MODELING WATER ELEVATION IN NATURAL RIVERS USING VARIABLE MANNING COEFFICIENTSiavash Mohammadi and Seyed Mahmood Kashefipour
Various parameters such as bed and bank materials, shape and irregularity of the section, vegetation, river meanders, plan of the river path and etc. affect the flow hydraulic resistance. In open channel hydraulics the effects of all these parameters are generally considered as the roughness coefficient. The Mannings equation is one of the most practical equations to flow resistance analysis, in which the surface roughness is defined by Manning coefficient. It is obvious a relatively good estimation of this coefficient can highly affect the accuracy of water surface elevation predictions in numerical models. Since many parameters are effective on the value of this coefficient, in this research study it was tried to define the roughness coefficient somehow that it be able to dynamically change with different river and hydraulic conditions. The collected data in Karun River for two periods were used as the case study. It is shown that the accuracy of model predictions for water surface elevations were improved more than 20% in error estimation in comparison with the corresponding results obtained for a constant roughness coefficient.
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