Sensitivity analysis of Manning roughness coefficient of rivers in HEC-RAS model to determine flood zones (case study: Ker River- Fars province)

Subject Areas : civil and development planning

vahid sohrabi ¹ , Farshid Hashmipour Petkoi ² , Hamid Sheikhpur Shahi ³

1 - Geography and urban planning, Islamic Azad University of Larestan, Larestan, Iran
2 - Master's student in water engineering, Islamic Azad University, Larestan branch, Larestan, Iran
3 - Master's student in Marine Structures, Islamic Azad University, Research Sciences Unit, Tehran, Sirjan, Iran

Received: 2023-07-26 Accepted : 2023-09-22 Published : 2023-08-23

Keywords: Sensitivity analysis, HEC-RAS, Ker River, roughness coefficient,

Abstract :

Introduction: Rivers are one of the few natural phenomena that, despite the countless damages they have caused to humans since a long time ago, due to their special impact on human life and the formation of civilizations, humans have always been called to the lands along the river. In Iran, due to its large size, multiple climates, and temporal and spatial density of rains in most watersheds, huge floods have been witnessed in most regions of the country every year, many of which cause a lot of human and financial losses.Methodology: In this research, 10 km long stretches of the Ker River (downstream of the Chamriz Hydrometric Station) were selected, and after preparing the statistics of the maximum instantaneous discharge of the river in two states before and after the construction of the Molla Sadra Dam, the effect of the construction of the dam on the river flow Checked out. Then, taking into account the river discharge per discharge with a return period of 25 years for two situations before and after the construction of the dam, the permanent flow model of the mentioned river was prepared by HEC-RAS software and then compared with each other. In the following, based on discharge with a return period of 25 years after the construction of the dam, the Manning roughness coefficient was changed to 50% of the initial value and the HEC-RAS model was implemented again. The construction of the said dam has caused some parameters such as water level, water flow speed, water flow area, flow rate in the river and also the flood of its plains to decrease.Results: The results of the sensitivity analysis of some parameters in relation to Manning's roughness coefficient showed that with the decrease of Manning's roughness coefficient, some parameters such as water level and flow area also decrease and parameters such as water flow speed, river discharge, river discharge on the right bank and the left increases and vice versa.