Flood Zones for Local Planning Authorities in England – Your Questions Answered
Flood Zones – Your Questions Answered
1
Introducing Flood Zones
Q:
I’m not sure what Flood Zones are all about – what are they?
A
Flood Zones are the way that Government Planning Policy Guidance 25 on Development
and Flood Risk (PPG25) states that planners should look at the relative risk of flooding in
different areas. PPG 25 identifies three different risk zones from Zone 1 (lowest probability
of flooding) to Zone 3 (highest probability of flooding). There is a more detailed explanation
in the accompanying Briefing Note, but an important point is that PPG 25 says that Flood
Zones should show where flood waters would go if there were no flood defences.
2
How Flood Zones Affect LPAs
Q:
Do I need to know about Flood Zones?
A:
Yes, Flood Zones are central to the application of PPG25. Table 1 note (a) and paragraphs
30 & 31 of PPG25 explain the sequential test that must be carried out for all development
proposals using Flood Zones.
Q:
I’ve already got the Agency’s Indicative Floodplain Map (IFM) – do I need to use Flood
Zones?
A:
Yes, Flood Zones replace the IFM from 1 July 2004. The Agency will use Flood Zones, in
accordance with PPG25, in responding to planning applications from 1 July 2004.
Q:
How do Flood Zones differ from the IFM?
A:
The IFM comprised information from a number of difference sources; from flood events of
differing severity and from some basic modelling – it could tell you that there was a risk of
flooding but not how often and not very reliably. Flood Zones are based on the latest
modelling techniques and data of known quality. There are some places where our local
Area Strategic Planning teams know, from experience, that the Flood Zones do not seem
quite right, but we don’t yet have any better data to supplement this. However, Flood Zones
do give a much better indication of the frequency of flooding, and more accurate extents for
extreme flood events.
3
Using Flood Zones
Q:
I’ve looked at the CDs, and read the briefing note, but I still have a few questions.
A:
You will be contacted by someone from your local Area Planning Liaison team during July
2004 to arrange support for you to use Flood Zones. They will also explain to you how our
new Standing Advice on Development and Flood Risk will relate to Flood Zones.
Q:
What should I do if the river doesn’t fall inside the floodplain, and I need to consider a
planning application nearby?
A:
Flood Zones show the route that floodwater from the river would take when finding the lowest
path through the floodplain. Sometimes the river channel has been engineered and moved
away from its natural course over the years, but the floodplain shown by Flood Zones, in the
lowest part of the valley, really is in the right place. In other cases, although Flood Zones
provide wider and more consistent coverage than the IFM, our data will never be perfect.
The briefing note on your June 2004 Flood Zones Data CD explains why there are some
misalignments. If you contact your local Area contact, they will be able to provide you with
more information on their confidence in the data at any specific location, and will be able to
recommend an appropriate approach.
Issued by Flood Mapping Programme, Environment Agency, Rio House, Bristol
V1 18 June 2004
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Flood Zones for Local Planning Authorities in England – Your Questions Answered
Q:
Why are you showing this area as at risk of flooding, when we know the river channel
can accommodate high flows?
A:
Flood Zones show the extent of flooding without flood defences, including locations where
the channel capacity has been increased so that the river can carry more water, as Flood
Zones assume that only the natural capacity of the channel is available to carry flood flows.
The Flood Risk Assessment (FRA) accompanying planning applications should reflect
issues such as whether flood defences are present, their condition (for example, are they
maintained regularly, or have they been abandoned?), whether the channel capacity has
been increased, and the effect of blockages and obstructions, which can result in more
widespread flooding.
Q:
I’m assessing a planning application beside the river. The IFM showed this site in the
floodplain, but it isn’t included in Flood Zone 3.
A:
The IFM comprised information from a number of difference sources: from flood events of
differing severity and from a range of other studies. It included historic flooding, even from
major events with less than a 1% chance of occurrence in any one year. If the site you are
considering falls within an area that was in the IFM because it has flooded in one of these
major historic events, it would now fall within Flood Zone 2. In other places, it may be that
the national modelling included in Flood Zones has provided better information on the
extents of flooding. Standing Advice will guide you on how to assess the application.
Q:
Why don’t Flood Zones show the benefit of flood defences?
A:
PPG25 specifically states that Flood Zones should ignore the presence of flood defences.
However the presence and condition of flood defences should be taken into account as part
of the Flood Risk Assessment accompanying a planning application. Your local Agency
contact will be able to provide advice on flood defences in the area.
Q:
Do Flood Zones take account of future climate change?
A:
No, Flood Zones show the picture at 2004. The Agency will be developing Flood Zones for
the year 2050 over the next year or so. It is, of course, important that the future risk of
flooding arising from climate change is taken into account, and at present this should be part
of the Flood Risk Assessment accompanying a planning application.
Q:
Why are there some places where Zone 3 runs straight into Zone 1?
A:
This is due to the natural topography of the floodplain. In a steep-sided valley, or where
there are coastal cliffs, it is possible for different depths of water to result in very similar
floodplain extents. Thus the flood extent in a flood with a 0.1% chance per year will be
deeper than a flood with a 1% or 0.5% chance in any one year, but the extent of flooding
may be the same, giving the appearance that there is no Zone 2 in this location.
Q:
Why is there an abrupt change in the floodplain in a few locations?
A:
This is where two datasets from different sources have been joined together, for example,
where the national modelling is joined to mapping from a more detailed study. We have not
smoothed the transition on the Flood Zones, as this would have been misleading. These
abrupt changes will help us to identify locations where further studies may be required.
Issued by Flood Mapping Programme, Environment Agency, Rio House, Bristol
V1 18 June 2004
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Flood Zones for Local Planning Authorities in England – Your Questions Answered
4
Flood Zones, Flood Risk Standing Advice and Strategic Flood Risk
Assessments (SFRAs)
Q:
We carried out a modelling exercise to produce a SFRA with input from the Agency,
and produced flood risk maps from this. Now that we have Flood Zones, does this
affect how we use the SFRA outputs?
A:
No. Flood Zones show the extent of flooding without flood defences. SFRAs, which look at
flooding in detail in your area, including the effects of flood defences, serve a different
purpose. Both are valuable for planning purposes. SFRAs will be an important component
of individual Flood Risk Assessments accompanying planning applications. Furthermore,
some SFRAs and FRAs may provide information (in the form of maps which do not show the
effects of flood defences) that helps us to improve our Flood Zones.
Q:
How do Flood Zones fit with the Standing Advice for the IFM, which my local Agency
contact explained to me recently?
A:
We have revised Standing Advice to go with the Flood Zones, and the IFM version is now
superseded. The limited scale changes involved in this update should allow Local Planning
Authorities to switch to the Flood Zones version without further reference to the Agency. We
will explain the changes on the web site www.pipernetworking.com. If you have not used
Standing Advice before or if it has been delivered to your Authority but you still have
questions or concerns about how to implement it, we suggest you get in touch with your local
Planning Liaison team. Someone from this team will in any case be contacting you during
July to help you with any queries and will visit you if necessary.
Q:
I have already agreed Standing Advice relevant to my LPA, with my local Environment
Agency Area contact. Does this new data mean that it is invalid?
A:
No, your local Environment Agency Planning Liaison contact will be in touch with you to
explain how to use your locally agreed Standing Advice with the Flood Zones.
5
Future of IFM, Flood Zones and other mapping products
Q:
What will happen to the IFM on the Internet?
A:
In October, we will replace the IFM when we launch our new Flood Map on the Internet. This
will provide much more information on flood risk. The Flood Map will show Flood Zones, and
the probability of flooding. Gradually we will also add information on flood defences and the
areas that benefit from flood defences. Only the Flood Zones layer should be used in
applying Standing Advice.
Q:
How will this data be updated, and how often?
A:
The data will be updated every three months as part of our updates to the Flood Map on the
Internet, as we add to our understanding of flood risk. The first update will take place in
October, when we launch our new Flood Map on the Internet. We will send you the updated
Flood Zones, together with information on flood defences and areas that benefit from flood
defences, on CD. If we have not updated the information in your area in any three-month
period, we will write to inform you of this.
Issued by Flood Mapping Programme, Environment Agency, Rio House, Bristol
V1 18 June 2004
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