A GIS-Based Flood Forecasting System

1 The Flood management unit of the Flanders Environment Agency, or VlaamseMilieumaatschappij VMM has developed and deployed an advanced Flood forecastingsystem throughout Flanders that monitors more than 4,000 km of the region s water-ways. It is used for Flood prediction and much Jim BaumannA GIS-Based Flood Forecasting System IntroductionLocated in the Low Countries of northwesternEurope, Belgium (and particularly Flanders)has historically suffered from flooding. Someof this region is at or below sea level andcontains a dense network of rivers that incre-ase the potential for flooding during periodsof heavy rainfall and storm named, Flanders is derivedfrom the Proto-Germanic word flaumaz,which means overflow or flooding. Recordsindicate that major storm surges between thethirteenth and seventeenth centuries destroy-ed more than 100 coastal villages in the years, the Flemish government hasimplemented Flood control projects, inclu-ding a comprehensive dike and canal sys-tem, in an effort to protect the , as a result of massive floods in1998, when the Demer River overflowed itsbanks and caused severe damage, thegovernment began exploring methods offlood a Forecasting System We began building a simple forecastingsystem for the Demer River in 2002, saidKris Cauwenberghs, head of the floodmanagement unit of the Flanders Environ -ment Agency, or Vlaamse Milieu maat -schappij (VMM).

2 The System generated pre-dicted stream discharge hydrographsshowing the variation of water dischargeover time. The modeled Demer River isabout 100 km in length, and the hydro-graphs were only used for internal purposesat that then, the VMM has developed anddeployed an advanced Flood forecastingsystem throughout Flanders that monitorsmore than 4,000 km of the region s water-ways. To publish the Flood forecast on theweb, VMM used ArcGIS for Server Enter -prise Advanced, as well as ArcGIS ImageExtension for Server, ArcGIS Spatial Analystfor Server, and ArcGIS 3D Analyst forServer. This software stack is used tomanage, analyze, and serve the massiveamounts of data collected by the Flood fore-casting and deterministic forecastingTo fully comprehend the dynamics of thewaterways in Flanders, surveyors have spentthe past 15 years extensively mapping themH e l p i n g M i t i g a t e S t o r m D a m a g e i n B e l g i u m16 March 2016 Flooding exampleThe default home-page of : showing current Flood status at all monitoring sites in r t i c l eby creating cross sections of the rivers every 50 meters.

3 The data col-lected includes detailed information on the profile of the riverbed andriverbanks, as well as the dimensions of bridges, locks, water reser-voirs, and other infrastructure along the waterways. This data is alsoincluded in the Forecasting System for monitoring and Flood asses-sment measurements are taken every fifteen minutes and togetherwith meteorological forecasts, are used as input for hydrologicalmodels. The hydrological models in the Flood Forecasting systems areused to predict the volume of the water discharge during a specificperiod of time. The outputs from the hydrologic models are also usedto feed the VMM s hydrodynamic models. This data is seamlesslymerged with data from other Flemish organizations for advancedimpact analysis and then shared with those agencies responsible forwater management and emergency planning. Originally, we used determi-nistic Forecasting for our pre-dictions, said Cauwen early Flood modeling pro-cedure was based on analy-zing existing conditions andsingle meteorological fore-casts.

4 Today, the VMM usesensemble Forecasting . Thistype of Forecasting employs amethodology based on repe-ated random samplings ofwater levels, flows, and preci-pitation to produce hydrodyna-mic models for the predictionof potential flooding outcomes. Ensemble Forecasting allowsus to deliver Flood forecasts tendays in advance, and VMMcan now confidently publish itsreal-time Flood forecast mapsto keep its residents aware ofpotential danger, resultant Flood maps canbe used not only for evalu-ating the predicted maximumflood extent but also for deter-mining the impact of a poten-tial Flood , such as which hou-ses and streets will be floodedso that precautionary meas-ures can be identify Flood -prone areas,the VMM creates simulationsby combining its hydrodyna-mic models with a digital ele-vation model and the rivercross sections and relatedinfrastructure mapped by thesurveyors. These simulations mimic the physical characteristics of awaterway by imitating how water flows through a specified provides a comprehensive overview of the entire river and faci-litates a highly accurate prediction of the extent of flooding when ariver overflows its banks.

5 The model is calibrated using data collectedfrom the historical storms that have struck the region. Using the same hydrodynamic models, we can also produce floodhazard maps in an off-line mode for insurance risk purposes, saysCauwenberghs. Instead of the actual Flood extent, these maps showthe probability of flooding based upon statistical analysis and can beused for spatial planning purposes or insurance risk calculations. To explore the Flanders Environment Agency s Flood Forecasting System , visit 2016A (customizable) Local dashboard-page: showing forecasted hydrographs and Flood maps around Geraadsbergen including water-related tweets. Mapping portal-page: showing data, tools and mapping allowing a webbased editing of flooded buildings, Flood depths and floodcontours.