Estimation of the Manning’s Roughness Coefficient During Measurements in Rivers Type Coast, Mountain and Jungle, and its Comparative Versus Empirical Equations and Calibrated Values

The morphological characteristics of the sections belonging to coastal, mountain and jungle rivers are influenced by the type of material and configuration of the river bed, the geometry of the section and its hydraulic characteristics. The "n" Manning’s roughness coefficient is presented as one of the parameters necessary for the elaboration of hydraulic models that estimate the hydraulic behavior of a stretch of river. The present study aims to evaluate the Manning’s "n" roughness coefficients selected from Table 7 of the book Open Channels Hydraulics (Ven T. Chow, McGraw-Hill, 1994) according to the characteristics of the river beds identified during the field work carried out in 37 rivers distributed between the coast, mountains and jungle of southern Peru, which were compared with the equations of Garde & Raju (1978), Meyer-Peter-Muller (1948), Bray (1979) and Limerinos (1970) versus the values ​​obtained after performing the calibration of the hydraulic models by using the HEC-RAS software. The calibration of the hydraulic models for a determined section, was carried out with topography information of the river bed and measurements obtained in the field work such as flow, velocities and water stress, with which the correction of the Manning’s "n" coefficients used in the model, was made, whose calibrated values, in most cases, are within the ranges established by the bibliography of Ven T. Chow. The calibrated models are then used to estimate the hydraulic behavior under the influence of maximum flow rates. This study shows that the values ​​selected in the field, which take as a reference the information from Table 7 of the book Open Channels Hydraulics (Ven T. Chow, McGraw-Hill, 1994), represent a better approximation of the physical characteristics of the real river bed in comparison to the values ​​obtained from empirical formulas for the stretches of rivers evaluated.