Development of flood risk and hazard maps at river Arachthos

Flood events are one of the most important natural phenomena with intense and extensive environmental, social and economic consequences not only in Greece but also worldwide. In the framework of this study we investigated the flood activity of Arachthos River (Epirus, Greece), downstream of hydroelectric dam of Pournari. The entire study area is very sensitive, particularly because the river crosses the urban area of Arta, which is located just after the dam. In this study, two hydraulic models, named HEC-RAS and quasi-2D LISFLOOD, were used to simulate flood events and map the resulting flooded areas, assuming in both cases steady flow conditions. HEC-RAS model is a 1 dimension hydraulic model, while LISFLOOD-FP, further to flood routing in main channel, incorporates methods for the propagation of flood waves across flood plains (quasi-2D analysis). Both models require as input elevation data in the form of Digital Elevation Model (DEM), which was initially processed in ArcGIS 10.0 suite. The same program was also used for the reproduction and presentation of simulation results in the form of flood risk maps. In this thesis, we studied 4 different flood scenarios, with different likely return period, by varying the management of weir system in Pournari dam. More specifically, further to real management scenario of flood event of 28-31/12/2005, we examined 3 alternative scenarios that result in different peak discharges. These scenarios can be attributed in the lag between the time of advent of peak inflow in the dam and the time that the weir system is starting to operate. This time lag has as a result the release of different discharge peaks from the weir. Further to that, hydraulic simulation was also conducted for the recent flood event of 1/2/2015 assuming an estimation of peak discharge, given that real data is not yet available. Finally, the hydraulic simulation results are composed and presented in the form of flood risk maps aligned with 2007/60/EC Directive for flood management in European Union.