The Kymenlaakso Region 

The Kymenlaakso region (the River Kymi Valley) is located in south-eastern Finland with a population of approximately 180 000. The main cities are Kouvola and Kotka. The city of Kotka is located at the delta of the river Kymijoki. Together with the neighbouring city of Hamina, they have the most important harbour in Finland. The Port of HaminaKotka is the largest universal, export, container and transit port in Finland, with regular connections to all major European seaports. The city of Kouvola is Finland’s tenth largest city with about 88 000 inhabitants. Industry is a major employer in the city, although the region’s forest industry has drastically declined in recent years. These days, an increasing number of people in the city are employed in commercial services.

Although the economic development of the Kymenlaakso region has been favourable, the population has been decreasing for a long time. A large number of young and working-age people have moved away from the Kymenlaakso region, mainly to the Helsinki Metropolitan Area. This migration has distorted the population's age structure; the share of working age people has decreased and the relative share of the elderly has increased.  


Despite its fairly small geographical size, the landscapes in the Kymenlaakso region area are diverse. The Gulf of Finland, the River Kymijoki and the Salpausselkä formations divide the region into the archipelago and coastal district, the eastern topographically varying hill district, the western clay-soil district and the northern wilderness and lake district. The archipelago is characterized by rocky shores, large islands with forests, and steep cliffs. The rich variety of nature and landscape is also indicated by the fact that there are three national parks. The River Kymijoki is over 200 km long and is one of the largest rivers in Finland, with a drainage basin covering 11% of the area of the country. 



Identifying hazards and estimating potential risks

Storm water flooding or flash floods occur during heavy, long lasting rains or short but very intense rain events. Factors contributing to storm water flooding include soil sealing with impervious pavement types, such as asphalt, bricks, stones or concrete. Especially growing cities with a large amount of new construction are vulnerable to storm water flooding due to the increase in paved areas. Geology has similar effect to paving in connection with intense rain events. Very fine grained or tightly packed sediments, such as thick clay layers or tightly packed moraine, as well as bedrock are not able to infiltrate rain water fast enough to the ground, leading to flash floods. To estimate how prone the study area is to storm water flooding, the hydraulic conductivity of soil types, the percentage of soil sealing and slope steepness were combined on 20 x 20 m raster maps. Then maps were classified into eight different classes according to the combination of qualities they possessed. '0' is the class for the highest infiltration capacity / lowest storm water flooding potential (green colour on the map) and '7' for the lowest infiltration capacity / highest storm water flooding potential (blue colour on the map). Bedrock areas and watercourses were excluded from the classification at this point. Sewerage and vegetation type or existing flood management structures were neither taken into account in this estimation.

Map analysis

In the Kymenlaakso region, the areas prone to flooding are the city centres of Kouvola, Kotka and Hamina, and surroundings of the River Kymijoki. The impact of geological characteristics on this hazard can be clearly identified from the generated map. Across the Kymenlaakso region from west to east run two large end moraine formations (Salpausselkä I and II). On their southern sides, the sediments are dominated by fine-grained material compared to the northern side. This can be seen as an increased storm water flooding potential, especially south and southwest of the city of Kouvola. 

In the Kymenlaakso region, over 15% of the area designated with a land use in the regional plan has low risk potential for storm water flooding, 34% has a medium risk potential, 8% a high risk potential and only 0.1% has a very high risk potential. 

In the future, the annual average precipitation is estimated to increase, and during warmer winters even more precipitation will be as water instead of snow. This would also mean a higher potential for winter storm water flooding. Since geological factors such as the soil type or the slope of the ground surface of our living environment cannot be mitigated, the areas that are prone to storm water flooding will most probably be the same in the future. As the areas highly prone to storm water flooding add up to almost 18% in study region, this is an issue that should be continuously taken into account when planning new areas. 

Note! The separate map of soil infiltration capacity for the city of Kotka is also provided. Risk map is based on regional land use plan. 



Kotka_Generalised_Infiltration_Capacity_of_Soil.pdf (includes outer islands)



Kotka_Generalised_Storm_Water_Flooding_Risk.pdf (includes outer islands)



Kotka_Generalised_Slope_steepness_for_runoff_potential.pdf (based on DEM25m)



Surface water flooding and especially river floods usually occur during spring when snow accumulated during the winter months melts. Spring floods will decrease in southern Finland in the future due to climate change, but floods during the other seasons might increase. In southern Finland, the change in precipitation is the main factor affecting flood patterns. Warmer winters may also increase frazil ice phenomena in rivers. Rivers in southern Finland are of varying sizes. The largest is the River Kymijoki. The smallest have only local significance. Large lakes and rivers may also be regulated with dams or their level may be kept within certain limits to protect agricultural areas around the watercourse. Although the most significant river flood areas have been defined, this does not mean that the other rivers are not prone to flooding.

Map analysis

In the Kymenlaakso region, surface water flooding mainly occurs in the River Kymijoki. For other main rivers (Nummenjoki, Summanjoki, Vehkajoki, Pyölinjoki, Virojoki) located in the region, no flood modelling is available. Therefore, the surface flood hazard for the Kymenlaakso region is only based on flood modeling data for the River Kymijoki.

A typical feature for the River Kymijoki catchment area is the large number of lakes. Many of these lakes have regulated flow, which has a considerable effect on the floods in this area. Another feature that causes floods is frazil ice dams on the river part that is located south of Anjala. The flood depth class distribution in the Kymenlaakso region for the 1/100a floods indicates that shallow floods are more dominant than the deeper floods. For 1/250a floods, the proportion of deeper floods increases substantially. This could be due to low-lying areas existing next to rivers and lakes, which instantly turns shallow floods into deeper ones when the water level rises. The soil type in the surroundings of the river valleys is mainly clay, so the infiltration capacity is very low. In addition, the amount of soil sealing is very low.

In the Kymenlaakso region, the potential risk due to surface water flooding is mainly low or medium (values '1' and '2'). The flood-prone areas of the River Kymijoki mainly consist of nature protection, agriculture and forestry, and recreational areas. These land use classes are not considered to be at risk in a similar manner to different urban land use types in the case of a flood event.

Note! The surface water flood maps are under continuing updates, and level of detail may vary depending on the time when the dataset is uploaded from the site.











Storm surges in Finland are mainly caused by rapid sea level rise. Causes include low air pressure in the area, internal oscillation caused by a long-lasting heavy wind towards the north or north-east from the Baltic Proper, and heavy winds through the Danish straits. One important factor affecting storm surges is post-glacial land uplift. Until now, the land uplift rate has been higher than sea level rise, increasing the land surface in coastal areas. According to recent estimates of sea level rise, the future land uplift rate will not be able to fully compensate for sea level rise, as it will accelerate in the coming decades. Therefore, storm surges will become higher in the future, even if the land uplift rate remains stable.

Storm surges are expected to increase in the future along with sea level rise. According to the estimates, the flood levels will slowly rise from current situation to 2050, but the rate of rise will increase from 2050 towards 2100. In 2100, the 1/100a floods are expected to be similar to the 1/1000a floods of today. In addition to sea level rise, extreme weather events (especially strong, long-lasting westerly winds) are estimated to be more severe in the future.

Map analysis

The topography influences the estimated flood depth. In the Kymenlaakso region, the coastal areas are quite low-lying, which can also be seen from the distribution of the flood depth classes. From 2011 to 2050, there will be minor changes in the flood class distribution, but from 2050 onwards the change is expected to be stronger, and in 2100 the Kymenlaakso region will experience higher flood levels. Larger parts of the flooded area will be covered by deeper floods. In particular, the proportion of 2–3 meters deep floods will significantly increase.

The storm surges are considered to cause mainly low or medium risk potential (classes '1' and '2') in the studied timeframe. The land use of the areas prone to storm surges in the Kymenlaakso region comprises agricultural and forestry areas as well as nature protection and recreational areas. Thus, the high and very high risk potential (class '3' and '4') will not decrease significantly in the future, even though flood-prone areas are predicted to be more extensive. The most notable decrease can be seen in risk class 4 (i.e. very high risk potential) in 2100.

Note! The separate maps of the storm surge in 2011, 2050 and 2100 for the Kotka-Hamina are also provided. Risk maps are based on regional land use plan.













Integrated flood risk map was made by combining single flood risk maps of surface water flooding (1/100a flood), storm surges (1/100a flood 2011) and storm water flooding. The integrated geological risk results from the highest risk level given to one of the single risk, i.e. if value "4" is given to any raster cell it will result "potentially very high geological risk" within the integrated geological risk map. In this evaluation, all factors are equally important and no weighting is implemented.

Map analysis

In the Kymenlaakso region, the integrated risk map is dominated by the storm water flooding risk, as it covers the largest area of the flood types presented in the area. Highest risk potential is found in the municipal centres of the Kymenlaakso region. In the northern parts of the region, the centres of Iitti, Kouvola, Elimäki and Anjala can be clearly identified in the map. On the coastal area, highest risk potential is in the cities of Kotka and Hamina, not only due to high storm water flooding potential but also due to storm surges and surface water floods. The municipal centres of Pyhtää and Virolahti have a lower risk potential mainly due to less intensive land use.

In Kymenlaakso, the two highest storm water flooding risk classes ('3' and '4') cover approximately 143 km2 of the region. This is approximately 2.5 % of the total land area of the region. Same figures for surface water flood risk and storm surge flood risk for 2011 are 2 km2 and 13 km2, respectively. Storm surge risk area for classes '3' and '4' will increase to 20 km2 by 2100 according to current information.

Note! The separate map of the integrated flood risk for the city of Kotka is also provided. Risk maps are based on regional land use plan.



The construction conditions of soils may face unfavourable impacts due to climate change. In particular, changes in the soil frost period may cause unexpected challenges to existing foundation techniques. Heavy rains as well as changes in precipitation patterns, in snow cover and in groundwater conditions alter soil properties such as the bearing capacity and frost susceptibility. They may also contribute to landslides and erosion. In addition to changes in soil characteristics, changes in flood patterns will narrow the areas that are most suitable for construction purposes.

The geological characteristics affecting construction conditions were studied based on existing geological maps and data at the regional level. This evaluation was based on the general geotechnical characteristics of different soil types. The fine-grained component directly affects the soil permeability. Frost susceptibility properties and organic matter weaken the geotechnical suitability. The data were amended with information on slope steepness that has been calculated according to the airborne 3D laser scanning data of the National Land Survey of Finland (or alternatively the 25 x 25 m pixel-size digital elevation model).

Map analysis

In the Kymenlaakso region, over 40% of the land area is classified as a bedrock area. The characteristics of these areas for construction have not been considered. The most favourable construction conditions with sandy soil and low topography cover less than 10% of the land area. The favourable construction conditions with moraine and low topography cover about 15% of the land area. Demanding construction conditions with clay areas or areas with varying topography are nearly 30% of the land area. The most demanding construction conditions with soft organic soils such as peat and gyttja are about 8%.

Note! The separate map of construction conditions of soil for the city of Kotka is also provided. Risk map is based on regional land use plan.