Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Alarm
Status or condition of the water system in which one or more alarm thresholds are reached. For flooding and tides, an alarm is defined as a condition that requires maximum vigilance and that may give rise to critical flooding. Measurement or forecast points in alarm status are coloured red.
Alert
Status or condition of the water system where one or more alert thresholds are reached. For flooding and tides, an alert is defined as a condition that requires particularly heightened vigilance and that may give rise to non-critical flooding. Measurement or forecast points in alert status are coloured orange.
Area precipitation
The area precipitation is a precipitation series that is generated for a given (measurement) point in a watercourse. It approximates as closely as possible the total precipitation in the area that drains to that point in the watercourse. The area precipitation is calculated on the basis of radar images and pluviometers.

C

Civil engineering structure A civil engineering structure on a watercourse is any man-made construction such as e.g. a weir, lock, gate or pump.

D

Dashboard
A dashboard of waterinfo.vlaanderen.be is a web page where you, as a professional user, can assemble modules that are of interest to you. The graphs and zoomed-in" maps for your area are thus displayed on a single screen for fast and easy access. You will have access to five dashboards to which you can directly add other modules of interest via the icon at the top right of the module.

F

Flowmeter
A flowmeter is a measuring instrument that transmits sound waves through the water to measure the flow velocity of the water, expressed in m/s. Together with a measured wet upper surface or cross section of the watercourse (m²), this results in a flow, expressed in m³/s. The flow velocity of the water can be measured in various ways. On the one hand, there are the so-called runtime meters, which measure the time difference between two sound waves transmitted and received on opposite banks. The difference in runtime is an indication of the flow velocity of the water. On the other hand, there are Doppler flow velocity meters, which measure the flow velocity on the basis of the frequency shift between a transmitted high-frequency sound wave and the sound wave reflected back by particles (moving at the speed of the water).
Forecast point
Point where water level forecasts based on a hydraulic model are shown. In this case, measurements are usually not available.
Freeboard
A freeboard indicates the margin before the dykes of navigable watercourses are flooded. It is the distance between the water level and the dyke. For the short-term forecasts under the flood and tide themes, freeboards appear on the map if the dykes of the watercourse change colour. Depending on the margin and the severity of the situation, they are coloured green, yellow or red for normal situation, heightened water level and flooding, respectively.

H

HIC
The Hydrological Information Centre belongs to the Hydraulics Research Laboratory and falls under the Department of Mobility and Public Works of the Flemish Government. The HIC has measurement infrastructure and forecasting systems for the navigable watercourses in Flanders.
Hydraulic model
A hydraulic model contains all topographic data of a watercourse and its valley, as well as of the civil engineering structures on the watercourse, such as spans, bridges, retention basins, weirs, etc. The flow series from hydrological models are fed into this model. The hydraulic model calculates the progression of the flow in the watercourse and in the valley, as well as the associated water levels and flow velocities. The hydraulic model uses this information to generate flood maps.
Hydraulics Research Laboratory
The Hydraulics Research Laboratory is a department of the Technical Support Services of the Mobility and Public Works department of the Flemish Government. An expertise centre, it carries out research into the effects of water in motion, and is one of the partners of waterinfo.vlaanderen.be.
Hydrographic basins
Flanders has 11 hydrographic basins or catchment areas. From west to east, these are the basins of the IJzer, the Bruges Polders, the Leie, the Ghent Canals, the Upper Scheldt, the Dender, the Lower Scheldt, the Dijle and Zenne, the Nete, the Demer and the Meuse.
Hydrological model
A hydrological model or rainfall-runoff model is a model that describes the relationship between rainfall and evoptranspiration in a catchment area, on the one hand, and the runoff to the watercourse, on the other hand. The hydrological model is tested against a measured flow series and subsequently used to convert rainfall series into flow series.

I

Infrastructure meter
Collective name for measuring stations at man-made facilities on watercourses, such as valve weirs, gates and pumping stations.

L

Long-term forecast
Long-term forecasts are calculated up to 10 days ahead for a selection of locations on non-navigable watercourses. These graphs, too, show a band of forecasts that indicate the reliability of the forecast. The wider the band, i.e. the further the forecasts are from each other, the lower the reliability. Between April and October, there are also long-term drought forecasts, which can be found under this theme.
Limnigraph
A limnigraph is an instrument that measures and records the water level in a river. Using flow velocity measurements, a QH relationship, i.e. a relationship between water level and flow, is established at frequent intervals at the level of the limnigraph. This QH relationship allows the water level time series to be converted to a flow time series at the level of the limnigraph. Water levels can also be measured using acoustic sensors or pressure sensors.

M

MDK
The Maritime and Coastal Services Agency (MDK) ensures safe and smooth navigation from and to the Flemish ports. MDK is responsible for protecting the Flemish coast from floods and promotes an integrated and sustainable management of the coastal area. The Oceanographic Meteorological Station (OMS) is part of MDK and compiles daily sea level forecasts at a number of strategic locations. MDK is one of the five partners of waterinfo.vlaanderen.be.

N

Non-navigable watercourses
The watercourses in Flanders are subdivided into a number of categories. First, there are the navigable watercourses and canals managed by entities within the Department of Mobility and Public Works (MOW) policy area. Second, there are the non-navigable watercourses, which are subdivided into categories 1, 2 and 3. The Operational Water Management department of the Flemish Environmental Agency manages the category 1 Flemish non-navigable watercourses. The category 2 watercourses are managed by the Provinces, and the category 3 watercourses by the municipalities.

O

Operator / Officer on-duty
The forecasts on waterinfo.vlaanderen.be are evaluated, interpreted and explained in waterinfo reports by various individuals. At VMM, an operator performs this task for the non-navigable watercourses. The operator is automatically notified by the systems in the event of a transition to an alert or alarm situation. He/she decides whether a flood forecast is of such a nature that the emergency services and the authorities need to be warned. At HIC, the officer on-duty performs this role for the navigable watercourses. He/she notifies the operators of the navigable watercourses (NV W&Z, NV De Scheepvaart) in the event of imminent flooding.

P

Pluviometer
A pluviometer or rain gauge is an instrument that measures precipitation. The pluviometer typically includes a logger that records the rain distribution in time. The reference rain gauges used by VMM use a weighing scale instead of the older tilting bucket system. This is a more expensive but also more accurate measuring method.
Percentile
A percentile of a given parameter indicates the percentage of time during which that parameter remains below a specified value. If the 25 percentile of the water level at a given location is 8.0 m TAW, this means that the water level is less than 8.0 m TAW for a quarter of the time. You can call up a figure with associated table of the distribution of certain parameters for various measuring stations. These figures are available both for each measurement year and for the entire measurement period.
Point rainfall
Point rainfall is recorded by a pluviometer or rain gauge. Several tens of these pluviometers distributed across Flanders transmit new data every 30 minutes.
Pre-alert
Status or condition of the water system in which one or more pre-alert thresholds are reached. For flooding or tides, a pre-alert is defined as a situation of heightened vigilance. On the navigable watercourses, no flooding is forecast in the event of a pre-alert; on the non-navigable watercourses, non-critical flooding is forecast in event of a pre-alert. Measurement or forecast points in pre-alert status are coloured yellow.

R

Rainfall deficit
The rainfall deficit is an indicator of the amount of rainfall that is lacking for optimal crop growth. It is obtained by calculating the difference between the calculated reference crop evaporation (potential evapotranspiration) and the amount of rainfall. This difference is totalled daily from 1 April to 30 September. A negative number indicates a rainfall surplus, a positive number a rainfall decifit.
Rainfall radar data
These are rainfall time series originating from rainfall radar instruments. They are obtained using a radar antenna that sends out a pulse-shaped radio signal, which is partly reflected by precipitation. The position of precipitation areas can be derived from the direction of the antenna and from the time that elapses between transmission of the pulse and reception of the echoes.
Return period
A return period indicates the probability of occurrence of an event. It is usually expressed in years. An event with a return period of 10 years occurs on average once every 10 years. The probability of occurrence of an event with a return period of 5 years is two times that of the probability of an event with a return period of 10 years.

S

Second General Water Level (Tweede Algemene Waterpassing, TAW)
The second general water level is a reference for height measurements in Belgium and refers to height indications above sea level. All height values in the measurements of the watercourses and their valleys and all water levels are expressed according to this reference system. The use of this reference system is indicated by the notation "m TAW".
Short-term forecast
Computer models use measurements and weather forecasts to calculate water levels and flows in the watercourses up to 48 hours ahead. These forecast levels and flows can be viewed under the “flooding” and “tides” themes in the graphs on waterinfo.vlaanderen.be, which are generated around the clock. For short-term forecasts on the navigable watercourses, the uncertainty of the forecast is also indicated. The map for these themes shows flood maps and freeboard maps. On flood maps, the blue areas indicate how far the flooding is expected to extend. Freeboard maps use the changing colours of the dykes of navigable watercourses to indicate the distance between the forecast water level and the dyke. Under the theme “rainfall”, you can find short-term rainfall forecasts up to 48 hours ahead.

Status

The status of a measurement or forecast point indicates the condition of the water system, with a distinction being made between normal, pre-alert, alert and alarm. Each status is assigned a colour (green, yellow, orange, red). The thresholds for transition to another status were pre-defined for measurement points and forecast points, on the navigable and non-navigable watercourses, and for the various themes (flooding, tides, rainfall, drought). For the theme 'flooding' the meanings of the terms are given below:

Status	Colour	Description
Normal	Green	No flooding
Pre-alert	Yellow	Heightened vigilance, no flooding
Alert	Orange	Particularly heightened vigilance, non-critical flooding possible
Alarm	Red	Maximum vigilance, critical flooding possible

STF
On the graphs of the forecasts, the abbreviation 'STV' stands for the start time of the forecast (starttijd van de voorspelling). This is the time at which the computer model started computing, using the most recent measurements and rainfall forecasts available at that time.

U

Uncertainty bands
Uncertainty bands provide an indication of the probability of the forecasts. They appear in the graphs of the short-term forecasts for navigable watercourses and the graphs of the long-term forecasts for non-navigable watercourses. Uncertainty bands are calculated on the basis of various possible rainfall forecasts that predict more or less rainfall. The wider the band, i.e. the further the forecasts are from each other, the greater the uncertainty.

V

VMM
The Flemish Environmental Agency (VMM) manages and monitors category 1 non-navigable watercourses using measuring infrastructure and forecasting systems. VMM is one of the five partners of waterinfo.vlaanderen.be.

W

Water assessment
The water assessment evaluates whether a project (the building of a home, the construction of a street) will cause harmful effects to the environment as a result of a change in the condition of the surface water, the groundwater or the water-dependent nature of the project.
Water level gauge
A water level gauge or limnigraph is an instrument that measures and records the water level in a river. Using flow velocity measurements, a QH relationship, i.e. a relationship between water level and flow, is established at frequent intervals at the level of the limnigraph. This QH relationship allows the water level time series to be converted into a flow time series at the level of the limnigraph.