Flood control
Under flood protection is defined as the sum of all measures to protect the population as well as of property against flooding. These may be technical measures, natural retention of water volumes and measures of further preventive action ( three-pillar strategy).
Technical flood protection
The technical flood protection composed in particular for rivers in an emphasis in the areas of retention and property protection. Possible instruments for containment are flood retention basins of different types and flood areas (polders). This store large amounts of water and are thus able to reduce the peak discharge of flood waves.
Measures for property protection are structures along the body of water, to prevent flooding during proliferation in vulnerable areas such as settlements, infrastructure, industrial areas, etc. penetrate. These include flood levees ( dikes ) and protective walls as stationary constructions, but also mobile elements that are installed in case of a flood warning or effective in the form of locks.
Currently there is no location-independent deployable mobile flood protection system, which has a building approval. Nevertheless, various systems have proven in scientific studies as well as in the practical test.
Natural support
Depending on the size of the catchment area of a water body and the precipitation conditions have human land use and river development to a worsening of the flood situation by increasing the surface runoff and reduced retention in the floodplain (natural flood plains ) of the water at.
Often referred to as soil sealing is the cause of increased surface runoff, but also the intensive agriculture can make a significant contribution to increased runoff. The fact that even on unsaturated soil surface runoff occurs, is not to be justified in the size of the pore spaces, but is due to the permeability of the uppermost millimeters of the bottom surface. There, the soil structure is often impermeable in rain events by capping. Added to abflussbeschleunigende interventions in the natural balance of the river system as bank protection and river regulation.
In particular, long-range embankments themselves of agricultural land as well as weirs and dams have you done the rest to the fact that in many parts of Europe and North America floodplains as natural retention areas (natural flood plains ) and complex ecosystems have disappeared from the landscape.
Incentive mechanisms such as funding for more extensive agricultural land use concepts, measures for unsealing of areas, decentralized stormwater management in urban areas and the promotion of natural water development, such as river restoration, dike relocation and Auenvernetzung, an attempt is made to increase the natural retention again.
Further precautionary
In this field of flood protection all measures are summarized, which serve as the general care and organizational- technical measures in the event of a flood. These include the establishment of flood warning centers, the official designation of floodplains, to prevent development of hazardous areas in advance, as well as the establishment of emergency and disaster plans. However, water power plants can be designed so that they provide flood protection through its backwater assets.
Protection goal
The dimensions of floods are classified according to their so-called return period corresponding to the statistical recurrence interval. This means that e.g. a 100 - year flood event ( flood of the century, HQ100 ) statistical average returns every 100 years. However, this does not exclude that there have such a high water in two consecutive years. Protection goals for different areas are defined according to these recurrence intervals. For larger, built-up areas in general, the 100 - annual recurrence interval shall prevail. For smaller settlements and individual properties one goes in the meantime often means more than to define the objective of protection depending on the potential for damage, so that the cost of protective measures will not exceed the potential harm. A common guideline is the HQ30.
Main goal but continues to be the protection of life and limb against the effects of flooding. After the Second World War, agricultural land against floods with a recurrence interval of 5-10 years were protected in many parts of Germany. From this practice, but refrained for some time and dismantled older plants.
Netherlands
The Parliament of the Netherlands after the devastating floods of 1953, when large parts of the country were under water, determined that protection against a 1,250 - year flood must be achieved. This level of protection applies to both rivers and the coast. The decision followed a thorough, scientific investigation and with the Delta Plan a technically and financially costly backup program. The specified level of protection was achieved 30 years later with the completion of major coastal buildings everywhere. Currently Check the Netherlands, if the dimension of the 1,250 - year flood must be adjusted upwards by climate change, ie global warming and / or increased climate extremes, the previous estimates. Then, the protection should be further strengthened.
USA
In the U.S., flood protection by competent U.S. Army Corps of Engineers was set at the level of a 230 - year flood. This level is also ensured, however the flooding of New Orleans, has led to the realization that this level of protection is not sufficient.
Austria
In Austria the following safety objectives will be pursued:
- HQ30 Child Objects
- HQ100 standard protection
- HQ150 degree of expansion torrent ( torrents )
Any additional levels of protection are in need of special protection (eg for the City of Vienna) sought.
In all flood protection measures should be noted however, that there is always a residual risk (Appendix failure, exceeding the design flood ).
Germany
In Germany, the Federal Water Act stipulates areas that one time in a hundred years can be flooded statistically, to be reported as flood plains in official maps and to take in the planning. In such floodplains further rules are adopted according to the state laws or municipal regulations. Thus, for example, during interventions, the appropriate authorities consulted. The urban land or the water authority may take measures, such as a building expansion or reforestation, also ban on private land. Flood endangered areas ( HQ> 100, eg failure of a dike ) are to be marked in Germany also. The community is encouraged to inform the public of these dangers so that a private pension is possible. In order to avert the danger of buildings, is for builders but not the obligation to technical evidence from flood loads. Comparable binding rules in the wake of a building permit, similar to the prevention of risks from wind loads are not applied. Private engineering evidence is limited to the determination of expected water levels and flow rates to a greatest expected flood in over one hundred years. The impoundage and Anströmungsgeschwindigkeiten of water loads on a structure are basis for flood- safe planning and building.
Statutory rules on the level of protection does not exist. There is only one ruling of the Federal Court that homeowners with flood damage a public liability claim against the carrier for flood protection have, if the protection is not least ensured against a 50 - year flood. This minimum level of protection has been largely achieved ( also because of this case law ).
On the Upper Rhine to Basel, there is a protection against a 100 - year flood. In the Upper Rhine Graben formerly was a protection against a 200 - year flood. Through the expansion of the Upper Rhine by France but huge meadows were lost along the former natural river course. Therefore, a tidal wave of Basel to Mannheim requires the mouth of the River Neckar, instead of about 72 only about 36 hours, so that the superposition with the tidal wave of the Neckar is possible for large-scale heavy rains. The protection level has dropped to a 100 - year flood, which was almost reached in 1999. It was therefore decided in a 1982 treaty between France, the Federal Government and the states of Baden -Württemberg, Rhineland -Palatinate and Hesse, the level of protection by dike elevations, dike reinforcements and construction of polders back to a 200 - year flood to raise ( Integrated Rhine Programme). The program is to be completed by 2019, but increased in part from legal, partly for financial reasons. Responsible for the coordination of flood protection measures in the Upper Rhine is the Permanent Commission. For research and for environmental protection of the riparian, the " International Commission for the Protection of the Rhine" (ICPR; ). The ICPR has also issued a flood Atlas Rhine, which contains the main findings and previously defined desired protection goals. The Atlas identifies all areas that are flooded during a 200 - year flood.
Against the background of climate change and the outdated climate data ( calculation bases ) is also in Saxony now sought, for example, to derive flow rates of HQ200 harmless.
In a severe flooding in southern and eastern Germany in May / June 2013 showed that after the flood of August 2002 ( Elbe flood 2002 Danube flood in 2002 ) measures taken are effective. Among other things, the Department of Hydraulic Engineering and Water Management of the Technical University of Munich research on flood protection.
Bavaria has spent or invested since 2001, about 1.6 billion euros for flood protection; 2020 a further 700 million euros are planned. Approximately 400,000 people were also protected according to Bavarian State Office for the Environment ( LfU ) ever since. Dikes were repaired at 420 km; approximately 760 km river segments were renatured. The LfU also operates the flood news service Bavaria.
Special Structures
Germany:
- The flood protection dike Neuwied on the Middle Rhine, built in the years 1928-1931
- The Eidersperrwerk at Tonning
- The Hunte barrage
- The Ems barrier at Gandersum
- The Sylvensteinspeicher
Austria:
- Danube Island - Wiener_Donauregulierung
England:
Italy: