Investigation of Effective Factors Role on 18 March 2019 Floods of the Kiakola in Mazandaran Province by HEC-RAS Model

Introduction and Goal
Heavy rainfall events in short terms makes a plenty of precipitation volume that commonly causes severe problems in human community, flora and fauna. The Simorgh city was damaged financially by the floods on March 18, 2019. Hydraulic simulation from upstream to downstream of the Kiakola town causes to find the inundation factors and prevent to repeat of such events. Purpose of this research is a simulation of 18 March 2019 floods in the Telar River in Kiakola town of HEC-RAS model and determining effective factor’s role in this flood event to present some countermeasures for preventing of happening such inundation in this region.
 Materials and Methods
In this research, 10 km of the Telar River in the west of Simorgh city was studied. In this area, there were bridges, Najjarkola, Mollakola and Borjkheil, all of their geometric dimensions of bridges with geographic coordinates, see level elevations and distances of 26 cross sections which surveyed by theodolite and GPS multi frequency device. The hydrograph of the Telar River was simulated by the HEC-RAS Model in 18 March 2019. To obtain the return period of 18 March 2019 flood, 65 years' time series of the Telar River discharge in the Kiakola Hydrometric station was analyzed by Easy Fit. The river bed was determined by 25 years return period flood and river limits was determined by DLSRS method which mentioned in determination of quantitative limits of river instruction.
Results and Discussion
Frequency distribution analysis was done by Easy Fit software on historical discharge of the Kiakola hydrometric station showed that return period of peak discharge on 18 March 2019 hydrograph was equal to 24 years. Simulation of 18 March 2019 hydrograph on study reach indicated that all cross sections of the river and all three bridges had enough capacity to pass the flow and no damage was done to the river bed in the studied path, but a large part of the 20-m privacy strip of two the side of the river was damaged by planting fruitful trees, which, of course, had no effect on the occurrence of flooding caused by the flood of 18 March 2019 in Simorgh city.
Conclusion and Suggestions
The flooding of the city of Kiakola and the surrounding villages was not due to the inappropriate geometric dimensions of the bridge, but because the opening of the bridge was blocked with the trunks and branches of trees transported from the upstream of the watershed to the bridge site, which, like a significant number of natural disasters, confirms neglect It is related to watershed operations in watersheds of natural resources. Preventing the change of use of forest and rangeland in mountain watersheds and building crossing structures to collect floating and submerged bodies in upstream watersheds are measures that minimize the possibility of repeating such consequences.