Stream gauge

A level is a measuring instrument for determining the water level in rivers, canals and other clotting, in lakes and in the sea. In a broader sense, called " level" the measuring point as a whole.

Tide gauges is used as height zero point for the land surveying. For this, the variations in sea level but must be averaged over several decades.

• 5.1 high water marks

• 8.1 sites, construction and testing
• 8.2 staff gauge
• 8.3 Pegeluhr
• 8.4 Registrant measurement
• 8.5 Mobile level measurement at high water

Disambiguation

The word comes from niederdt level. level " measuring line " from the medieval Latin Pagella " bar " and is etymologically related to " coasting ", measuring a direction.

Colloquially " level" also used incorrectly as a synonym for the water level itself. At the level but the water level is measured, from which the water level can be derived ( water level for a representative section of the water body ).

In hydrographic the measuring point is referred to as " level". One differentiates between levels of surface water and groundwater monitoring wells. In shipping, a distinction is made between the bridge level, Internal level (rivers and lakes) and coastal level ( sea).

History

The measurement of water levels goes back a long time. Even the ancient Egyptians have the water level measured on the Nile, to use this information in the management of their fields.

In Europe level measurements came up of rivers in the High Middle Ages, when developed pre-industrial mill nature and required water withdrawal of a legal basis. Thus, the increasingly widespread, stronger mittelschlächtigen water wheels were in their performance of the flood height dependent and vulnerable to backflow under water. Rights to flood heights led to conflicts between the trades. One example is the Mühlpfahl, a pile for controlling the required storage level ( water level ) of the Mühlwassers. The task of Mühlpfähle was replaced by Haim brands that accurately mark the approved storage level and can be noted in the official water books.

The first regular and documented observations of water levels in flood protection in Germany go down to the end of the 18th century back ( Erfelden / Rh. Since July 1, 1797).

Previously served medium water levels in major rivers as a local height reference for the height measurement - about the level of Cologne (Rhein) or the Vienna zero ( Danube Canal ).

The text drafted by Eytelwein level instruction of 13 February 1810, the first known statement about service level. It was updated on September 14, 1874 and clarified, but was still only for Prussia. Only the level of provision from September 14, 1935 provided the water level observation in Germany on a consistent basis. She was, with shows for the countries of Prussia, Anhalt, Bremen, Brunswick, Hamburg, Lippe, Lübeck, Mecklenburg, Oldenburg, Saarland and Schaumburg-Lippe binding and from July 6, 1936 for the South German states of Baden, Bavaria, Hesse, Saxony Thuringia and Württemberg introduced.

Basics

The water level of a static or flowing water body is always measured in terms of level zero. He gives the level of the water table to ( and should not be confused with the water depth).

Tide Gauges

Tide gauges are at sea coasts, sea levels are further out than buoy or swim in the sea. Solid levels are built the same and work the same as the river level. Floating level measure the water level with a GPS with SAPOS correction.

Measurement of the Tide

The tide, so the water level changes in the ebb and flow is measured with coastal and marine levels. From the course of the measurement results ( hydrograph ) a prediction of the tide is calculated. These predictions are published in tide tables and tide table for the location of the level.

Measurement of the height above sea

The mean sea level - which means water - can be computed with centimeter accuracy for a place. For this purpose, the water level is measured continuously and the mean at a seaside level during several decades. Since the 19th century were thus obtained selected level - zero points as the reference height of the land surveying, such as the Amsterdam Level, the Russian Kronstadt level for France, the level Marseille, for Italy the level of Genoa, for Switzerland the Repère Pierre du Niton in Geneva and for Austria - Hungary, the level Trieste. As water levels can be converted only be measured relative to the level zero the values ​​in absolute values ​​of the respective reference altitude.

Calculation of water depth

The water depth is obtained for the coastal shipping on the chart datum. In tidenarmen waters ( Tide < 30cm) the chart datum, in most countries the mean water level. In tidal waters, the water depth is based on LAT. In some countries, the water depth is related to other definitions of the chart datum, such as the Spring low tide. All these averaged water levels are calculated from long-term observations of the water levels. See also: Tidal account.

Internal level

Internal controls are set on rivers, canals and lakes. They are used for waterways and hydrology.

High water marks

On a return ( drain) of a flood and below the individual brands, the restrictions are lifted. For example, the high-water mark I at Karlsruhe- Maxau 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 about nine meters.

Importance for shipping

For navigation on rivers, lakes and seas, the levels are of great importance. At waterways that are used by ships, it serves as a guideline level. The level system is responsible for a particular section of water. In rivers with lock installations, the portion is usually associated with a particular lock.

The water levels at the target level have influence on the draft for the vessels, the vertical clearance of bridges and the limit of navigation at high water. For freight transport, it is crucial to be able to load as much as possible. At high water level the charge amount and the number of stacked containers is limited by the bridge headroom. At low water level the charge amount is limited by the water depth of the fairway.

The problem in practice is that the water levels are related to a different height horizon in each country. The classification of waterways occurs differently in each country, in Germany even different whether east or west of the Elbe. The classes differ still historically and in the EU.

Importance in operational hydrology

On a river the reliable collection and analysis of water levels is the basis for the hydrological description of the short and long-term changes of the overall situation of flow and water levels ( water balance). It serves the operation of entertainment and the expansion and construction of the waterway, to control individual plants on the river, especially the barrages with weir and hydroelectric power plant, the shipping to determine the fairway conditions and the disposition of the loaded draft and flood news service for the residents who live in areas at risk, and for navigation.

For necessary flood warnings increasingly automatic level monitoring stations along rivers are set up, sound the alarm when reaching an adjustable warning threshold. So-called call level ( level announcement) can if necessary be queried by telephone from everyone and give the current water level in cm or Flow rate in m³ / s. For level of German federal waterways you choose to the area code and then the 19429, for example, the level Karlsruhe- Maxau 0721 19429th The current water levels can also be experienced on the internet (see links).

Technique of measuring water levels

Locations, construction and testing

In Germany, the level of provision serves as a recommendation to the water management authorities for the construction of facilities and for their equipment, maintenance and operation. It is published by the Regional Working Group on water. A level is defined by a staff gauge height and three fixed points, by which the height of the tide gauge ( level zero) is based on NHN. Levels are at waters to install so that the water level even at high and low of the water body is still measurable. The level zero is calibrated in Germany by the Water and Shipping Administration of the federal government and the state survey offices and checked regularly. The movement of the earth's crust, they changed the height of the level zero continuously and lifts the load differences at low tide and high tide, and he descends periodically by several millimeters.

Staff gauge

Inclined staff gauge on the Isar in Munich

The oldest and simplest form, to measure the water level, is done with a level bar, which is fixed to a quay wall, lock chamber or a different wall. But you can a bank or dam embankment also be mounted on the sloping ground. A staff gauge is divided eg with numbered black E- marks on yellow background dezimeterweise. Since the cross-beam of E are each two inches wide and two inches apart, on a reading of this measurement is accurately possible. For tilted tide gauges the division is stretched according to the inclination.

A level system may consist of several tide gauges, also called level squadrons consist. If a staff gauge is flooded by water, there is the reading at the next higher level bar. In the transition from one to the other staff gauge the readings are the same as the zero points are at the same height.

Today, almost all level systems with staff gauge and a write register. During extreme flood events, such as the Elbe flood in 2002, the Elbe flood of 2006 and the flood of Pentecost 1999, the staff gauge is also now a major measuring tool when recording may not be performed due to power failure or overload of the electrical level.

Such tide gauges may also be prepared makeshift. They are built in prominent locations, if necessary. These also have the divisions, but they may be measured later.

Pegeluhr

The water gauge shows the measured values ​​with a pointer on a dial. Is measured by a float level in a shaft, which is connected through a communicating tube to the water. Such clocks are level, for example in Emmerich am Rhein, Cologne or at the level in Konstanz. The display itself is digital in many cases. In other cases, such as the built in 1897 Pegeluhr in Ludwigshafen, it is similar and resembles the face of a clock. The water gauge is no longer used for many years.

Pegeluhr on the park island in Ludwigshafen

Level with Mainz Pegeluhr

Level tower of the St. Pauli landing bridges in Hamburg with display scale. The round dial displays in this case at the time.

Registrant measurement

Measured the water level at the level today with the help of floats, pressure probes, pneumatic scales, radar and ultrasonic devices. The measurements are registered at level arches, a strip chart recorder and / or digital data collectors in the level cottage. Sometimes the water level with a large digital display on the level cottage (example image above in the Introduction).

The water level of the water is measured in an adjacent bay. The height of the water level can be measured mechanically by a float with rope and counterweight. In a pneumatic level, also called air pressure level, the water pressure is measured. In this case, ( PVC ) is pressed by the water column in the connecting duct or the connecting pipe has a weight upward. At the same time is the area above the weight under pressure generated by a compressor or compressed air bottles. The difference in pressure actuates a mechanical recorder or controls an electronic transducer that records the water level. By means of a rotary encoder, the readings can be converted to digital pulses, so that the data can be read from the data collector through a laptop or via remote data transmission.

Mobile level measurement at high water

To quickly grasp the changes in water level at high tide in particularly critical areas, can be measured with mobile wireless sensors continuously the level. Developed by the Federal Agency for Technical Relief System can serve as replacements for weggespültem or fixed level is exceeded.

Bridge level

Bridge levels are before a bridge (eg perpendicular to the bridge abutments ) mounted tide gauges, the skippers the clear height under a bridge (that is, the distance between the water level and the bottom edge of the bridge ) Show. You have to an inverted scale, that is, the lowest point of the bridge structure (or any existing extensions ) within the marked passage width is the zero point of the level. Bridge level among the indicative navigational marks.

In the animated image headroom at two different water levels ( Headroom 6 m and about 7 m) is shown. Within the green and white signs the passage is recommended outside of the red- white characters, the passage is prohibited. In arch bridges varies depending on the water level, the clear passage width under the bridge arch. With falling water level also decreases depending on the flow profile and the width of the fairway.

In some cases, other constructions level ( level clocks, digital displays, etc. ) is used as a bridge level.

Featured passage and whose width

Bridge level in advance of a bridge - clear height 23 m

Example, with a vertical clearance of 7.5 m; within the marked passage width