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Flood Forecasting and Warning Services in general

Content Table

General description

Flood Forecasting

An exact and early Flood Forecasting allows accordant early warning of persons concerned as much as the establishment of necessary measures (see Flood Protection, Evacuation and Rescue Plans). Therefore, it can make an important contribution to avoid damage. Flood Forecasting is in most cases based on extensive numerical modelling which is created with hydrological and hydraulic models of different complexities. Depending on the local situation and available database, different input data was used e.g.:

  • data of precipitation (current and forecasted)
  • information about snow-melt, ice
  • current water level at gauge stations in concerned water (river, lake, sea (tidal effects), groundwater)

Forecasting systems can be connected with control systems and systems for decision support. That enables running through scenarios with different measures and implementation of accordant controlling (e.g. weir controlling).
The following factors are taken into account:

Cross-national information is needed if the river concerns more countries.

Figure 1: Predicted sea water level- input data for the DSS Flooding (Hunze en Aa's)

Flood Warning

Flood Warning is based on evaluated information about flood danger in a river basin. It informs about the condition and the estimated development of the meteorological-  hydrologic situation, the water level, the chronological sequence of the flood and also about the control of embankments and other hydrologic plants and furthermore about relevant ice, snow and groundwater level situations. Flood Warnings contain general tendencies and as much as possible a forecast about the further development of flood danger. They are released as warning and all-clear. the flood all-clear contains information about the end of flood danger and about the abandoning of flood news and alert services for the river basin. (from).
Within the warnings, there is division into different alarm stages, for instance (saxon flood center):

  • Alarm stage 1: Bank-full stage, first overflows
  • Alarm stage 2: Flooding of agricultural and forest lands and isolated buildings; slight traffic disruption on roads; closure of individual roads required
  • Alarm stage 3: Flooding of parts of connected built-up zones, trunk roads and railway lines
  • Alarm stage 4: Flooding of larger built-up areas with very high damage to property an imminent danger to human and animal life.

Possible information paths for flood warning for persons concerned are:

  • SMS
  • e-mail
  • radio/television
  • newspaper
  • internet
  • fax

Case studies

Operational flood forecasting and flood risk management in Groningen (Netherlands)
It is described why the waterboard of Noorderzilvest (responsible for nothern part of the Dutch provinces of Drenthe and Groningen) requires a forescasting system and how it is implemented. The forecasting system is based on the Delft- FEWS software of Deltares coupled with the numerical SOBEK model. Model results are five-day forecasts of water level at about 30 locations. (see full text paper and poster)

Figure 1: Processes carried out in FEWS (Gooijer, van Heeringen)

DSS Flooding Waterschap Hunze en Aas (Netherlands)
Within the DSS for the Hunze en Aa's 3 days prognoses of rainfall, wind and sea water levels were used combined with water level measurements. With the help of a scenario editor , the effects of measures that can be carried out within the water system, can be simulated. (see project description at the topic DSS)

Flood forecasting by automated implementation of current and forecasted rainfall data into a runoff model (Germany)
The potential to improve flood simulation and forecasting by the use of predicted rainfall data based on radar measurements (virtual gauge) was investigated in two projects. Thus, water level in water bodies could be forecasted at neuralgic point, based on runoff simulation done by the model STORM. The accuracy of runoff simulated was improved, when STORM was fed with short-term (2h- forecast) precipitation data. (link)

Flood Warning Service Lower Saxony (Germany)
Lower Saxony Water Management, Coastal Defence and Nature Conversation Agency (Niedersächsischer Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz, NLWKN) provides a large net of levels in several surface waters. Based on these measures, floods can be predicted and population and shipping can be warned in time. In cooperation with other states adjacent to the river Elbe, water levels are published online and spread by mail. Receivers of the mail service are institutions, which take care of flood protection and are involved in measures in case of emergency.
A flood warning service is also important for farmers. The earlier a possible flood emergency is predicted the earlier precautions can be started. Therefore a mail- service (UE- Hochwassermeldung(at)LWK- was established. The Chamber receives the flood warning service sent by NLWKN and forwards it to interested farmers, who can apply for it. Information is spread, measures can be initiated if necessary, and the security for farmers in areas along river Elbe, which are endangered by flood, increases. link

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Related Titles from IWA Publishing

Water, Wastewater and Stormwater Infrastructure Management - Neil S. Grigg 
Publication Date: Jul 2012 - ISBN - 9781780400334

Flood Risk and Social Justice - Zoran Vojinovic and Michael B. Abbott 
Publication Date: Mar 2012 - ISBN - 9781843393870

Water Sensitive Cities - Carol Howe and Cynthia Mitchell
 Publication Date: Oct 2011 - ISBN - 9781843393641

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