Flood hazard maps (Polish abbreviation “MZP”) and flood risk maps (Polish abbreviation “MRP”) are drawn up on the basis of the following legal acts:
- Directive 2007/60/EC of the European Parliament and of the Council of 23 October 2007 on the assessment and management of flood risks (Floods Directive);
- Water Law Act;
- Regulation of the Minister of the Environment, Minister of Transportation, Construction and Maritime Affairs, Minister of Administration and Digitization, Minister of Internal Affairs of 21 December 2012 on the development of flood hazard maps and flood risk maps (Journal of Laws of 2013, item 104), hereinafter referred to as the regulation.
In accordance with the Water Law Act, the President of the National Water Management Authority is responsible for the preparation of maps. However, flood hazard maps and flood risk maps for sea waters, are prepared by the directors of maritime offices.
The implementation of the Floods Directive in the 1st planning cycle occurred by drawing up:
- the preliminary flood risk assessment (Polish abbreviation “WORP”) by 22 December 2011,
- flood hazard maps and flood risk maps by 22 December 2013 (publication and delivery of the maps to authorities occurred on 15 April 2015),
- flood risk management plans for river basin districts by 22 December 2015 (regulations on flood risk management plans of 18 October 2016).
Flood hazard maps are prepared for the areas with potential significant flood risk indicated in the preliminary flood risk assessment, i.e. areas where there is a significant flood risk or the occurrence of flood is likely.
Flood hazard maps and flood risk maps form a basis for the development of the flood risk management plans and for planning technical and non-technical flood control measures, which aim to reduce potential adverse consequences of flooding for human health and life, the environment, cultural heritage and economic activity.
The Floods Directive (art. 14(2)) states that flood hazard maps and flood risk maps shall be reviewed, and if necessary updated, by 22 December 2019 and every 6 years thereafter.
The new Water Law Act of 20 July 2017 (Journal of Laws, item 1566), which shall come into force on 1 January 2018, maintains the validity of the flood hazard maps and flood risk maps prepared during the 1st planning cycle (art. 555(2), paragraphs 4 and 5) and orders their review by 22 December 2019 and update, if necessary.
The new Water Law Act (art. 169-170) specifies the general scope of flood hazard maps and flood risk maps. However, the specific scope and requirements for the development of flood hazard maps and flood risk maps, as well as the scale, are determined by the Regulation.
Flood hazard maps shall cover the geographical areas which could be flooded according to the following scenarios:
- areas, in which the probability of flood occurrence is low and amounts to once a 500 years (Q 0,2%),
- areas, in which the probability of flood occurrence is medium and amounts to once a 100 years (1%),
- areas, in which the probability of flood occurrence is high and amounts to once a 10 years (Q 10%);
- areas covering the land exposed to flooding in the event of:
- destruction or damage of the river embankment,
- destruction or damage of the storm embankment,
- destruction or damage of the damming structure.
In addition, flood hazard maps should include:
- water depth,
- water velocity and water flow directions – for voivodship cities and cities with poviat rights, as well as other cities with a population above 100 000 people.
Flood hazard maps should include the depth and velocity of water in the classes defining the level of risk for people and the impact of water on buildings, in accordance with the Regulation:
- depth of water:
- h ≤ 0,5 m – indicating low risk for people and buildings;
- 0,5 m < h ≤ 2 m – indicating average risk for people due to the possibility of escaping to upper floors, but high risk due to material lossese;
- 2 m < h ≤ 4 m – windicating high risk for people; flooding may occur not only in ground floors, but also first floors;
- h > 4 m –indicating very high risk for people and very high risk of total damages;
- water velocity:
- v ≤ 0,5 m/s – low velocity – water has a small impact on buildings;
- 0,5 m/s < v ≤ 1 m/s – average velocity – water has a moderate impact on buildings and is able to move small and light objects, poses a threat to people;
- 1 m/s < v ≤ 2 m/s – high velocity – water has a strong ability to impact buildings, may move relatively large and heavy objects, poses a serious threat to people;
- v > 2.0 m/s – very high velocity – water has a very strong ability to impact buildings, may move very large and very heavy static objects, poses a very serious threat to people.
In accordance with the regulation, cartographic versions of flood hazard maps are prepared in two thematic sets:
When talking about the areas where the probability of flooding is e.g. 1 % (that is, once every 100 years), it should be understood that the computation uses the water discharge (maximum) with the 1% probability. These discharges are calculated on the basis of maximum annual discharges for multi-annual datasets (at least 30 years) for a given water gauging station. The maximum discharge with the likelihood of 1% means that statistically this flow may appear in a given section once every 100 years. It does not mean that flood with the 1% probability occurs at intervals of one hundred years. It should be noted that this value is statistical, but based on historical data.
Fragment of a flood hazard map with the water depths
Fragment of a flood hazard map with the water velocity and water flow directions
Flood hazard areas shown on maps are the result of mathematical hydraulic modelling. The process of modelling uses highly accurate spatial data, acquired through air laser scanning, i.e. a digital terrain model which spatial accuracy amounts to 10-15 cm, as well as a digital surface model. For the purpose of drawing maps, also new hydrological data, including flood events of recent years, are developed
Due to the use of new, more accurate input modelling data, flood hazard areas may differ from the areas indicated in the flood protection studies created previously by the directors of regional water management board. It should be noted that flood protection studies for river sections, for which flood hazard maps were not prepared in the 1st planning cycle, shall remain valid until the preparation and delivery of flood hazard maps to competent authorities, drawn up in the next planning cycles..
Flood risk maps are drawn up for areas included in flood hazard maps.
Flood risk maps define the value of potential losses and present objects exposed to flooding in the event of a flood with a specified probability. These are objects that allow a flood risk assessment for health and life of people, the environment, cultural heritage, economic activities, or for the group for which it is necessary to limit the negative effects of flooding in accordance with the Floods Directive.
For this purpose, flood risk maps include, in particular:
- The indicative number of inhabitants potentially affected; Residential buildings and objects of special social interest, whose operation can be difficult or impossible due to flooding, i.e. hospitals, schools, kindergartens, nurseries, hotels, shopping malls, social care centres, hospices, prisons, correctional establishments, jails, police units, fire-fighter units; For each residential building or object of special social interest, there is an estimation of the average depth of flooding separately for each flood scenario, classified in two ranges:
- water depht less than or equal 2m,
- water depht graeter than 2 m.
The limit value of water depth (2 m) has been assumed in relation to assumed brackets of water depth and their influence on a degree of threat to people and building structures.
- Types of economic activities in flood risk areas in the form of land-use classes:
- residental areas,
- industrial areas,
- communication areas,
- recreaton areas,
- agricultural land: arable land and grassland,
- water areas,
- Cultural heritage areas and buildings;
- Installations that, in the event of floods, may cause significant pollution of individual natural elements or the environment as a whole:
- installations or installation units, where it is required to obtain an integrated permit within the meaning of art. 181(1), paragraph 1, of the Act of 27 April 2001 - Environmental Protection Law (Journal of Laws of 2008, item 150, with further amendments), in the following categories of industrial activities: energy industry, manufacture and processing of metals, mineral industry, chemical industry, waste management, other types of activities, including manufacture and processing of paper and wood, intensive farming or breeding of pigs and poultry, manufacture and processing of plant and animal resources;
- industrial plants that do not require the permit referred to in paragraph 1, but which may pose a threat, including industrial where there is a high risk of failure or increased risk of failure within the meaning of art. 248(1) of the Act of 27 April 2001 - Environmental Protection Law;
- Protected areas:
- water intakes – including water intended for people,
- protection zones of water intakes,
- bathing zones - included in the list referred to in art 34f(2) of the act – Water Law (designated under Directive 76/160/EEC),
- Natura 2000 areas,
- national parks and nature reserves,
- Potential outbreaks of water pollution in case of flooding, i.e. industrial plants, wastewater treatment plants, wastewater pumping stations, landfills, cemeteries;
- The degree of potential losses for individual classes of land use, i.e. residential areas, industrial areas, communication areas, forests, recreational areas, arable land, water areas.
In accordance with the Regulation, cartographic versions of flood risk maps are prepared in two thematic sets:
- Flood risk map – negative consequences for people and the degree of potential losses,
- Flood risk map – negative consequences for the environment, cultural heritage and economic activity, separately for each flood scenario.
Fragment of a flood risk map – negative consequences for the environment, cultural heritage and economic activitys,
Fragment of a flood risk map – negative consequences for people and the degree of potential losses
Flood hazard maps and flood risk maps as planning documents represent in practice nontechnical means for protection against flood aiming at limitation of potential negative effects of flood. The aim of creation of these documents is proper management of risk which flood may create for life and health of people, environment and economy.
Access to information on areas threatened with flood and the level of such a threat as well as indication which risk is related to occurrence of flood in a given area, will certainly contribute to making aware decisions in respect of location of investments by inhabitants and by local authorities. Each citizen may check if the area in which he / she lives in threatened by flood and if so to what extent it is threatened.
The maps constitute the basis for rational spatial planning in the areas threatened by flood and thus for limiting negative effects of flood.
Information contained in the maps is also useful in responding and in managing crisis in the event of flood. The maps may represent an initial point for preparing further analyses necessary to complete actions of various administration authorities, including crisis management.
However, the main purpose of the development of flood hazard maps and flood risk maps is comprehensive development of flood risk management plans – the final stage of the implementation of the Floods Directive. These maps will be an efficient data acquisition tool, the basis for establishing priorities and making further technical, financial and political decisions associated with flood risk management.