Scenario of Flash Flood Caused by Hypothetical Failure of Mosul Dam in Iraq Using HEC-GeoRAS Model and GIS

Constructed on the Tigris River, Mosul dam is the most important hydraulic structure in Iraq, as well is the most dangerous dam in the world. Its geological foundation is unstable due to alternate and variable soluble strata formed from materials such as gypsum, anhydrite, marl and limestone. Consequently, it could collapse at any time and the lives of at least 1.5 million people could be at risk. The present paper investigate the flash-flood scenario due to a hypothetical disaster failure of Mosul dam using the Hydrologic Engineering Center's River Analysis System (HEC-RAS) in concert with HEC-GeoRAS and ArcGIS. The Landsat-OLI image and SRTM-V4.1 DEM data were exploited to digitize the river line, banks, path, and elevation. The cross sections over the river was created based on HEC-GeoRAS model to simulate the spreading of the dam-break flood after the flood-wave exits the narrow valley towards the city of Mosul and its neighbourhood. The 3D and spatial analysts in ArcGIS were applied to create water surface and the depth raster layer for the flash flood scenario. The results revealed that the flow depths can reach a 110 m by reference to bed of the river (or 32 m compared to the topographic surface), covering the Mosul city and extent situated at 75 km downstream of the Dam and sweeping an area about 30 km wide within few hours. The visual impact of this theoretical flood propagation was represented in 3D for land planning and a strategic plan preparation to protect and reduce the potential impact on human life, infrastructure, and environment in Mosul dam watersheds and adjacent regions.