Hydraulic Modeling of River Discharge Subjected to Change in Riverbed Morphology

In natural channels such as rivers, the flow behavior is highly complicated phenomenon due to unsteady and nonuniform flow. Hydraulic modeling is essential for the study of characteristics of unsteady flow in rivers. Changes in riverbed morphology influence the increase in depth of flow in rivers. In the present study, the roughness coefficient is varied to match the natural condition. The objective of the paper is to study the effect of the change in riverbed morphology on the river discharge using a hydraulic model. The study is carried out using the Hydrologic Engineering Center—River Analysis System (HEC-RAS). A river length of 12 km of the  Nethravathi river regime, Karnataka from  Uppinangadi to Bantwal is considered for the study. Daily river stage and discharge data are collected from Central Water Commission (CWC) gaged at Bantwal station. GIS interface of HEC-GeoRAS is also used to extract the cross section, bed slope, and length of the river channel from Digital Elevation Model (DEM) data of resolution 30 m. The cross sections are represented for each kilometer length of the river. Since accurate data is unavailable in the study area, cross sections are simplified. HEC-RAS model was used for the simulation of surface water levels and discharge values. Manning’s roughness coefficient and river cross sections were defined for the calibration of observed river stage and discharge data. The predicted discharge was in good agreement with that of the observed discharge value. Study results illustrated that accuracy of predicted maximum water depth, and surface water level depends upon the precise representation of Manning’s roughness. The study is useful for the prediction of the flood dynamics in the river regime with the change in riverbed morphology.