Numerical flood modelling and simulation following the dambreak of Dicle (Tigris) dam and Kralkizi dam

Throughout history, humanity has at first built settlements of civilizations close to freshwater sources such as rivers and lakes to try and find solutions for various ways to supply the water they need. Owing to the development of technology, dams have been built to provide energy, irrigation, drinking water, and to protect from flooding. When they are built, they are positioned at a higher location than the altitude of the city in terms of operating costs and allowing the flow of water by gravity to reach the city centre. Dams built above the altitude of residential areas have also revealed some problems and risks associated with possible dam . The first question that comes to mind is; "how are the cities affected?" It is vital to find the answers to these questions and to guide the relevant authorities with the emergency action plans that would be prepared along with dam failure flood risk maps to minimize the loss of life and property in possible dambreak. The Kralkızı and Dicle (Tigris) dams built within the scope of the Southeastern Anatolia Project in the Euphrates-Tigris basin are selected as the study area in this research. The possible failure of Kralkızı Dam located in the Tigris-Euphrates Basin and at a higher location with an average altitude of 100 meters from the altitude of Diyarbakır city centre with a reservoir volume of 1,919,000,000 m3 , and Dicle (Tigris) Dam at a higher location with an average height of 40 meters from the altitude of the city centre with a reservoir volume of 595,000,000 m3 poses a risk. The Dicle Dam Reservoir, which begins just at the end of the downstream direction of the Kralkızı Dam, offers a work-site which can rarely be encountered and the TigrisEuphrates Rivers are of strategic importance as waters that cross the border. The fact that the dam reservoirs are adjacent causes the two Dam Reservoirs to be considered one reservoir. The Geographic Information System (GIS) Global Mapper and ArcGIS were used to investigate the topography of the work-site and to create base files for flood programs. GIS data is in a raster format with a pixel resolution of five meters by five meters. This resolution is fairly a good value for accurately reflecting the flood propagation. Nine models were created through the HEC-RAS and DHI MIKE flood software programs. Risk maps of the flood propagation in the centre of Diyarbakir were obtained as a result of the possible failure of the Kralkızı and Dicle (Tigris) dams by utilizing these models as input data. A hydro-graph of the failure was obtained with the model of destruction as a result of over-flow and piping of the Kralkızı dam. Consequently received hydro-graph was defined as the entry hydro-graph into the Dicle (Tigris) Dam Reservoir; the collapse was modelled as overflow and piping, and hydro-graphs were obtained as a result of their simulations. This hydrograph is used in determining the entry hydro-graph to the plain between the Dicle Dam and Diyarbakir city centre by using the software programs HEC-RAS and MIKE through performed one-dimensional and two-dimensional modelling, and possible risk maps were obtained. In the study, significant stability problems were encountered since the flow rates in the hydro-graph obtained as a result of the dam collapse reached relatively high values, and the frequency of cross-section was not within the desired range in one-dimensional models. When the cross-section intervals in the models are too frequent, the section arms overlapped and caused errors in calculation. When cross-section ranges were taken wider, the program gave a warning of insufficient cross-section ranges. We have foreseen that the programs are running one-dimensional in the riverbed section and two-dimensional in the terrain and concurrently running their simulation to be more suitable in terms of dam collapse. Generally, according to the created modelling, the floods caused by the collapse of the dam did not affect the settlement areas, notably the Old City Centre of Diyarbakir. Some small settlements on the riverbed and nearby areas were flooded. Since the valley narrows in the Ongözlü (Ten-eyed) Bridge Region, the current speed increased and reached higher values in the section where the bridge is located. It has been concluded that the effect of flooding on the Ongözlü (Ten-eyed) bridge is a matter that should be investigated.