Does the VMM forecast every flood in Flanders?
Flood forecasters primarily target (major) unnavigable waterways. The VMM does not forecast flooding originating in the sewer system, or floods on navigable waterways. For the latter we refer to the Hydrologic Information Centre.
How far into the future do the forecasts extend?
The forecasting system makes calculations up to two days in advance. The graphs on the website each time show a period of two days in the past and two days in the future. The colours green (basic mode, no flooding) - orange (non-critical floods) - red (critical floods) apply for a period up to 24 hours in the future. Precipitation forecasts up to ten days in advance are used by flood forecasters but can only be viewed by operators as part of the “early warning” system.
How often is the website updated?
The maps and graphs, taken directly from the models, are updated every 30 minutes. The detailed models of the Dender basin are updated on an hourly basis (do note that due to the complexity of the models calculations last up to one and a half hours). In exceptional circumstances this 15-minute or hourly webstream can be terminated by a decision by the first operator. News and interpretations by the operator are adjusted as soon as the status changes.
Why does the VMM show the forecasting results on a website?
Floods on unnavigable waterways can occur very quickly, in some cases even within one or two hours. In addition the status changes quickly during a flood and it is not simple to provide current and accurate information, especially if several basins are affected. That is why it was decided to make a portion of the forecasting results available on the Internet. In this the VMM follows a development whereby other services (e.g., the KNMI and ECWMF) also post online forecasts.
How reliable is the information?
Any forecast by definition includes inaccuracies compared to the measurements carried out subsequently. There is ample evidence, however, that better than average efforts are made in the area of telemetry transfer, offline models, real-time configuration, hardware, etc., in order to achieve state-of-the-art forecasting systems. It can be stated that the forecasting information provided is based on the best available technology in this field.
Measuring data also contains inaccuracies by definition. For example, the flow at very low stages is for the most part subject to errors but also at very high stages the problem occurs. In addition, a number of measuring stations are since a few years hampered by plant growth in the watercourse resulting in the measurements providing a distorted image. If the measurement data exceed established confidence limits, they are automatically removed from the forecasting systems input. Other errors (e.g., spikes within the confidence limits caused by maintenance activities) are corrected manually by the operator.
Can I contact VMM for further information?
For general information about flood forecasters, citizens should contact the VMM information desk during office hours (9 a.m. to 12.30 p.m. and 1.30 p.m. to 4.30 p.m.) on 053 72 64 45, fax 053 71 10 78 or send an e-mail to info@vmm.be.
Why do some basins provide a detailed image?
In addition to the hydrologic model, which covers all of Flanders (OBM-Centrale), in the Demer basin, the Yser basin, the Dijle basin and the Dender basin detailed hydraulic models are set up, respectively referred to as OBM-Demer, OBM-IJzer, OBM-Dijle and OBM-Dender. In the future the other hydrographic basins in Flanders will be dealt with one-by-one. Setting up high-quality models does take some time, so the other basins will follow in the next few years.