A level is a gauge used to determine the water level in rivers , canals and other channels , in lakes and in the sea . In a broader sense, “level” also refers to the measuring point as a whole. The exact definition for Germany is laid down in the level regulation of the Federal / State Working Group on Water (LAWA) .
Colloquially , “level” is also incorrectly used as a synonym for the water level itself. At the gauge, however, only the level is measured from which the water level (water level for a representative section of the body of water) can be derived.
In hydrometry , the measuring point is also referred to as the "level". A distinction is made between levels at surface waters and groundwater measuring points . In shipping, a distinction is made between bridge level , inland level (rivers and lakes) and coastal level (sea).
Certain water levels also served as an orientation level for the national survey (e.g. Amsterdam level , Vienna zero , Kronstadt level , etc.). After the first height determination (e.g. by the normal height point in 1879 ), height information from the national survey is independent of water level fluctuations. Only the word level in the name reminds of the dependence on a water level.
In Europe, level measurements on rivers came about in the High Middle Ages , when the pre-industrial mill system developed and water abstraction required a legal basis. The performance of the increasingly widespread, more powerful medium- pitched water wheels was dependent on the water level and was prone to backwater in the underwater. Rights to water levels led to conflicts between the trades. One example is the mill pile , a pile to control the prescribed water level (target) of the mill water. The task of the mill piles has been replaced by hair markers that precisely mark the permitted storage height and are noted in the official water books .
The first regular and documented observations of water levels in flood protection in Germany go back to the end of the 18th century ( Elbe / Christian Gottlieb Pötsch (Meißen 1775, Dresden 1776), Erfelden / Rhein since July 1, 1797).
The level instruction drawn up by Eytelwein on February 13, 1810 is the first known service instruction on levels. It was updated and made more precise on September 14, 1874, but still only applied to Prussia. It was not until the level regulation of September 14, 1935 that water level monitoring in Germany was put on a uniform basis. It became binding for the states of Prussia, Anhalt, Bremen, Braunschweig, Hamburg, Lippe, Lübeck, Mecklenburg, Oldenburg, Saarland and Schaumburg-Lippe and from July 6, 1936 also for the southern German states of Baden, Bavaria, Hesse, Saxony, Thuringia and Württemberg introduced.
The water level of standing or flowing water is always measured in relation to zero level. It indicates the level of the water level (and should not be confused with the water depth).
Level zero point
The level uses the level zero point as a reference variable . The level zero point is set as far as possible below the lowest water level measured over a long period of time so that no negative values occur even when the water level is low.
In Germany, a level zero point is used uniformly in the coastal area, which is set at sea level minus 5 meters when it is set up. This is not identical to the nautical chart zero , which has been set to the lowest astronomical tide (LAT) locally since 2005.
The water level (water level) is the height of the water level directly on the gauge. It is generally given in centimeters (cm) and can be read directly from the staff or from the measuring device. The measuring range is usually a few meters. There are fixed abbreviations for important water levels, e.g. B .:
- MW: Mean water level is the average water level measured over a certain period of time (1 to 10 or more years).
- MNW: Mean low water level or mean low water is the mean low water level over a certain period of time.
- MHW: Mean high water level or Medium flood is the average high water level in a specific time period.
- NNW: Lowest Low Water Level or Lowest Low Water Level is the lowest water level ever measured.
- HHW: Highest flood level or Highest flood is the highest water level ever measured.
- HSW: Highest shipping water level is the highest water level at which shipping may be operated.
The water level is calculated from the height of the gauge zero point plus the water level above the gauge zero point:
- Water level above NHN = level zero above sea level NHN + water level above zero level
- In Germany, the zero point is given as normal height zero (NHN), in Austria as altitude above the Adriatic Sea (above sea level) and in Switzerland the zero point refers to the Repère Pierre de Niton in Lake Geneva.
The water depth is either measured directly or calculated using the water level and the water level plan (terrain model).
- The water depth of rivers and inland waterways is the difference between the water level above sea level and the river bed above sea level.
- The water depth of coastal waters is the difference between the seabed above sea level and the chart zero plus the tide height .
The headroom is the difference between the water level above sea level. NHN and lower edge of the bridge above NHN. In some places this difference is directly indicated by bridge levels. Vertical clearance is the minimum clearance between the mean flood and the lower edge of the bridge.
The gauge stations are generally integrated into the system of national coordinates , which means that precise geographical coordinates are also available. This measurement is usually carried out by local measurement of three fixed points that are assigned to the level.
Coast gauges are on the seashore, sea levels are further outside or float as a measuring buoy in the sea. Fixed levels have the same structure and function in the same way as the flow levels. Floating levels measure the water level georeferenced, e.g. B. with a Global Positioning System ( GPS ).
Measuring the tide
The tide , i.e. the changes in the water level at ebb and flow , is measured using coastal and sea levels. A forecast for the tide is calculated from the course of the measurement results ( hydrograph ). These forecasts are published in tide tables and tide calendars for the location of the gauge.
Measurement of height above sea level
Calculation of the water depth
For coastal navigation, the water depth is related to the sea chart zero . In waters with little tide (tide <30 cm) the chart zero corresponds to the mean water level in most countries. In tidal waters, the water depth is referred to LAT . In some countries, the water depth is related to other definitions of chart zero, for example to low spring water. All these averaged water levels are calculated from long-term observations of the water levels. See: Tide calculation .
There are internal levels on rivers, canals and lakes. They are used for shipping and hydrology and measure the current water level. The water level provides information about the water depth - depending on the location and shape of the subsoil and possibly in connection with the equivalent water level determined there . The change in the water level over time provides information about the expected navigability and a possible flood risk. In the case of rivers, each section of the river is assigned a reference level, the so-called “reference level”. Likewise with larger lakes.
High water marks
High water marks always relate to an associated reference level or the level measured there. The navigability by ships and their loading options depend on the water depth that can be derived from this . Directly dependent on the water level, the risk of flooding by flood . Navigability is limited due to the accelerated current and the changed lateral boundary of the river beds. In Germany, the limitation on inland waterways is determined by ordinances.
High water mark I
If the high water mark I is reached at the reference level, the first restrictions begin for the corresponding stretch of water. These vary from body of water to body of water and depend on the height of the bank (freeboard), the dam. or dyke height, on the technology of the ships, their size, speed, loading depth and wave form. The affected section can also be completely blocked.
High water mark II
If the high water mark II is exceeded at the reference level, the waterway is closed for all shipping with a few exceptions.
High water mark III
If the high water mark III (if present) is exceeded at the reference level, shipping is prohibited because the current speed then no longer allows safe maneuvering.
HSW = Highest shipping water level
This term was established by the Federal Ministry of Transport at the International Maritime Congress in Rome in 1953. The abbreviation HSW is often incorrectly translated as “highest navigable water level”. In Germany, even a decree of the BMV (July 14, 1959) could not eradicate the wrong translation and even specialist authorities often use this formulation to this day.
If a set mark (I, II or III) is reached or exceeded, shipping is stopped. The brand depends on the location. The restrictions are lifted again when a flood recedes (expires) and falls below the individual marks. For example, the high water mark I at the Karlsruhe-Maxau gauge is at a water level of 620 cm, the high water mark II at a water level of 750 cm, while the dams on the Rhine in the area are designed for a water level of around nine meters.
Importance for shipping
The levels are of great importance for shipping on rivers, lakes and seas. It serves as a guide level on waterways used by ships. The gauge is responsible for a specific stretch of water. In rivers with lock systems, the section is usually assigned to a specific lock.
The water levels at the reference level have an influence on the unloading depth of the ships, the clearance height of bridges and the limitation of shipping during floods. It is crucial for freight transport to be able to load as much as possible. When the water level is high, the amount of cargo and the number of containers stacked on top of each other is limited by the height of the bridge . When the water level is low, the amount charged is limited by the depth of the channel.
The problem in practice is that the water levels in each country are related to a different altitude horizon. The classification of the waterways is also different in each country, in Germany even differently east and west of the Elbe. In the EU, too, the classes still differ for historical reasons.
Importance in operational hydrology
On a river, the reliable recording and evaluation of water levels forms the basis for the hydrological description of the short-term and long-term changes in the overall situation of flow and water levels ( water balance ). It is used for the operation, maintenance and expansion and construction of the waterway , to control individual systems on the river, in particular the barrages with weir and hydropower station , shipping to determine the fairway conditions and the disposition of the unloading depth as well as the flood news service for the residents who living in threatened areas and for shipping.
For necessary flood warnings , automatic level measuring stations are increasingly being set up along rivers, which trigger an alarm when an adjustable warning threshold is reached . So-called call levels (level announcements) can be queried by anyone over the phone if required and indicate the current water level in centimeters or flow in cubic meters per second (m³ / s). For levels on German federal waterways, dial the area code and then 19429, for example for the Karlsruhe-Maxau gauge 0721 19429. The current water levels can also be found on the Internet (see web links).
Water level measurement technology
Locations, construction and testing
In Germany, the level regulation serves as a recommendation to the water management authorities for the construction of the systems as well as for their equipment, maintenance and operation. It is published by the state working group on water . A level is defined by a level staff and three height reference points, with the help of which the height of the level staff (level zero point) is obtained above sea level. Levels are to be attached to the water in such a way that the water level can still be measured even at the highest and lowest levels of the water. The water level zero point in Germany is measured and regularly checked by the Federal Waterways and Shipping Administration and the state survey offices. Due to the movement of the earth's crust, it changes the height of the level zero point continuously and due to the load differences at ebb and flow it rises and falls periodically by several millimeters.
The oldest and simplest form of measuring the water level is done with a level stick, which is attached to a quay wall, lock chamber or other wall. However, it can also be installed on the sloping terrain of a bank or ( dam ) embankment. A level rod is usually divided into decimetres with numbered black E-marks on a yellow background. A reading is usually possible with an accuracy of about one centimeter. In the case of inclined leveling staff, the division is stretched according to the incline.
A gauge system can consist of several level rods, also called level scales . If a level stick is flooded by the water, the reading is taken from the next, higher level stick. When changing from one level rod to the other, the readings are the same because the zero points are at the same height. According to the level regulation, these scales should overlap by at least 10 cm.
Today almost all level systems with a level stick have a write registration or save the measured values on site in a digital data collector. In the case of extreme flood events, the level rod is still an important measuring instrument today, when recordings are no longer possible due to failure of the energy supply or flooding of the level. Today, more and more of the most important water gauges are being equipped with redundant measuring and recording devices and data retrieval, so that a complete failure should no longer occur.
Such level rods can also be made makeshift. If necessary, they are erected in prominent places. These also show the classifications, but can possibly only be measured later.
The level clock shows the measured values with a pointer or two on a dial. With two pointers, the big one indicates the centimeters, the small one the meters of the level. Measurements are made by a float in a water level shaft that is connected to the water via a communicating tube . Such level meters are z. B. in Emmerich am Rhein , at the Cologne gauge or in Constance . The display itself is digital in many cases . In other cases, such as the historic water level house in Worms , it is analogous and resembles the face of a clock.
Nowadays the water level is measured at the water level with the help of floats , pressure probes , compressed air balances , radar and ultrasound devices . The measurements are recorded on level arcs, a tape recorder and / or in digital data collectors in the gauge house or boxes. Sometimes the water level is shown with a large digital display on the gauge house (see example image in the introduction above).
The water level of the body of water is measured in an adjacent shaft or by means of a pressure pipe. The height of the water level can be measured mechanically by a float with rope and counterweight (float level). At a pneumatic level, also called compressed air level, the water pressure is measured. A weight is pressed upwards by the water column in the connection shaft or the connection line (made of PVC). At the same time, the area above the weight is under pressure, which is generated by a compressor or compressed air cylinders . The pressure difference activates a mechanical recorder or controls an electronic measuring transducer, which records the water level. The measured values are converted into digital pulses by an angle encoder , so that the data from the data collector can be output to a central database directly by a laptop or via remote data transmission.
Mobile level measurement during floods
In order to quickly detect changes in the water level at particularly critical points during flooding, the level can be measured continuously using mobile radio sensors. This system, developed by the Federal Agency for Technical Relief , can also serve as a replacement if the fixed level has been washed away or exceeded.
Bridge gauges (also referred to as bridge clearance level in accordance with ELWIS ) are, predominantly on inland waterways, level bars attached in front of a bridge (e.g. vertically on the bridge piers), the skippers are not the water depth, but the free space, the clear clearance height under a bridge (i.e. , the distance between the respective water level and the lower edge of the bridge). For this purpose, they have an inverted scale, that is, the lowest point of the bridge construction (or any additions that may be present) within the marked passage width forms the zero point of the level. Bridge levels belong to the indicative shipping signs .
The animated picture shows the headroom at two different water levels (headroom 6 m and approx. 7 m). Passing through is recommended within the green and white signs, outside the red and white signs it is forbidden. With arch bridges , the clear passage width under the arch also changes depending on the water level. When the water level falls, the width of the fairway also decreases depending on the river profile.
In some cases, e.g. B. on sea waterways, other level constructions (level gauges, digital displays, etc.) are used as bridge gauges. Before going through, the skipper must decide, if necessary, whether his ship can still pass safely under the bridge, depending on the depth of immersion due to the load and / or fuel consumption. The fluctuations in height due to the run of waves must also be taken into account.
- List of national and international hydrographic and flood services - with links to water level values worldwide
Water and high water levels in Europe and the USA :
Water and flood levels in Germany :
- Hydrological information system of the Federal Waterways and Shipping Administration
- Flood control centers in Germany and neighboring countries
- ELWIS - water levels at levels relevant to shipping
- Federal Institute for Hydrology
- Federal Maritime and Hydrographic Agency (water level forecast)
- Project level - a project of the technical relief organization
- Flood news service Bavaria
- Flood forecast center Baden-Wuerttemberg
- Water levels in Hessen
- Internal level of the NLWKN (Lower Saxony)
- Online level data in North Rhine-Westphalia
- Level of the Ruhrverband
Further current water levels in Germany can be viewed at the water management authorities of the federal states .
Water levels in Lake Constance (transnational):
Danube water levels (transnational):
Water levels Austria :
- Water levels of the Danube and tributaries in Lower Austria
- Water levels of the Danube and tributaries in Upper Austria
Water levels in Switzerland :
Water levels in the Czech Republic :
- Catchment area of the March (de)
- Catchment area of the Oder (de)
- Vltava catchment area (de)
- Elbe catchment area (de)
- Eger catchment area (de)
- Czech rivers (en, de) Elbe, Moldau and others
- Definition of HSW
- Example of a digital level meter in Constance on Lake Constance
- Testing of mobile flood levels , technical aid organization.
- Archived copy ( memento of the original dated June 11, 2017 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.
- Shipping and bridge level - [WSV ] . November 7, 2004. Archived from the original on August 19, 2013. Shipping and bridge levels , Bremen Waterways and Shipping Authority.