Introduction

In 2016 SEPA released revised indicative maps showing areas at risk from river, coastal and surface water flooding throughout Scotland. The mapping was undertaken to improve the understanding of flood risk, to raise public awareness of flood risk, and encourage individuals and organisations to take steps to reduce the risk to themselves and their property, where appropriate. This study has provided updated flood maps for Ballater. This updated mapping provides a better level of detail, sufficient to assist local authorities to take a more proactive approach to flood risk management, and develop avoidance, alleviation and assistance strategies through exercise of their land use planning, flood protection and emergency planning functions. These maps are located at http://map.sepa.org.uk/floodmap/map.htm.

What do these maps show?

When a river floods the severity of the flood is known as a 1 in x year flood. This terminology represents the probability of that event occurring in any year. For reference, the December 2015 event (Storm Frank) on the River Dee in Ballater is estimated to have had almost a 1 in 200 chance of occurring in any year (or 0.5% annual probability). This does not mean that the flood will occur once every 200 years; it could occur tomorrow and again next week, but on average a flood of that severity will occur once every 200 years. For example, there is a 1 in 100 (or 1%) chance of a flood exceeding the 100 year flood in any one year. A list of frequently used return periods and their respective annual probabilities is provided in the table below:

Return Period	Annual Probability [AP] (%)
2 year	50
5 year	20
10 year	10
25 year	4
30 year	3.33
50 year	2
75 year	1.33
100 year	1
200 year	0.5
1000 year	0.1