Differences between Effective and Physical Roughness Parameter-A Headwater Mountain River Experiment

One-dimensional hydrodynamic models (HM) are widely used in the hydraulic modeling of rivers and channels. The result obtained with this type of model depends largely on correct estimation the roughness parameter. The value of the roughness parameter obtained through a HM calibration process differs from the one measured in the field. Hence, the objective of this research is focused on identifying the difference between physical and effective roughness for different morphologies present in Mountain Rivers. Physical roughness was indirectly measured with field data and Manning equation, while Effective roughness was found through GLUE experiments using water depth as validation data in one dimensional models in HEC RAS. Physical and effective roughness coefficients have shown differences depending on the morphology. In Cascade and Step-pool the physical roughness is higher than effective roughness, while in Plane-bed effective roughness is higher than physical roughness. The differences are attributed to the deviations that occur between the real conditions and the flow idealizations in an 1D-HD model. For any modelling application is important to research roughness values used previously and avoid formulations or tables which are based on field measurements.