Flood hazard zones, basic scenarios

Flood maps form the basis for effective flood risk management. Map-based information on flood hazard, vulnerability and risk is essential for flood risk management activities. Flood hazard maps increase the awareness of authorities and citizens of flood hazard areas. Flood maps can be used, for example, to draw up flood risk management plans, plan the use of areas, carry out rescue operations and provide information. For example, they can be used to plan activities in a flood situation, such as road closures and evacuations. The designated flood area consists of flood hazard zones that describe the flood-covered area caused by a certain water level and the degree of danger with a certain probability (repeatability time). Flood recurrence time refers to the average length of time before a flood of a certain size or size reoccurs. For example, the probability of a flood (1/100a) occurring once every 100 years in a selected year is 1%. So far, more than 100 river and lake areas have been mapped across the country. A seaflood survey has been prepared for the entire coastal area. The designated flood area is available as a spatial database for the repeated numbers 1/2a, 1/5a, 1/10a,1/20a, 1/50a, 1/100a, 1/250a and 1/1000a. Each recurrence has its own depth zone map layer. In addition to flood cover, they usually describe the water depth used as a degree of danger by zone (0-0.5 m, 0.5-1 m, 1-2 m, 2-3 m, over 3 m and water body). In addition, map layers are available on the boundaries of flood mapped areas, as well as information lines (crosslines), points and areas. The water level readings of different recurrences from flood-mapped areas are recorded here as an attribute. The water levels are shown from the 1D modelled area as lines (polyline), from the 2D modelled area as a point (point) and for lakes (stable water) as an area (polygon). When using the designated flood area, the reliability and accuracy of the initial data shall be taken into account. Flood maps are based on the best available information at the time of drafting, both in terms of topography and flood vulnerability. The recurrence period is based on the time when the flood map was drawn up. For older maps, it may no longer correspond to the current flood recurrence period. Flood hazard zones describe which areas are at risk of flooding with different levels of flooding. They do not directly indicate which buildings will get wet, because the ground level data used in the mapping differs from the actual lowest damage-causing height, such as the plinth height. On the other hand, basements, for example, can get wet even if the flood does not spread all the way to the building. This dataset includes watercourse floods (floods rising from rivers or lakes) in open water situations (ice not taken into account, recurrences of the flow of open water situations used) and sea floods. Other flood maps, such as flood maps for floods caused by ice and hyydepadoes, as well as flood maps that take into account simultaneous floods in watercourses and seas, can be found in some areas (see data on flood hazard zones, special scenarios). The impact of climate change has also been taken into account in some places. The data is included in SYKE's open data (CC BY 4.0). An INSPIRE data product has been published from the data. In addition, based on the data, the Future Floods INSPIRE data product has been published. Description of the material: https://geoportal.ympäristö.fi/meta/julkinen/dokumentit/MaaritetytTulvatVesisto.pdf https://geoportal.ympäristö.fi/meta/julkinen/dokumentit/MaaritetytTulvatMeri.pdf Further information: https://www.vesi.fi/tulvakartat https://www.vesi.fi/vesitieto/tulvakartoitus/ *** Brief in English Flood mapping forms a basis for efficient flood risk management. The flood maps can be used to support flood risk management planning, land use planning, reporting and as well as for rescue operations. The dataset includes information on areas covered by a lake or river flood (fluvial) and as well as sea (coastal) flood with a specific water height at the estimated risk level. The risk level is reflected a likelihood of a flood on the area. Flood frequency time presents the time period that apparent elapses between floods of at least the specified size. For example, the frequency rate of a flood occurring once in a century (1/100a) is 1% per a year. Defined flood hazard areas for sea floods are available with frequency rates of 1/2a, 1/5a, 1/10a, 1/20a, 1/50a, 1/100a, 1/250a and 1/1000a. Each frequency rate is packed with a separate map layer. Flood area maps include an estimation of flood coverage, but also water depth zones reflecting the hazard level (0-0.5 m, 0.5-1 m, 1-2 m, 2-3 m, over 3 m and a waterbody). Also map layers measuring outlines of flood mapped areas and infolines are included. The infolines, infopoints and infoareas have attribute data on water level of flood with different frequency rates. In the mapping of flooded areas, attention must be paid to the reliability and accuracy of the source information. Coarse scale flood hazard maps are not accurate enough for building specific inspection. The Finnish titles of the datasets are Flood hazard zones, fluvial floods and sea floods. Feature attribute description and UML-model: https://geoportal.ympäristö.fi/meta/julkinen/dokumentit/flood_hazard_river_lake.pdf https://geoportal.ympäristö.fi/meta/julkinen/dokumentit/Flood_hazard_sea.pdf Additional information and the flood map service: https://www.vesi.fi/en/water-topics/am-i-living-in-a-flood-risk-area/