The Rrelationship Between the LFH Index and the Flood Zones with Different Return Periods (Case study: Ghere_ Sou River)

LFH Index shows flooding probability at meanders using morphometry of river, whereas HEC-RAS model predict flooding extent for each buffers of rivers by hydrolic and topographic data . In this study we have tried to find a simple method to replace HEC -RAS model by making a relationship between these two methods of prediction. Hence, we defined range of natural levees during field observation by a GPS set and draw a plan of river on a topographic map of scale 1:2000 . Then, LFH index was calculated for 31 River bend. Finally, the flood zones having deferent returns times was identified by the HEC --RAS and HEC-GeoRAS extension and its association with various amounts LFH indices were evaluated using SPSS software . The results showed that there isn’t significant correlation between flood zones and LFH index values . Replacing flood zones by the natural levees distances used in LFH and consideration of other parameters fixed, LFH values separately for each period was calculated and its relationship with real LFH indices was tasted . Results showed that there is a highest correlation with the 2 year computational LFH and we can predict 2-year flood zone indirectly second degree polynomial regression model.