Early Warning and Mapping for Flood Disasters

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    EARLY WARNING AND MAPPING FOR FLOOD DISASTERS

    D. Mioca, *, B. Nickersonb, E. MacGillivrayc, A. Mortonc, F. Antond, D. Frasera, P. Tang e, G. Lianga

    aDepartment of Geodesy and Geomatics Engineering, University of New Brunswick, Fredericton NB Canada E3B 5A3

    - (dmioc, fraser, c1g68)@unb.cabFaculty of Computer Science, University of New Brunswick, Fredericton NB Canada E3B 5A3 - bgn@unb.cacEmergency Measures Organization, Victoria Health Centre, 65 Brunswick Street, Fredericton NB Canada E3B 1G5 -

    (Ernest.MacGillivray, Andrew.Morton)@gnb.cadDepartment of Informatics and Mathematical Modeling, Technical University of Denmark, Denmark - fa@imm.dtu.dkeNew Brunswick Department of Environment, Marysville Place, Fredericton NB Canada E3B 5H1- Pat.Tang@gnb.ca

    KEY WORDS: Early Flood Warning; Flood Disasters; Web GIS; Flood Plain Delineation

    ABSTRACT:

    In this paper, we present the development of a Web GIS based system for early warning and mapping for flood disasters. To

    improve flood warning, we developed a decision support system for flood prediction and monitoring that integrates hydrologicalmodelling and GIS. We present the methodology for data integration, floodplain delineation, and online map interfaces. Our Web-based GIS model can dynamically display observed and predicted flood extents for decision makers and the general public. Theusers can access a Web-based GIS that models current flood events and displays satellite imagery and a digital elevation modelintegrated with the flood plain area. The system can show the flooding prediction based on the output from hydrological modelingfor the next 24 and 48 hours along the lower Saint John River Valley.

    * Corresponding author.

    1. INTRODUCTIONFloods are common natural disasters in the world. Each yearthey cause considerable damage to peoples lives and properties.In spring 1973, the lower Saint John River in the Frederictonarea (New Brunswick, Canada) experienced its worst ever

    recorded flooding, resulting in economic losses of $31.9 million,and leaving one person dead (Inland Waters Directorate, 1974).At the peak of the flood, private houses and public churcheswere flooded, and roads and bridges were damaged.

    Since 1973 other floods have left another three people dead andcaused more than $68.9 million in damage.

    The Saint John River Forecast System operated by theDepartment of Environment Hydrology Centre is monitoringand predicting flood events along the Saint John River. TheHydrology Centre team uses hydrologic modeling software topredict water levels for the next 24 and 48 hours along thelower Saint John River Valley by inputting climate data,

    weather forecast data, snow data, and flow data.

    However, the predicted water levels provided by this systemcannot satisfy the requirements of the decision support systemfor flood events. The system neither directly display the areasaffected by flooding, nor show the difference between twoflood events. Based on the water levels, it is hard for users todirectly determine which houses, roads, and structures will beaffected by the predicted flooding. To deal with this problem, itis necessary to visualize the output from hydrological modelingin a Geographic Information System (GIS). GIS has powerfultools that allow the predicted flood elevations to be displayed asa map showing the extent of the flood inundation. After theinterfaces for the visualization of the impact of flood events are

    designed, a computerised system is developed that predicts the

    extent of floods and dynamically displays near-real-time floodinformation for decision makers and the general public.

    Figure 1. The impact of flooding in Fredericton, NewBrunswick in Spring, 2008

    Figure 2. Flooding of St. John River in 2008

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    The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008

    In the past decades, hydraulic and hydrologic engineers havedeveloped many methods for delineating floodplain boundaries.Most of these methods are manual, tedious, and labour-intensive. With the advent of robust computer tools and highaccuracy Digital Terrain Model (DTM), automated floodplaindelineation is achievable. Recently, several managementsystems for floodplain delineation have been developed and

    applied in the flood event areas. These include floodplaindelineation using watershed Modeling System (WMS),(Reference Manual and Tutorial, 1998), Arc/Info MIKE11_GIS(Reference User Manual, 2004), and HEC-GeoRAS (Ackerman,2005). In this project, we used CARIS software to implementfloodplain delineation. CARIS (Computer Aided ResourceInformation System) develops and supports rigorous,technologically advanced geomatics software for managingspatial and non-spatial data. CARIS software supportsTriangulated Irregular Networks and offers advancedalgorithms for Digital Terrain models, such as interpolatingelevations for given coordinates. In the next sections, we willshow how CARIS can be integrated with hydrologicalmodelling to generate floodplain maps.

    4. FLOOD PREDICTION AND MONITORING SYSTEMThe design of the system allows near real-time imagery ofactual flood conditions to be overlaid on the base mapping andexisting imagery, as well as overlays indicating 100-year floodextents. Map layers of transportation networks, hydrographicfeatures, property boundaries, municipal infrastructure (e.g.power lines, natural gas lines) and contour lines can also bevisualized.

    Hydrologicmodellingsoftware(e.gDWOPER,FLDWAV)

    Hydrologicmodellingsoftware(e.gDWOPER,FLDWAV)

    Predicted waterlevel anduncertainty

    Predicted waterlevel anduncertainty

    CARISfloodmodeller, watersurface TINmodellingand visualization

    EMOserver runningCARISSpatialFusion Enterpriseweb mappingservice

    WebbrowserWebbrowser

    Bridge sensorobservations (images,water level) server

    Agent enginefor planningbest routes,optimal actions

    Figure 6. Conceptual model of flood prediction and monitoring

    system

    The final software products are integrated together withinCARIS software as shown on the Figure 6. Several provincialand research organisations in New Brunswick (University ofNew Brunswick, Emergency Measures Organization, NBDepartment of Environment, etc.) have been actively involvedin the project. University of New Brunswick participation wasin developing flood modelling software, additional bridgesensor observations and multi-agent engine for planning bestevacuation routes. In this project, CARIS GIS software wasused to implement floodplain delineation and online mapping.

    5. INTEGRATION OF HYDROLOGICAL MODELLINGAND GIS

    The implementation that integrates hydrological modelling,Digital Terrain Modelling, and GIS algorithm for floodplain

    delineation will be presented in the following section.

    Floodplain delineation requires a high precision ground surfaceDTM. Analysis of available datasets showed that there arerange and accuracy limitations among these datasets. It istherefore necessary to test and integrate these datasets in orderto obtain a high accuracy Digital Elevation Model data. For this

    research, the accuracy of provincial elevation data and the cityof Fredericton data were analyzed. High accuracy control pointscan be used to evaluate the accuracy of DTM data. Thisprocedure is implemented by using CARIS GIS tools. Firstly,CARIS software is used to generate the TIN model fromelevation data. Then using comparative surface analysis tool,the differences between the elevations of the control points andthe interpolated elevation of the corresponding points werecalculated. Finally, the statistic accuracy was obtained and thecontrol points were plotted on the map.

    As shown on Figures 7, 8 and 9, the most significant inputs forautomated floodplain delineation1 are the DTM (see Figure 8)and the water levels shown on Figure 7. The process considers

    the DTM and water levels at different locations to determine thedirection and extent of flow over a floodplain for a givenhydrologic event.

    Figure 7. Modelling of water level surface using cross sections.

    The floodplain depth dataset is the primary output of thisprocess. It indicates the high water mark and the depth of waterover the floodplain, and is generated by comparing the watersurface TIN with the ground surface DTM data. Based on this

    depth data, the floodplain extent and depth maps can begenerated. The intermediate parts of the process involve geo-referencing the water levels, extending the water levels to thefloodplain area, and creating a TIN of the water surface. CARISGIS allows users to create an irregular TIN or regular griddedDTM, to perform the comparison between two DTMs, tointerpolate contours using a DTM, and to display the DTMusing the CARIS 3D VIEWER program. These functions ormodules were used for development of the algorithm forfloodplain delineation.

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    Automated floodplain delineation is an excellent tool forproducing floodplain extent maps (Noman et al., 2001;Noman et al., 2003).

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    The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008

    Figure 8. DTM and the floodplain of the area

    Figure 9. Floodplain delineation process

    The CARIS software provides effective spatial analysis toolthat calculates floodplain delineation and facilitates themapping of flood events. As an example of floodplain

    delineat

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