Due to changes in time and space in the value of the coefficient n, the determination of the coefficient n becomes a very complex problem. ĭetermination of “ n” value presents an influential and creative task in the hydraulics of open channel flows. Several empirical formulas for the estimation of the value of n in practical problems have been proposed in the past. As an empirical parameter, the roughness coefficient (Manning’s n) includes the elements of roughness of channel surface, bed material, vegetation, channel alignment and irregularities, channel shape and size, stage and discharge, suspended sediment load and bed sediment loads, etc. Because of the complexities of hydraulic engineering, specific values for the empirical parameters, such as Manning’s coefficient n, are often uncertain. The physical parameters describe the physical properties of materials usually, they are constants while the empirical parameters are established on mathematical models. The parameters from models practiced in the engineering of hydraulics may be grouped into two groups: physical parameters and empirical parameters. Knowing Manning’s coefficient of roughness in open channels is of great importance in achieving any modelling that aims to study a variable of river variables such as flooding, sediment transport, and others. Among various hydraulic parameters, especially in hydraulic modelling, the roughness coefficient (or Manning’s coefficient) is an important parameter. In forecasting and warning of a flood, the river stage and discharge are considered as the variables. In predicting flood, the mapping and estimation of flood volume and various hydrodynamic models are developed and applied to several rivers with the aid of computers and numerical techniques. Results from this investigation showed that a value of Manning’s coefficient of 0.025 gave an acceptable agreement between observed and simulated values of water levels. Graphical and statistical approaches were used for model calibration and verification.
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The HEC-RAS model was adopted, calibrated, and validated in adopting two sets of observed water levels.
#Hec ras modeling software#
HEC-RAS software was the simulation tool used in this study.
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This study submits the results of the proposition of a hydraulic model in order to determine the roughness coefficient (Manning’s coefficient n) of the Tigris River along 3.5 km within the Maysan Governorate, south of Iraq. In understanding the hydraulic characteristics of river system flow, the hydraulic simulation models are essential tools.