The Flemish Environmental Agency VMM (Vlaamse Millieumaatschappij) has launched a flood forecasting website, based on Wallingford Software’s FloodWorks solution, which allows the public to access detailed information on current and forecast flood levels and rainfall.

The website has a live link to the FloodWorks models, which constantly receive new telemetry data from observations of precipitation, stages and flows, and the results of weather forecasting for up to the next two days.

Maps, graphics, tables and texts including an interpretation by hydrologists will help you to assess the flood risk in a particular area.

This is the second forecasting system that VMM has developed - five years ago it undertook a major modeling exercise for the Demer river basin. AMINAL, as the organization was known then, commissioned a flood forecasting system designed to give operational flood forecasters the information to provide fast and accurate flood warnings. This covered the key flooding areas of the 2275km2 basin, including the towns of Aarschot, Zichem and Diest.

VMM Assistant Director Kris Cauwenberghs explains: “We had large flood control reservoirs ahead of the cities and wanted more information, data that could tell us what would happen when these were full.”

AMINAL has created two complex hydraulic models of the 300 km of watercourses, which included real-time data from telemetry such as the position of gates along the watercourses. “We were quite surprised - even now, after 100,000 simulations the system is still running. We are very happy, it is a very stable solution so we have planned to continue with our other regions.”

The difference is that the current ambitious programme is designed to make all of the information available to the public on the VMM website. Flanders has 11 basins, and VMM acknowledges that it will take a great deal of funding and time to cover the entire area - the organization anticipates a full seven years for completion.

“Because it will take so long we started with a simplified forecasting system last year, which was just the hydrology and not hydraulic models. It was still very complex - we input radar rainfall data from the three Belgian radar systems and calibrated it in real time with the rain gauge data. There are always multiple inputs - you need good inputs.”

The website now has publicly accessible models for the OBM-Dender and OBM-Centrale regions (hydrological forecasts for the Flanders region and hydraulic forecasting for the Dender basin). Clicking on an area brings up topographic maps, with full hydraulic data so that the areas at risk of flooding can be identified.

The modeling is extremely complex - for the Dender basin alone there are seven hydraulic models of watercourses, which include not only cross-sections of spill units, but also floodplain sections and gate information.  The seven models contain 13,000 nodes including spills, breaches, pumps, weirs, storage areas and flood compartments.

The original models utilized FloodWorks 3.0 running on a clustered server. Two hydraulic models enable forecasts of water levels in selected areas of the Demer valley, with a fully automatic 24/7 facility supervised by operators showing probable areas of flooding. Since its inception in January 2003, the original model has generated over 115,000 continuous forecasts.

The new models have been running on FloodWorks 6.0, still on a clustered server, since June 2007. These also generate hydrological forecasts rather than flood maps, forecasting the zones and times of regional and local flooding can occur in Flanders. The predictions are based on passing thresholds for rainfall, water levels and unit discharge levels in litres/sec/hectare, with alarm modes both for basins and sub-catchments and real-time updating from telemetry at numerous critical points along the areas’ river courses.

The system interfaces with radar rainfall information from Hyrad and hydrometric data from Wiski. There are 140 gauged sub-catchments of areas between 200ha and 800km2, modeled by hydrological PDM boundary in InfoWorks RS.

The hydrological model’s inputs include rainfall data from local rain gauges and evaporation data, from which predictions on flows, water levels and soil moisture deficits are provided to the warning system, and for local forecasts.

48-hour hindcasts and forecasts are provided, with area rainfall based on data from the five closest OTT rain gauges and basin rainfall levels based on data from all rain gauges. Radar rainfall information is based on either a recalibrated or uncalibrated actual image. Radar forecast data comes from the Nimrod NWP model, and long-term forecasts from the ECMWF EPS rainfall forecasts.

Evaporation is similarly hindcast and forecast using data from both the nearest and second-nearest meteorological stations and minimum and maximum temperature readings to calculate Hargreaves evaporation levels - forecasts use predicted temperatures to calculate this level.

Local flooding is broken down into 1345 region-wide subcatchments of between 55 and 7800ha for predictions using the Simplified Runoff Model boundaries in InfoWorks RS.

The long-term plan is to extend the amount of detail in the Dender basin to every basin and every river where flooding is a potential hazard. At the moment 10% of the watercourses in the region are online, with the rest following. “It will take time and it is not a project that you should do fast,” Mr Cauwenberghs explains. “It takes a lot of effort, but it is quite stable.”