A dam with a barrier structure in a valley dams a flowing water to a reservoir ; The opposite valley flanks form the lateral support of the dam and the limitation of the storage space.
In the professional world, dam is understood as a generic term for all associated systems such as the barrier structure , the storage space , the extraction structures and the flood relief system . In common parlance, the reservoir is also included. Often only this is referred to as a dam.
The technical-professional definition is: A dam is a structural system for the damming of flowing water ( dam system ), which closes off the entire width of the valley beyond the cross-section of the watercourse. In contrast, a weir only closes the cross-section of a watercourse across its width. The storage space serves as storage ( DIN standard 19700-11).
This does not only include original barriers and weirs in mountain valleys . In the foothills and lowlands , too , water is dammed in so-called lowland reservoirs.
The legal definition can be found in the water laws of the federal states. As a rule, a dam system with a height of more than 5 m (measured from the top of the structure to the lowest point in the area in the storage facility) and a storage volume of more than 100,000 m³ is considered a dam.
Function of a dam
Dams serve the following main purposes:
- Drinking water supply ,
- Power generation ,
- Service water supply (industry and agriculture),
- Flood protection ,
- Low water rise ,
- Making navigable .
In addition, many reservoirs and their immediate surroundings are used for leisure and sports activities and for recreation . Furthermore, reservoirs can be used for fish farming .
Degree of expansion
The degree of expansion is an important parameter for the storage function of a dam . This is the storage volume of the storage space divided by the volume of the annual inflow. Well-equipped dams have a degree of expansion of 1.0 (100%) or more. But also dams with a degree of expansion of 0.3 (30%) are still able to significantly dampen floods and to increase low water to a limited extent. There are also dams with a degree of expansion of 1 to 2%, but these can hardly be used for storage management.
Classification of the barriers
A distinction is made between the following versions of the barrier structures :
The dam is made of rock and earth. The stability of the structure is given by its own weight and the flat slope angle. When it comes to sealing, a distinction is made between a surface seal and a core seal .
In the face seal of the dam on the water side, for example, a clay - or clay sealed. However, there are also other designs of this type of seal - such as asphalt layers . The disadvantage of this design is that the seal is exposed to the effects of the weather and shaft runout, and is therefore more likely to be subject to wear.
In the case of the core seal, there is a so-called sealing bar inside the dam. The disadvantage of this design is that subsequent improvements or renovations are considerably more difficult. In addition, only the bulk material behind the core seal is available as an abutment against the horizontally acting forces (the water pressure is directed against the dam) , because the water pressure acts on the seal. This means that dams with a surface seal need less embankment material.
The overflow ( flood relief system ) is usually built in masonry or concreted in earth dams and, if possible, founded on natural ground or even better on rock.
These barriers are often, but not exclusively, used for small pools on small rivers. Another possible application are large valley cross-sections with difficult subsoil. If, due to the subsoil conditions, such as a low compressive strength of the existing soil, only low soil pressures are possible, the dam construction is one of the best solutions for a dam because of its large contact area.
These walls are essentially made of masonry or concrete. The surface is sealed and the wall crown is attached. This type of dam can withstand the pressure of the water masses solely because of its weight.
Arch dam or vault dam
Arch dams are primarily used for very high and not very wide valleys. The wall is not level, but forms an arch that is stretched vertically and horizontally against the water. The pressure on the wall created by the water is diverted via the arch to the foundations on the side of the mountain. With this type of wall, the bond to the rock is particularly important. Arch dams are most commonly used in reservoirs in Switzerland and Austria, for example.
Arch weight wall
As a hybrid form between pure arch dams and gravity dams: some of the loads are carried by the arch effect, the rest by the cantilever effect of the wall. The necessary contact area is smaller than that of a gravity dam. The advantages compared to a gravity dam are a lower mass and compared to an arch dam, the lower load on the valley flanks and the lower effect of shrinkage of the concrete.
A pier dam is essentially a concrete dam with pillars that divert the forces into the ground, as well as with material-saving spaces.
Components of a dam
- Many dams have a pre- dam that dams a fore basin . The purpose of the pre-barrier is usually to keep foreign and turbid matter and sediments as far away as possible from the main barrier. In addition, a pre-barrier with permanent permanent backwater minimizes the not always aesthetically appearing dry bank zones in the reservoir root area .
- The overflow structure or the flood relief system leads large floods past the barrier structure without damage.
- The bottom outlet is used to regulate the water level, especially during floods, during construction work and when the dam is completely emptied.
- The service water extraction line extracts the water for turbine operation, drinking water extraction and / or underwater discharge during regular operation. It can be structurally connected to the bottom outlet, but is often designed as a separate line.
- The secondary barrier or the equalization basin below the main barrier compensates for irregular underwater discharges caused by turbine operation to generate peak electricity and ensures a continuous discharge into the underwater.
- At least one inflow and one underwater level document the hydrological situation and correct operation of the larger dams.
- Measuring and control devices for measuring and recording the water level, the deformation of the barrier structure, the seepage water and the weather.
Dam disasters can cause enormous damage. Therefore, high demands are placed on the projects, the construction and operation as well as the control of large dams. Several possible threats can lead to a hazardous situation:
- Behavioral anomaly of the structure (e.g. displacement, deformation) or its subsurface (e.g. change in seepage flow );
- Landslide or mass lintel ( landslide , glacial abort) in the storage space;
- extreme flood ;
- stronger earthquake ;
- Sabotage or military action.
The first three threats are usually recognized early so that measures can be taken before the population has to be evacuated (in the case of landslides, for example, the creation of drainage or the preventive lowering of the reservoir).
The security concepts usually prescribed by law include:
- constructive safety, which requires appropriate planning and implementation of the systems;
- surveillance, which requires the establishment of a strict surveillance organization;
- the emergency concept, which requires appropriate preparations in the event of danger.
Structural safety is guaranteed by the fact that the systems are planned and implemented in such a way that they can withstand all foreseeable loads and uses. When planning, all influences that can influence a dam must be taken into account. A distinction is made between permanent effects such as dead weight, changing effects such as water pressure or sediments , climatic effects and finally random effects such as floods or earthquakes.
In order to lower the water level if necessary or to empty a lake in the shortest possible time and, if necessary, also to keep it empty, appropriate structural precautions (bottom drain) must be taken. In addition, even when the basin is full, every dam must be able to safely discharge the flood via a flood relief system or be able to hold it back completely through a corresponding free space in the reservoir.
Regular and precise monitoring of the dam systems should make it possible to detect any impairment of their safety in good time. This is usually done through visual controls, direct measurements and functional tests of the movable closing and emptying devices. Monitoring includes:
- Flood relief: The flood relief is used for the controlled discharge of floods in the event that the storage tank is already full and a lot of rain falls in the catchment area of the storage tank. In the event of a flood, the water can drain away through openings in the crest of the dam, over which a bridge leads.
- Bottom drains: The bottom drains allow the storage tank to be emptied quickly in the event of danger.
- Monitoring by inspection: The visual controls not only allow the condition of the dam and the associated ancillary structures ( weathering of the materials, cracking, etc.) to be checked, but also those of the visible components of the foundations and the support of the flanks of the storage space. Around 70 percent of the special events at dams around the world are detected by visual controls.
- A comprehensive measuring system records how the dam reacts to the water pressure load and other external influences.
- Weather stations: Weather stations provide temperature and precipitation values. They are needed to assess the behavior of the lock. However, the weather values are also required in order to use the memory content optimally.
- Geodetic measurements: Geodetic measurements are carried out at least once a year. These are absolute position and height measurements.
- Water measurements : Measuring the seepage water is particularly important in the case of dams. Above all, the underground of barriers is never completely sealed. Leachate underground is part of the normal operation of dams. The seepage water allows conclusions to be drawn about changes in the dam body and in the dam subsurface. The water pressure in the foundation of barriers is of particular importance as the base water pressure in gravity walls . It acts on the dam body from the rock foundation. The stability of the barrier is guaranteed by sufficient drainage of the seepage water. The pressure on the bottom of the barrier is constantly measured with piezometers or manometers.
- Deformation measurements : The measurement of deformations is based on the physical principle that every structure deforms when it is loaded. Dams are stressed by water pressure and temperature fluctuations. The resulting deformations in dams are so small that they cannot be seen with the naked eye. All movements are recorded with the help of various special instruments. One measure, for example, is the so-called joint gap measurement .
- Extensometer measurement: With the extensometer measurement , the change in length of the dam is recorded in different directions of the dam.
- Plumb measurement: A plumb line inside the dam is used to measure whether the dam crest is shifting horizontally.
- Inclinometer measurement: The inclinometer measures possible changes in the angle of inclination of a dam.
- A comprehensive measuring system records how the dam reacts to the water pressure load and other external influences.
In addition, in many countries the creation of an emergency concept is required so that the residents below a dam can be informed and evacuated if necessary. In Switzerland, there are siren-based water alarm systems for the vicinity of the 62 dams with more than 2 million m³ of storage space . The near zone is the area that is flooded within two hours in the event of a sudden total breakdown of the system.
Safety rules in the individual countries
The monitoring takes place in Germany in coordination with the state supervisory authority of the respective federal state. Once a year there is a dam inspection. The supervisory authority visits the dam with the associated facilities with the operator. A safety report must be drawn up annually for each dam . The basis for the report is the leaflet 231 “Guideline Safety Report for Dams” published by the DVWK (German Association for Water Management and Cultivation). At longer intervals (approx. Every 10 years) the dams must be subjected to an in-depth inspection.
For each dam there is a "dam book" with the following components:
- Information and decisions from the planning and construction period
- Compilation of the application and approval documents
- Description of the entire system
- Description of the individual structures
- Operation and entertainment
- drawn illustration
In Austria, for assessing the safety of both newly constructed dams, and for the further approval of an existing plant, the storage tank Commission responsible. The owner is responsible for monitoring the safety of a dam, although independent safety reviews are also carried out by state bodies.
The construction of dams is associated with considerable ecological changes and damage to nature and the landscape. The natural flowing water regime is usually changed considerably.
The risks increase with the size of the dam. Several nations and international banks have come to the conclusion that the long-term effects of large dams cannot be foreseen. Some studies have not been published where they could be foreseen. This is evidenced in Germany by the non-publication of reports for a Hermes guarantee for the Ilisu dam .
There is a risk of silting up in rivers with heavy bed load . The Gezhouba Dam has lost its storage capacity by this effect after seven years of one-third.
The USA has declared that it will no longer build large dams because the ecological damage is too great. Billions of dollars are already being invested today to alleviate the effects of the existing dams. China, on the other hand, implemented the Three Gorges Dam despite warnings from many scientists and politicians about the consequences of the dam. There the main opponents - the population affected by resettlement, environmentalists, politicians and the military - were politically immobilized by various means. Reporting on the consequences that had already occurred, such as slopes and water pollution, was hindered.
In high mountains , especially with storage power plants that are not operated continuously, there is a risk of so-called surge water formation: When the power plant is switched off, the underwater is almost dry, while the river is in flood-like conditions when it is in operation. In addition to the ecological effects of such an operation, it is also conceivable that people will be seriously endangered by the sudden surge of water.
In addition to the risk of dam rupture, the risk of triggering earthquakes (“ reservoir induced seismicity ”) is suspected in some areas .
Dams that are subject to storage operation have seasonally changing water levels. The dry-falling bank areas often have little or no vegetation, consist of rubble or mud and are called "lunar landscapes" by some critics. In some dams, however, extremely rare plants have spread over precisely these areas and continue to require changing water levels in order to survive. These include, for example, strandling , deer jump and chickweed .
Number of dams
The ICOLD - International Commission for Large Dams counts 58,402 large dams, of which 23,842 in China, 9,265 in the USA and 5,102 in India as well as 307 in Germany.
The oldest still partially preserved dam in the world is the Sadd-el-Kafara in the Wadi el Garawi near Cairo, Egypt (according to various sources it was built between 2950 and 2500 BC).
A forerunner of today's dams was the Copper Age drinking water reservoir of Jawa in today's Jordan with an earth and stone dam, which is dated to the 4th millennium BC and which was built for irrigation and water supply.
Other important, large dam structures of antiquity are Nimrod's dam in Mesopotamia, which was built around 2000 BC. Was built south of Samarra to divert the Tigris, the dam of Ma'rib around 750 BC. In Yemen, the 31 m high Anfengtang dam from 591 BC. In China, the 34 m Paskanda Ulpotha dam in Sri Lanka from 460 BC, the 30 m high stone box dam at Gukow in China from 240 BC And the Roman dam of Subiaco, which was built around 60 AD and with 40 to 50 m by 1305 was the highest in the world.
The Romans built dams mainly in the dry peripheral areas of their empire. Their engineers introduced numerous innovative concepts into dam construction, including the first arched weight walls, arch dams , pier dams and multi-arched walls (see Roman dam ).
The oldest dams in Germany are:
- Middle Peacock Pond (1298)
- Gräfingründer pond (before 1310)
- Greifenbach reservoir (1396)
- Large gallows pond (1465)
- Felt pond (1485)
- Upper Großhartmannsdorfer Pond (1593)
- Upper Kiliansteich (1610)
- Devil's Pond (1696)
- Pear Tree Pond (1699)
- Wilhelmsthaler See (1712)
- Oderteich (1722)
The oldest drinking water reservoir in Germany is the Eschbachtalsperre in Remscheid (1891). Other dams followed their construction in quick succession (see list of dams in Germany ): by the end of 1914 around 37 dams had been completed.
In Austria , dams are mostly designed as hydropower plants and are operated by energy supply companies, since the (drinking) water supply has never been a problem. Smaller barriers were built in the late Middle Ages as part of the Holztrift , although considerable dimensions were later achieved with the Chorinsky Klause or the Prescenyklause . The Seeklause in Steeg from the 16th century was used to regulate the water level of Lake Hallstatt . In Vienna , the water supply was ensured by water pipes as early as the 16th century (see: Vienna water supply ). The water from the dam of the Wienerwaldsee , which was built between 1895 and 1898, was initially sold to the City of Vienna as industrial water. After appropriate modifications, drinking water was later taken from the lake, today the reservoir serves as a retention basin and for local recreation. The first dams for hydropower plants were built shortly after the First World War in Erlaufboden , Enzigerboden and at Spullersee , all for traction current .
In the 19th century, with the beginning of industrialization, the construction of numerous dams for electricity generation began in Switzerland. In the beginning, larger run-of-river power plants were built on the rivers of the Swiss Plateau, later storage plants followed in the Alpine region. Remarkable structures were built in the first half of the 20th century: the Montsalvens dam , the first arch dam in Europe, or the Schräh dam , the world's first system with a height of over 100 m. After the Second World War, the construction of dams experienced a great boom. Most of them were built between 1950 and 1970. During this period, dams with heights of over 200 m were built ( Grande Dixence , Mauvoisin , Contra , Luzzone ). Today, at the beginning of the 21st century, the period of intensive construction of dams is practically over. Systems for flood protection or for the production of artificial snow as well as debris collectors are still being built.
The security of the large and medium-sized dams (around 190 systems) is monitored by the federal government. Of this, 86 percent is used for the production of electrical energy, the rest primarily for the water supply (drinking water, irrigation) or to hold back floods, debris or avalanches. There are also several hundred smaller systems. A large part of this no longer serves a special purpose (e.g. because electricity production has ceased).
- List of reservoirs in Switzerland
- List of dams in Germany
- List of reservoirs in Austria
- List of dams in the world
- List of the largest reservoirs on earth
- List of the largest dams on earth
- List of places in Switzerland flooded by reservoirs
- List of dams and reservoirs in Namibia
- Peter Rißler: dam practice . 1st edition. R. Oldenbourg, Munich and Vienna 1998, ISBN 3-486-26428-1 .
- H. Bretschneider, K. Lecher, M. Schmidt: Pocket book of water management . 6th edition. Paul Parey, Hamburg / Berlin 1982, ISBN 3-490-19016-5 .
- Paul Ziegler: The dam construction together with a description of the dams implemented . Seydel, Berlin 1900 ( digitalis.uni-koeln.de ).
- Mathias Döring: Dams. In: Taschenbuch der Wasserwirtschaft. 9th edition. Springer Fachmedien, Wiesbaden 2015, ISBN 978-3-528-12580-6 .
- Benjamin Brendel: Dams . In: Networked, ways and spaces of the infrastructure (= Modern Regional . Volume 17 , no. 1 ). 2017 ( Moderne-regional.de ).
- Structurae: dams, dams and other retaining structures
- Types of dams ( Memento of April 4, 2008 in the Internet Archive )
- Construction of dams
- e-learning reservoir and electricity production
- Volker Bettzieche: 100 years of technical development in dam construction in Germany. (PDF). In: water management. Issue 1/2, 2010.
- Westphalian dams in the image archive of the LWL media center for Westphalia
- ↑ Peter Rißler: Dam practice. R. Oldenbourg Verlag, Munich 1999, p. 3, figure 1.1.
- ↑ DIN 4048, part 1 hydraulic engineering, terms. Beuth-Verlag, Berlin 1987, No. 1.2.
- ↑ Hans-Ulrich Sieber: What does the new DIN 19700 bring for the safety assessment of dam systems. ( Memento of the original from December 17, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Lecture at the German Dam Committee, 2004 (PDF).
- ↑ For example, in 1965 the lowland reservoir " Talsperre Spremberg " was built. It not only serves to protect the city of Cottbus from flooding and to supply water to nearby lignite power plants , but also to regulate the water level in the ecologically sensitive Spreewald . Source: Complicated renovation - conversion of the dam in Spremberg during ongoing operations. In: Märkische Oderzeitung . December 23, 2009, p. 9.
- ↑ Saxon Water Act (SächsWG) § 84
- ↑ Lower Saxony Water Act (NWG) § 86
- ↑ The text of this section comes largely from the message of the Swiss Federal Council on a federal law on dams, Federal Gazette 2006 6037 (PDF; 569 kB), p. 6040 ff.
- ↑ Reservoir Commission Ordinance 1985 (Federal Legal Information System), accessed on September 24, 2018.
- ↑ Reservoir Commission on the website of the Austrian Federal Ministry for Sustainability and Tourism, accessed on September 24, 2018.
- ↑ 12 theses on the safety of the large dams in Austria (Austrian Federal Ministry for Sustainability and Tourism), PDF, accessed on September 24, 2018.
- ↑ P. Talwani: On the Nature of Reservoir-Induced Seismicity. In: Pure Appl. Geophys. 150, 1997, pp. 473-492.
- ↑ Justus Teicke, Kathrin Baumann: dam operation for nature conservation. In: WasserWirtschaft. 04/2010. (www.talsperrenkomitee.de ( Memento of the original from March 13, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this note. , PDF; 227 kB ).
- ↑ Number of Dams by Country Members on the ICOLD website, accessed on July 17, 2016.
- ↑ Click on the triangle in the “Construction time” column - then the dams will be sorted chronologically.
- ↑ The above text comes from the message of the Swiss Federal Council on a federal law on dams, Federal Gazette 6037 of 2006 (PDF; 569 kB), p. 6041 (public domain text).