Flood analysis of Trabzon Değirmendere basin using geographic information systems and a hydraulic model

Flood disaster is one of the most important meteorological hazards from theviewpoint of damages on humans. However, unplanned urbanization andinsufficiency of protections are leading factors to the flood disasters. Modelingof the floods and determination of the areal extent of inundated areas areimportant contributions to solution of the problem. Geographic InformationSystem (GIS) application which can operate together with hydraulic models isone of the most important tools that could be used for modeling of the floods.Trabzon Değirmendere Basin located in Eastern Black Sea Region where themaximum precipitation in the country is experienced, is selected as the studyarea. The heavy rainfall and the large size of basin (1054 km2) cause high peakflood values. In this study, terrain modeling and determination of floodplainareas have been done the GIS software of ArcGIS 9.3, and hydraulic analysishas been realized by using Hydrologic Engineering Centers River AnalysisSystem (HEC-RAS) 4.0. Especially in Maçka county; it is determined that manyplaces would be affected during the probable maximum flood period due tosettlements on the banks of the river, and the decreasing of channel crosssection by the existing bridges. The missing data of the special map of 1/2000scale, prepared for defining the geomorphology and the settlements of the studyarea, used as input for modeling have been completed by field observations and includedinto the map by digitizing. Thus, 3D terrain model of the studiedsection has been created by ArcGIS. All the topographic data obtained, havebeen transferred to the HEC-RAS which makes hydraulic analysis using HECGeoRASmodule. The computed discharge values of different recurrenceintervals were included into the hydraulic model, and the water levelscorresponding to the same recurrence intervals have been determined, andflood risk maps have been prepared by transferring the results to ArcGIS usingHEC-GeoRAS. The structural and non-structural solutions have been proposedaccording to the areal distribution of the inundated settlements.