We understand that understanding flood terminology can be confusing; we often receive questions surrounding the data and general terms on our flood reports.

The detail below covers the types of data we interpret, common misconceptions and how we analyse the level of flood risk to a property



Jill Boulton, Director, JBA Risk Management

What is Flood Re?

Flood Re is a co-operation between the insurance industry and the government to find a solution to make insurance both available and affordable for people who live in flood risk areas. Moving forward, flood payments for insurance will be dependent on your council tax band – for example council tax bands (A) and (B) are approximately £210 whereas band (G) is approximately £540.

Flood Re is scheduled to go live in April 2016 and should enable people who struggle to get flood insurance to obtain it moving forward. Having this insurance protection won’t take away the horror of being flooded, it won’t stop you having to leave your home or having your possessions damaged so it is important to think carefully before purchasing a property that has a flood risk.

How does JBA measure flood risk?

JBA assess flood risk by looking at both the extent and depth of flooding using both volume and height mapping available.  Height mapping is typically accurate between 15cm and 1m. A volume of water is put over the mapping which is effectively like pouring water over a landscape and it is this that provides the extent and depth of flooding.

JBA models at 5m x 5m – which compares with a 50m x 50m model that is typically available as free data. When flooding is modelled at 5m x 5m there will be more than one hit on a building, meaning flood risk is fully documented and all potential flood risks are identified.  If looking at the 50m x 50m data it’s unlikely that the full extent of the flood risk will be known.

Flooding is complicated, there are various types of flooding which are assessed differently – for surface water – rainfall is measured in either a one hour or ten hour period. The rainfall is applied to the height map and the movement is reviewed as are the depths over the length of the run. With river flooding the volume of water in the river is assessed and then placed over the height map which provides the extent and depth of flooding. Coastal flooding is more complicated as the bathymetry needs to be reviewed to assess how the water will move, combine that with wind speeds and pressure, this is then projected in-land to work out where the flooding will occur.

Why is it important to measure flood risk?

One of the most difficult things for people looking to purchase a property is to understand the potential risk of flooding. It is a terrible experience which can cause significant damage both physically and emotionally. Solicitors have a vital role in letting their clients know about the possibility of flooding to ensure the potential purchasers have a full view of the risks ahead of the transaction.

Climate change is already affecting our weather patterns; we are seeing far more winter showers – where previously you might have 2” of rain in a month, this amount can now fall within an hour. This increase in water volume puts pressure on the drains which is resulting is more surface water flooding events.


Understanding flood risk

Different types of flood risk

Probability of flooding

What’s included in our reports?