Discharge estimation and rating curve derivation, using satellite geometry data and isovel contours at Karun River, Iran

Determining discharge and stage–discharge curves in fluvial environments without hydrometric gauges is a critical challenge in hydrologic studies and river hydraulics. This issue will be more evident in managing flood hazards in the rivers of arid areas without flow measurement gauges, where the reaction time is the critical factor. Researchers and designers have always tried to access simpler, cheaper methods to estimate discharge and rating curves. This research aims to facilitate the determination of the discharge and stage–discharge relationship by applying remote sensing techniques and the concept of isovel contours. For this purpose, the geometry of the river cross section is determined using remotely sensed data from the images of the Sentinel-1 and two satellites, and then discharge passed through the cross section is estimated by the single point velocity measurement method. The observed data were collected from the Mollasani station in Karun River, Iran, to confirm this method. The obtained discharges and stage–discharge relationship curves are used to evaluate the accuracy of the proposed methodology. Statistical analyses showed that the mean value of the normalized percentage error and mean absolute percentage error (MAPE) calculated based on the difference between the estimated and observed discharges are limited to 6.3 and 8.36%, respectively. Also, the stage–discharge curves in these studies were estimated with a maximum MAPE of 9.5%, which is considered a good initial approximation considering the minimum required data.