Hydraulic geometry analyses of the Kohora River, Assam, India

The Hydraulic geometry is crucial for understanding the hydrodynamic behavior in fluvial system. The present research analyzes the variation of hydraulic geometry parameters at-a-station and downstream sites along the Kohora River, Assam (India) aiming to quantify the exponential correlation between these parameters and the river’s flow discharge. For this research, six hydrological stations C1,C2,C3,C4,C5 and C6 are utilized to investigate the cross sectional hydraulic properties of Kohora River which are located at various sites along the river course. For each cross-section, a range of hydraulic geometry parameters including width, depth and velocity are recorded at different locations, and subsequent discharge is computed based on these parameters. To complement field-based observations, Landsat 8 satellite imagery (30 m spatial resolution) was processed using ArcGIS 10.7.1 to assess the river basin characteristics. The vegetation characteristics were examined by applying the Normalized Difference Vegetation Index (NDVI), while surface water extent and moisture variability were analyzed through the Normalized Difference Water Index (NDWI), providing supporting insights into catchment conditions influencing fluvial processes. Based on the present study, the mean values of exponents b, f, m which represent the scaling rates of change in width, depth and velocity were determined to be 0.334, 0.538 and 0.134 while the average values of coefficients a, c, k were noted to be 4.46, 0.56, 0.40 for at-a-station hydraulic geometry. For downstream hydraulic geometry, the exponents b, f, and m were 0.2, 0.4, and 0.4, while the coefficients a, c, and k were 5.19, 0.57, and 0.35. These values indicate a positive exponential relationship between the downstream hydraulic geometry parameters and flow discharge in Kohora River. The outcome of the present study is expected to be applicable to improving the watershed management of the river basin.