On the Study of Geomorphic Evidence of Sirvan River Flood in order to Estimate the Maximum Flood Discharge, in Different Return Periods

Determining the characteristics of floods are considered important to plan and control them. According to geomorphological evidences of the river flow, Sirvan River, as one of the most significant rivers in the west of the country, has had some floods in the past. The present study aims at simulating and analyzing Sirvan River floods based on geomorphological evidence. As a matter of fact, long estimation would lead to predict the river behavior and flood appropriately, therefore it is necessary to search for possible estimations to do river planning vigilantly.
Materials and Topographic maps scale of 1: 1000, Total Station mapping camera, the application of GIS, HEC-RAS and research are the most important and practical materials and tools applied in the present study. The flood evidence was identified as a result of mapping and field surveys. Moreover, the metric measurements of the stratigraphy were drawn in the environment of drawing LAND software.
Determining the Manning roughness coefficient, the data were entered the environment of additional GEO-RAS from GIS environment to model the riverbed. The output was sent to the environment of HEC-RAS to present hydraulic simulation. Finally, the output was presented as transected and longitudinal sections.
The findings of positioning flood level with different return periods showed that the flood discharge increased for each longer return periods and there was an addition on the flood level in each sections. The profile of each section shows the increase and decrease of the flood regarding the other sections. In fact, as the section level increases, high-profile flooding decreases. The maximum instantaneous discharge of Sirvan River during a 48-year period reveals that the occurrence of large discharges is expected, therefore, Sirvan River can be counted as the flooding rivers.
The simulation of Sirvan River Valley floods was done applying hydraulic model HEC-RAS. Besides, the morphological flood evidence (stagnant water deposits) in paleo flood reconstruction was used to estimate the maximum flow discharge rate. As a matter of fact, statistical and experimental methods to estimate this river discharge and the adoption of wrong results by the civil engineers have had irreparable property and fatality damages. The investigations showed that using ancient Paleo indicator of PSI can help to estimate and analyze the maximum discharge in the river channel in the environment of HEC – RAS software.
It is not safe enough to rely on short-term statistics of hydrometric stations and experimental methods to estimate the floods’ discharge. Estimated discharge in different return periods shows that the occurrence of severe floods is expected. Applying geomorphological evidences of the flood provide more data for the systematic data and the basin of the rivers with no hydrometric stations. As a result, long estimation would lead to predict the river behavior and flood, therefore it is necessary to search for possible estimations to do river planning vigilantly.