1. A GIS-BASED APPROACH FOR FLOOD RISK MAPPING IN FINLAND
Working Group F
Thematic Workshop on Flood Mapping
Dublin, 17 – 19 September, 2008
A GIS-BASED APPROACH FOR FLOOD RISK MAPPING IN FINLAND
Mikko Huokuna and Mikko Sane
Finnish Environment Institute, SYKE
Petteri Alho, Jukka Käyhkö, Eliisa Lotsari and Laura Lehtiö
Department of Geography, University of Turku

2. Background Information Flood hazard maps in Finland
There have been flood maps available only for a couple of years in Finland
The development of flood mapping process started after the Working Group on Extreme Floods gave it recommendations in 2003
Flood mapping was listed as one of the key measures in flood risk management
The guidebook for flood hazard mapping was published 2006
Now there are flood hazard maps ready for about 60 locations and more locations are mapped every year

3. Background Information Flood hazard maps in Finland
The available national digital elevation models 10x10m (height accuracy a. 1m) or 25x25m (accuracy a. 1,8 m) are not accurate enough. In most cases local elevation information has been used in flood mapping.
The development of a new national DEM is going on
based on laser scanning; km2 was scanned 2008
final product DEM 2x2m (accuracy <0.3 m)
Ready for the whole country 2020; flood prone areas are scanned first
Flood risk mapping has started 2008 in Finland

4. A guidebook for flood risk mapping in Finland
A guidebook for flood risk mapping in Finland will be published in September 2008.
The guidebook on flood risk mapping describes the most important methods of flood risk mapping as well as the principal guidelines of flood risk mapping carried out by the environmental administration in Finland.
The publication has been compiled by EXTREFLOOD II project by the Department of Geography at the University of Turku and the Finnish Environment Institute
It was funded by two ministries – the Ministry of Agriculture and Forestry and the Ministry of the Environment – and coordinated.

5. A guidebook for flood risk mapping in Finland
The intention is to carry out the mapping process using the flood information system together with existing GIS materials and databases, i.e, without major new survey operations.
The final maps and the GIS-based map generator will be included in the flood information system of the environmental administration.
As for the visual expression of the maps, the objective is to make them unequivocal and easy to read.

6. Flood risk maps; available material

7. Flood hazard map

9. RHR
Building database
Building
Building,
flood depth > 1m

10. The number of inhabitants in flood area

13. An example of statistics from the databases

14. Visualization of flood risk maps
It is a major challenge to give the flood risk maps such a visual expression that each ”risk layer” can easily be seen
The appearance of the flood risk maps will probably still develop and the final versions are likely to be different from those presented here
The user of the flood information system will be able to choose the most appropriate flood risk maps as map layers in the GIS environment, by using the visualizations made in advance

15. Flood map production procedure in Finland
Flood hazard maps are produced by the local environment centres
Information is stored in the flood information system in SYKE
Available as pdf-maps and thru GI-system
Flood risk maps
SYKE use the available GI-data to produce preliminary flood risk maps for the mapped flood hazard areas
local environment centres check, correct and complete the data
Information is stored in the flood information system
Some towns have their own maps (like Helsinki for sea flood)