Flood Precaution

The prevailing safety thinking is increasingly replaced by a culture of risk. It has been realised that the risk of extreme natural hazards cannot be reduced to zero and that disaster management has to be seen as closed loop. The mastering of a catastrophe leads over to precaution for the next event. Especially after the flood of 2002 many federal states in Germany worked out new plans for enduring flood protection, which are based on the three pillars natural support, technical flood protection and flood precautions.

Precautions can be distinguished between different domains, each with a different group of people and institutions involved.

• The aim of area precaution is to keep structural development out of inundation areas. The most effective way to limit the potential of damage in flood endangered regions is to keep areas clear of buildings. Besides, it is useful to secure retention basins as well as flood drainage in areas close to the banks. Within the scope of state-, regional-, and construction planning board the different administration levels of the Federal Republic of Germany decide about the usage of these areas.


• Private households and companies may reduce damage on already existing structures within inundated areas by reducing their damage susceptibility by building precaution. It works most effectively in areas with frequent flooding and small inundation depths.


• The basis for carrying out effective emergency measures is behavioural prevention. Every resident and every company in flood endangered regions should be informed about emergency plans (and what to do in case of a flood). Parts of the behavioural precaution are informative and (above all) timely flood warnings, which help to reduce damage shortly before the event happens.


• Risk precaution comes into use in the case of damages occurring despite all flood precaution arrangements. For a flood damage not to become existentially dangerous, financial provision is necessary. For that, different strategies are possible: private provision by saving capital, voluntary insurance-based private provision or the hoping for financial aid by private contributions and national financial aid programmes. National funds or a compulsory insurance provide a calculable indemnification for affected people.

The area precaution influences the degree and way of utilising flood endangered areas for different purposes. In Germany, this issue is controlled by the construction planning board on municipal level. The municipalities play the key-role in assigning building sites, whereas flood protection aims are in competition with other interests, e.g. the settlement of trade and industry. After the Elbe river flood in 2002, many federal states in Germany started generating hazard maps to improve the area precaution. However, a state-overlapping concept to mark flood endangered areas does not exist so that significantly different approaches are pursued. In many cases inundation areas with a recurrence interval of 100 years as well as for extreme events are provided. In most cases inundation depths and flow velocities are not mentioned.

Figure 1: Swiss model for preparing hazard maps	For instance the following German states published their hazard maps: Baden-Württemberg Bavaria North Rhine-Westphalia Saxony As an example, a model for generating hazard maps developed in Switzerland was adapted by the state of Saxony. This model classifies danger into four categories: serious, medium, minor and residual danger. They are calculated as a combination of intensity (water level and flow velocity) and probability of occurence. With this result it is possible to assign the different danger zones and to draw conclusions for regional planning.

In flood endangered areas with already existing settlements the potential of damage may be reduced either in short or long term by building precaution measures. The following strategies are therefore pursued: grouping or shielding, sealing or reinforcing, adapted usage and equipment of buildings as well as or securing of dangerous materials.

In detail this concept integrates installing permanent or mobile barriers to keep the water away from buildings and improving the stability of buildings to prevent buoyancy, water pressure and erosion. Furthermore the concept includes backwater protection and sealing of buildings as well as constructional elevation of openings and sealing arrangements to prevent surface- and groundwater from soaking in.

If water inlet cannot be avoided, the damage can be reduced by flood-adapted use of the building. This can be achieved by the following useful actions: an inferior use of the endangered floors; moving electric supply, heating, and maintenance utilities to the upper floors; safe anchoring of fuel-oil tanks; application of water-resistant and -persistent building materials; mobile furnishings.

Figure 2: Strategies of building precautions, source: adapted after IKSE 2003. Figure 3: Aarrangements to prevent water-inlet, source: Meike Mueller, Deutsche Rückversicherung.

• Hochwasserschutzfibel - Planen und Bauen von Gebäuden in hochwassergefährdeten GebietenBundesministerium für Verkehr-, Bau- und Wohnungswesen
• Hochwasserfibel - Bauvorsorge in hochwassergefährdeten GebietenMinisterium für Umwelt, Raumordnung und Landwirtschaft des Landes Nordrhein-Westfalen
• Hochwasserhandbuch - Leben, Wohnen und Bauen in hochwassergefährdeten GebietenMinisterium für Umwelt und Forsten Rheinland-Pfalz
• Hochwasser-Merkblatt für Bewohner gefährdeter GebieteStadt Köln
• KREIBICH, H., A.H. THIEKEN, T. PETROW, M. MÜLLER, B. MERZ (2005): Flood loss reduction of private households due to building retrofitting - Lessons learned from the Elbe floods in August 2002. - Natural Hazards and Earth System Sciences, 5: 117-126.

Basis of the behavioural precaution is the awareness of risk, because only who is aware of being threatened by a flood prepares for the case of an emergency. Tasks of the behavioural precaution are e.g. setting up emergency plans, carrying out exercises and drills, harmonising and actualising information chains, distributing booklets, and installing information boards. An essential requirement for increasing private precaution measures in flood-endangered households and companies is the communication about flood risks. For instance, flood marks remind of past flood events generally showing the highest historic tides and are usually installed on central and public walls. They are a possibility to keep alive and strengthen the perception of the existing flood danger.		Figure 4: Flood marks at castle Pillnitz, picture: Grünewald.

Since 1991 the "Extended Elemental Damage Insurance" hedges buildings and/or household effects against damages caused by floods. It is offered as a complementary insurance to every residential building insurance or household effect insurance. This insurance hedges also against damages caused by different natural hazards (earthquakes, heavy rain, etc.) to prevent that it is only demanded by those, who have a high risk of flooding damage. At present this type of insurance is no compulsory. A requirement for a plausible classification of an insurable object is a reliable estimation of the risk. Since there are no area-wide hazard maps for the whole of Germany, the insurance business developed a zonal system for inundations (ZÜRS). Besides the ZÜRS-zone the number of precedent damage cases as well as the distance to the water body is very important for estimating risks.

Further information:

• THIEKEN, A.H., TH. PETROW, H. KREIBICH, B. MERZ (2006): Insurability and mitigation of flood losses in private households in Germany. - Risk Analysis, Vol. 36 (in press).
• Hochwasservorsorge in Deutschland. Lernen aus der Katastrophe 2002 im Elbegebiet.Schriftenreihe des DKKV 29, 2003.