Determination of Flow Resistance Coefficient in Gravel Bed Rivers (Case Study: Babolroud River, Mazandaran)

Manning's coefficient is one of the main factors that lead to energy loss in channels and rivers which have a very important role in water level in cross-sections of rivers. There are several methods that suggested by various researchers for estimating Manning's coefficients which are mostly based on experimental tests. In river hydraulic, flow resistance or Manning's coefficient is changing because of bed mobility. In this case, a flow resistance formula cannot be used directly without any information about changes of flow resistance coefficient, in different situations of flow and sediment processes. Babolroud- River of mazandaran selected for this study. So, results of various empirical methods obtained to find out this coefficient using field survey and characterization of rivers such as cross-sections, soil materials of river bed and banks, then results compared with observed and simulated data of river flow. According to the obtained results, koven's method, which has the lowest relative error percentages of 6.17% and 3.46%, and also the lowest root mean square error of 2.7 and 3.2, respectively, in Pashakola and Quran Talar hydrometric stations, is suggested as the best method for estimating Manning's coefficient in this river. After kowen's method, Jarrett's method with relative error percentage of 10.11% and 5.41%, and also the root mean square error of 4.5 and 4.5, respectively, is chosen as the second method for determining Manning's coefficient in Pashakola and Quran Talar hydrometric stations.