Bristol Flood Risk Assessment

Challenge

Our Specialist Flood Risk Services (SFRS), developed with Future Climate Info (FCI), help homebuyers and commercial property purchasers gain a greater understanding of the risk of flooding to a property.

In this example, an FCI report for a semi-detached house in Bristol recommended further actions with respect to river and surface water flooding. A Report Review, the initial specialist flood risk service, was commissioned to explore this further.

Solution

The house threshold is raised four brick courses and so was estimated to be only 0.3m above the surrounding ground.

The FCI report had identified a nearby watercourse which flows in culvert. Should that culvert capacity be exceeded there will be a flood risk on the road because of overland towards the downstream reach of the watercourse.

The Environment Agency’s ‘Flood map for planning’ shows that the house is in Flood Zone 3. This means the annual probability of flooding is greater than 1 in 100-years. Their ‘Flood risk from surface water map’ shows there is also a high risk of surface water flooding to the house.

The Environment Agency map agrees with JBA’s surface water flood map. High risk means that the chance of flooding is greater than 1 in 30-years. Both maps show that the depth of flooding on the road would be greater than 0.3m.

Ground levels based on aerial data show that there is a 150m long dip in levels along the road where surface water could pond. Depths of flooding up to 0.4m could arise. Given the house only appears to be raised 0.3m above the surrounding ground, shallow internal flooding due to surface water cannot be discounted.

Benefit

The Report Review confirmed that the house was at risk of flooding from both river and surface water. Given the shallow nature of the flood risk, the use of flood barriers and air brick covers at the house would prevent flood water entering the house.

Want to know more?

For more information on this project contact Mark Bentley. You can also find out more on the Specialist Flood Risk Services website or in our previous Specialist Flood Risk Services project overview.



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