDAR data and the actual model build such as the resolution and calibration. The guidelines look good but I’m a bit concerned as the model we’ve been building looks like it will only score a grade B instead of A.

AF: That’s OK, the grading system is used to determine the suitability of a model against a specific purpose. In our case, we are looking at which managed re-alignment option is best so we are building an Appraisal standard model which is classified as grade B. Once appraisal has been completed, the project might move to the Design stage where it’s likely we will model a detailed scheme design. It’s important to build a model that’s suitable for the problem we’re trying to solve.

JG: I guess that means it’s a good thing that we’ve mainly focused on correctly predicting water levels.

AF: Yes, as it’s a managed re-alignment project which will have implications for flood risk it’s very important we correctly predict water levels.

JG: Our modelled water levels fit very well with the measurements our survey team have recently taken and I’m confident that our model is suitable for the problem we are trying to solve. It meets most of the Appraisal criteria, however in one section of the model we’ve used bathymetry data that’s more than 10 years old. I’m really struggling to source a more up-to-date dataset – will we need to carry out a bathymetric survey?

AF: Not necessarily, this document should only be used for guidance as there are often cases where it will not be applicable. In this case we have a well calibrated model which indicates that the bathymetry in that area is not influencing the hydrodynamic characteristics of the main area of interest. Also, the baseline physical processes characterisation reveals that that part of the seabed isn’t very dynamic. That may even be why you’re struggling to find recent bathymetric data covering the area, since there isn’t a real need for frequent, repeat surveys. If you can provide sufficient evidence, a well-informed assessor will understand that falling outside of this guideline will not reduce the quality of the model and will not make it any less fit-for-purpose so the scoring shouldn’t be affected. It’s important that you have regular clear communication with the client and, where possible, the model assessor to avoid any misunderstandings when it comes to the guidelines.

JG: Thanks Adam, if used properly these guidelines seem like a helpful tool that we can use alongside our own internal modelling standards. For my next project, I’ll be modelling thermal plumes, are these guidelines appropriate for this type of project?

AF: You could use them to guide you for that project but be aware that they are mainly applicable to flood risk so it’s important to remember the focus of the study and not get distracted by guidelines that aren’t relevant for your project.

Prepared by Jonathan Griffiths and Adam Fulford