Mikko Sane, Tanja Dubrovin, Mikko Huokunafirstname.lastname@environment.fi Finnish Environment Institute, P.O. Box 140, 00251 Helsinki, Finland

www.environment.fi/syke www.environment.fi/floodmapping

A GIS based approach for flood risk mapping – extending the national flood information system

EXTREFLOOD II – the flood risk mapping pilot

EXTREFLOOD II research project aims to develop meth-ods, which enable more effective flood risk assessment in Finland.

One of the main objectives is to develop flood risk map-ping as a part of the national flood information system.

According to the flood directive (2007/60/EC) flood risk maps should indicate potential adverse consequences of flooding under several probabilities as a minimum in terms of

indicative number of inhabitants potentially affected,type of economic activity of the area potentially affected,installation which might cause accidental pollution in case of flooding andpotentially affected protected areas.

•

•

•

◦◦

◦

◦

The national flood information system of Finland, estab-lished in 2006, brings together the essential information on floods under a single user interface. The system is based on GIS and Web technology and contains various types of flood information. It promotes flood risk assessment, flood-proof land use planning, and rescue operation planning. Evidently, it increases public awareness about flood risk and ensures that the experiential flood knowledge is trans-mitted for the younger generations. Interactivity with oth-er information systems and GIS datasets eases the mainte-nance and provides a basis for further needs, such as de-velopment of flood risk maps.

Flood information types in the present flood information system

▲ An example of the user interface of the Flood Information System.

◄ Types of flood information in the Flood Information System and formats of the information. The arrows denote the processing of the information in flood mapping and flood management.

Flood mapping provides a good foundation for efficient flood-risk management.

Flood observations (water level and discharge)

Historic �ood maps

Simulated �ood scenarios (water level and discharge)

Flood hazard maps

Dam break �ood hazard maps

Minimum allowed building site levels

Point

Polyline

Polygon

Point

Point

Polygon

Polygon

Polygon

Flood Vulnerability

Flood Hazard Map

Flood Risk Management PlanFlood Risk Map

The town of Pori is located at the mouth of the Kokemäenjoki river in the southwest Fin-land. About 15 000 people is living in the flood prone area. The river is known for harm-ful winter floods. There used to be ice break up jams almost every spring in Pori, but the risk for spring ice jams decreased after the watershed regulation was started about 40 years ago. However, the climate change studies imply that winter discharges are going to increase significantly in the river. The available regulation capacity may be too small in order to decrease discharges and by this way to avoid the problems caused by frazil ice during the cold winter periods.

Town of Pori – the most significant flood risk area in Finland

► Ice jam in the centre of Pori in January 1975. Large areas were flooded, caused a lot of dam-age for housing and industry, because of a partial ice break up after a warm and rainy winter period (Photo: Kari Syrjälä).

Flood hazard map of Pori (on general back-ground map). Flood hazard maps show the ar-eas which could be flooded including the prob-ability of flooding and the degree of danger (in Finland usually water depth). Usually produced flood scenarios in Finland: 1/20a, 1/50a, 1/100a, 1/250a and 1/1000a.

Initial GI-data for flood risk mapping in Finland

Flood hazard mapa fundamental information for flood risk mapping

SLICES - Separated Land Use/ Land Cover Information System

more classes in the built up area than in the CORINE Land Cover

Building and apartment database (RHR)e. g. purpose of use andnumber of people living in apartment

Environmental database (VAHTI)activities which require an environmental permit licensewill or may cause environmental pollution or degradatione. g. IPPC-activities (Integrated pollution prevention and control directive 96/61/EC) andwater intake structures

Nature protection databasee. g. Natura 2000 –areas related to the Water Framework Directive (EU-wide network of nature protection areas)

Other national databases, e.g. ground water areas (POVET), polluted soil (MATTI), topographic database (e. g. electricity network), beaches (EU) and cultural heritage

Local vulnerability informationall the information cannot be found from the databases

•◦

•

◦

•◦◦

•◦

◦

◦

◦

•◦

•

•◦

Examples of flood risk/vulnerability layers

Statistic as tables to the database for each flood scenario from each areaHQ 1/250,sea level N60+0,40 m- Areas (ha) of land use of each SLICES land use type 0

-0.5

m

0.5-

1 m

> 1

mFl

ood

prot

ecte

d ar

ea

To

tal

HQ 1/250,sea level N60+0,40 m- Number of buildings of each type (RHR) 0

-0.5

m

0.5-

1 m

> 1

mFl

ood

prot

ecte

d ar

ea

To

tal

Apartment house area 7 15 2 10 34 Detached houses 627 891 615 1 034 3 167Small-house area 95 141 96 164 497 Row houses 14 68 109 118 309Holiday cottage area 11 23 13 0 47 Apartment houses 22 36 2 29 89Sport and leisure facilities 23 40 56 20 140 Holiday cottages 79 239 51 1 370Commercial ja administrative units 7 6 1 12 25 Commercial, of�ce and transport 45 55 33 84 217Industrial and depot units 17 11 4 19 51 Health care 3 5 1 0 9Transport units 38 25 8 20 91 Sport and leisure 9 4 1 9 23Community management units 6 9 6 6 27 Educational buildings 7 1 0 6 14Agricultural areas 452 871 921 101 2 345 Industrial buildings and depots 43 38 14 50 145Forest areas 154 220 194 146 715 Fire and rescue services buildings 0 0 0 1 1Total of each water depth zone 810 1 361 1 302 498 3 971 ha Agricultural buildings 7 6 1 5 19

Other buildings 197 263 194 331 985- Number of inhabitants (RHR) 998 3 617 5 766 5 153 15 534 inhabitants Total of each water depth zone 1 053 1 606 1 021 1 668 5 348 buildings