EVALUATION OF -CONVERTING STAGE TO DISCHARGE USING NORMAL RATING CURVE FOR FLOOD ROUTING STUDIES

Abstract

Adoption of appropriate stage-discharge rating curve for correct assessment of discharge using the stage measurements commands a great deal of importance for the reason that erroneous assessment may lead to failure of a river valley project or may result in sub-optimal utilization of surface water resources. Since long, there is a practice of developing a unique single stage-discharge curve from the periodic measurements of stages and corresponding discharges in rivers. However, for unsteady flow, rating curves are not single valued. A given stage is associated with a range of flow rates and vice versa. Therefore, the method of developing a single stage-discharge rating curve and inferring corresponding discharge for a specified flood stage using it, leads to incorrect discharge estimate. Variation in inflow hydrograph due to hysteretic nature of stage—discharge curve, during rising and receding stages of a flood at the gauging site, as compared to discharge estimated conventionally on the basis of single valued rating curve, may significantly alter the nature and magnitude of routed hydrograph at the downstream reach, where flood estimate is required for various operational and design purposes. This study attempts to quantify the effect of neglecting hysteresys in rating curve on some pertinent characteristics of the routed hydrographs, such as peak discharge, peak stage, corresponding time to peaks and volume conservation...