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Flood visualisation and the importance of weather event modelling. Sun Yan Evans

Flooding incidents due to climate change are hitting the nation’s asset base with increasing frequency and severity. Digital technology has a key part to play in building resilience.

In December 2013, the east coast experienced severe tidal surge events. Defences were breached and overtopped, leading to coastal flooding. With defences weak and damaged, emergency services stretched and even more high tides forecasted for early and late January 2014, the Environment Agency needed to know where to deploy its resources most effectively.

There was no tool capable of quickly providing that kind of insight, but we were able to use our Water and Wave Overtopping Tool (WWOT) to rapidly calculate the water and wave overtopping rates for a long stretch of coastline for a number of tide and surge scenarios. The results were fed into a purpose-built flood inundation model to predict flood progression, identifying coastal areas at high risk of flooding as a result of storm surges. WWOT is now being used as a key support tool for flood prevention strategies and to inform the development of coastal infrastructure.

Combining multiple data sources

The Environment Agency already had a modelling system which incorporates forecast data on sea levels, wind speed and direction.

This does not take into account the type and condition of sea defences or the way storm surges impact on them. Beaches, dunes, sea walls, marshes, rock revetments and embankments are affected in different ways after events such as the December 2013 tidal surge. WWOT combines data on coastal defences with weather and tide information to create a detailed real time model of flood risk.

The data sources used in our visualisations include:

Weather forecasts: Weather data, such as wind speed and wind direction, is provided by the Met Office and fed directly into WWOT to predict wave height and overtopping rates for sea defences.

GIS modelling: We created a GIS model capturing information on the entire flood plain potentially affected by coastal surges, taking into account rural and urban areas, flood defences, topography and critical infrastructure to visualise the movement and spread of water on land. This incorporated:

  • LiDAR data: In the event of coastal surges, the flow of water on land is affected not only by the type of land but also by the changing elevations of the landscape and the presence of obstacles such as embankments, buildings and roads. Using LiDAR data, we were able to create an accurate model incorporating the changing elevations of coastal areas.
  • Aerial photography: Once we had created a model of the flood plain, we overlaid it with aerial photography. This made the visualisations more intuitive to users as it brought recognisable colours and shapes to the model, making it easier to recognise landmarks and to understand where the effects of coastal surges would be the most destructive.
  • Ordnance Survey data: Aerial photography was supplemented by Ordnance Survey data to highlight the main roads in the flood plain. Although these would have been clear from aerial photographs, highlighting roads separately allowed us to isolate the effects of flooding on the transport network.

Making use of flood visualisations

Our models were produced as interactive flood plain maps, 2D animations and 3D animations. Together, they enable users to:

Understand the effects of coastal flooding: Our models allow different flooding scenarios to be visualised, taking into account how the flow and spread of water would differ according to the level of wave overtopping and the conditions of the landscape and existing infrastructure.

Forecast flooding events: By modelling Met Office data for forthcoming storms, authorities can predict the severity and extent of flooding events and decide whether to issue flood alerts.

Devise flood prevention strategies: Interactive modelling allows users to devise flood prevention strategies and to model how different flood defence schemes would withstand flooding events, thereby allowing optimisation of defence strategies.

Adapt evacuation and relief strategies: By understanding which areas will be most affected by coastal surges, local authorities can determine which areas should be evacuated at times of extreme tidal surge events. Also, by isolating the roads in our models, users can visualise the impact of flooding on the road network and plan routes for relief vehicles accordingly.

Plan investments in infrastructure: Local authorities can use the visualisations to help plan investments in infrastructure, ensuring that new assets are able to withstand the effects of projected flooding events and that they don’t exacerbate the effects of flooding on adjacent assets.

Taking the project further

The modelling and 3D Flood Visualisation Tools cannot only be used to predict and visualise the flood risk for coastal areas, but they could be expanded to take in other areas and uses:

Development for inland flooding: Flooding due to overtopping of river defences could be modelled using a similar system, incorporating Met Office data on rainfall. This would be useful for areas which are frequently at risk of river flooding.

Improve food security: Our modelling and 3D visualisation tools can be used to see the effect that flooding would have on agricultural areas to reduce risk to food security, especially in countries which depend on agriculture for exports.

Safeguard the transport, power and water networks: Flooding to critical infrastructure could lead to cascade system failures, as other interdependent assets are adversely affected or unable to function. Applying our modelling techniques on a regional or national level together with data on infrastructure use will highlight where flooding events will have the biggest impact, allowing for targeted flood defence work or the design of alternative routes and rapid recovery plans, minimising economic losses.

Climate change impacts cause an estimated US$100B a year in global losses, a value set to increase rapidly as climate change worsens and the asset base grows. Flooding events are a risk globally.

Detailed visualisation projects will be key to mitigating impacts, allowing asset owners and emergency planners to model the effects on the built and natural environments and allowing preventive strategies to be optimised and implemented.

This article was first published by Infrastructure Intelligence.

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