Discharge Estimation in a Backwater Affected River Junction Using HPG

Abstract

This study presents a method for estimating discharge at a stage-gauging station located in a backwater affected river junction. A hydraulic performance graph (HPG) summarizing the backwater profiles on all possible flow conditions was applied to the river system at the juncture of the main stream and the tributary. The HEC-RAS model for dendritic river was created, and the unsteady simulation was implemented for calibration and verification. The relationship between two water levels from existing stage stations at the main stream and the tributary and the discharge at the backwater affected section was estimated, and kriging interpolation was carried out. During a flood, the discharge was calculated using kriging-interpolated HPG and the water level measurements at two stage stations. It was then validated by comparing the automatic discharge measurements from ADVM. The result provides an economical and practical method for estimating discharge in a junction with a high hysteresis of looped stage- discharge relationships. River discharge observation data has been used in several fields including water balance, flood prediction, dam and reservoir operation, the design of hydraulic structures, water supply, and aquatic ecosystem conservation. It is essential data for the examination and calibration of rainfall-runoff models and flood routing models. Generally, discharge is observed directly through a field survey, but in the consideration of time and cost, it is difficult to observe discharge continuously for a long period of time. Therefore, in order to observe discharge, we use an indirect method to prepare a stage-discharge relation curve from empirical relationships between the observed discharge and water level of river for a limited period and convert the measured water level into discharge by applying the measured water level to this curve.