Flood Forecasting and Early Warning: An Example from the UK Environment Agency - Reducing Disaster: Early Warning Systems for Climate Change - page 180

10.3.1 Flood Map

In England, the Environment Agency has produced a 'fl ood map' to try and answer
these questions. Using varying methods depending on their geographical availability
ranging from 'simple' GIS analysis up to 'complicated' 2D models, the Environment
Agency has mapped the risk of fl ooding for a 1 in 100 (or greater chance), 1 in 200
(for coastal fl ooding) and 1 in 1,000 (or greater chance) of fl ooding from river or sea.
These maps are available for everyone to view on the Environment Agency's web-
site (EA 2013d ). They include no defenses. In other words, they present a 'worst-
case' scenario to plan and build better adaptive capacity and coping mechanisms.
The Environment Agency has also produced;

• A fl ood map that includes the presence of defences. The National Flood Risk

Assessment (NAFRA) provides the likelihood of fl ooding at a national scale
with cells of 100 m by 100 m (EA 2013b ). The results are presented into three
categories as used by insurance industry. For example:

- Low - the chance of fl ooding each is 0.5 % (1 in 200) or less.

- Moderate - the chance of fl ooding in any year is 1.3 % (1 in 75) or less but

greater than 0.5 % (1 in 200).

- Signifi cant - the chance of fl ooding in any year is greater than 1.3 % (1 in 75)

(EA 2013b ) .

• A fl ood map for the risk of surface water (fl ooding from heavy rain and exceed-

ance of drainage capacity. Banded in two categories (deep/less deep) for two
scenarios (1 in 30 chance, 1 in 200 chance) (EA 2013e ).

• A fl ood map for the risk of reservoir fl ooding (for large reservoirs holding over

25,000 cubic metres of water) (EA 2013d ).

All of these are, or soon will be, available for free from the Environment Agency's
website.

10.4 Mitigating Flooding

Once risk areas are identifi ed, actions can be taken to reduce the risk. Mitigating
fl ooding is not an easy, small or straightforward task. There are many different
approaches favoured in different locations around the world, ranging from the mini-
mum approaches, such as, a simple GIS-based mapping for fl ood risk and introduc-
ing ecosystem-based preventive measures (Defra 2007 ) to engineering defences
which protect all but the most extreme events (Deltares 2010 ).
This range can also be observed within countries. In England, for example, the
Environment Agency uses at least four methods to reduce fl ood risk:

1 . I in fl uencing the planning process to avoid inappropriate development in fl ood
risk areas, for example, Flood Risk Assessments (EA 2013f ).