When flooding refers to a condition in which a normally dry lying bottom surface is completely covered by water. In addition to particularly strong earthquakes, flood disasters have so far been the most serious natural disasters for people .
Causes of flooding
Floods are mostly natural events:
- Storm surges push seawater over river mouths where there are no barriers , deep into the inland and over dykes on the coast and on coastal river sections or cause dike breaches ; Tsunamis can also flood high coastal areas that are not protected by dikes;
- Inland water overflows its banks during floods if the water does not flow “downwards” quickly enough (as surface water down into the valley or on unsealed soils into the groundwater). The flood can be caused by heavy rainfall, but also by the breakage of dams or dams due to excessive water pressure.
- Glaciers prevent inflowing water from flowing away and in this way form an ice reservoir .
- Filling groundwater reservoirs lead to rising water levels when the groundwater lies above impermeable soil layers. It then finds its way into deep-lying parts of buildings from below or (below the surface of the earth) from the sides. This mainly affects areas with a constantly high groundwater level.
The inadequate, sometimes non-existent drainage of large amounts of water inland and on islands can (at least in part) be caused by humans:
- The sealing of large areas makes it more difficult for surface water to seep away, which enters streams and rivers unchecked. However, heavy rain itself seals deeper areas, as it prevents the ability to absorb water even in soils that are not sealed at a certain point in time;
- The straightening and narrowing of rivers leads to an increase in the flow velocity of the water, which quickly reaches deeper areas and there runs into slower flowing water at narrow points. In metropolitan areas in particular, there are too few areas in which the water can spread. This inevitably leads to flooding when there is a strong influx of water due to heavy rainfall and / or surface water moving in large quantities.
- Collapsed structures or floating debris can jam on bridges , barrages , rakes or overflows or drains and thereby cause water to accumulate ( blockage );
- Floods (mostly locally limited) can also occur at great distances from larger rivers. In most cases, heavy rainfall ensures that the sewer system and drainage ditches cannot cope with the water masses. Facilities created for the temporary storage of water masses such as rain retention basins or planned flood plains often turn out to be undersized. In the cases mentioned, one of the main reasons for floods to occur is that the probability of occurrence and the effect of heavy rain events are underestimated;
- Although floods are a force of nature, flooding is not a “natural event” if it was caused by a burst water pipe or if areas (particularly in connection with armed conflict) are deliberately submerged.
In general, the question arises as to whether damage caused by flooding on built-up properties is “fateful” for the injured party if flooding through adjacent bodies of water or inadequate drainage systems can be foreseen due to the location of the damaged area. Builders should also be aware of the risk they run when they build systems below the ground in an area with a high water table.
Harmfulness of floods
Floods can cause significant water damage to people's property and endanger the health and life of people and farm animals. If there is such a danger, rescue workers speak of a water emergency . A distinction must be made between temporary flooding, which ends when the penetrated water runs off or is pumped up, from permanent flooding. The latter particularly threaten low-lying coastal areas as a result of the climate-induced rise in sea levels .
However, not every flood is a problem for people. For example, in desert areas without the regular overflow of rivers such as the Nile, apart from oases, there is no fertile land for arable farming and horticulture , and from an ecological point of view, natural wetlands that are regularly flooded are rated as extremely valuable.
In Germany, too, there are cultural landscapes whose inhabitants owe their prosperity to the fertility of their land, which in turn can be explained by sediments that were left on the ground after floods. This applies, for example, to the Artland , which is largely located in the Hase Inland Delta .
The term flood as economic damage is at the same time a legal term that is particularly relevant in connection with building, household, motor vehicle partially comprehensive and business interruption insurance. If this insurance provides protection against natural hazards, the risk of flooding is usually also covered. For the purpose of risk assessment and thus premium calculation, the General Association of the German Insurance Industry has developed a geographical information system: the zoning system for flooding, backwater and heavy rain (ZÜRS). The basis is statistical calculations by the software company IAWG (engineering hydrology, applied water management and geoinformatics) in Ottobrunn.
According to the Federal Court of Justice, the term “flood”, ie “flooding of the land on which the insured building stands (insurance property)” is to be interpreted from the perspective of an informed policyholder. According to this, the "flooding of the ground" is to be assumed when considerable amounts of water accumulate on the surface of the site. In contrast, the Dortmund Regional Court ruled that it was necessary that the normally dry area be a floor area in the sense of an area level with the ground. Flat roofs or balconies are not considered to be "floor areas" because they are not level. Damage caused by (dew) water penetrating the roof is therefore not covered by building insurance. There is already a lack of flooding, unless there is an accumulation of water on the surface of the site. Flooding of terraces is also not considered as insurance damage (despite the fact that it is level with the ground). The LG Nürnberg-Fürth defines the term flooding further.
- Axel Bojanowski: Ten facts about the flood . Spiegel Online . 6th June 2013
- Heavy rain: the underestimated danger . Film documentary. N3 . October 7, 2019. 45 minutes.
- Information from the GDV ( Memento from June 10, 2016 in the Internet Archive ), General Association of the German Insurance Industry
- Page no longer available , search in web archives:
- BGH, ruling v. April 20, 2005 - IV ZR 252/03.
- LG Dortmund, judgment of July 4, 2012 - 2 O 452/11.
- LG Nuremberg-Fürth, judgment of July 26, 2012 - 8 O 9839/10.