Development and Analysis of Discharge Rating Curve for Kojour Educational Forest Watershed in Different Time Scales

The permanent measurement of discharge even in general conditions is difficult and very expensive and the related problem is increased when floods take place. Towards solving the problem, it is tried to develop discharge-stage relationship through reading the stage and measuring the associated discharge in particular conditions. In this study, the stage-discharge relationship was developed and then analyzed for different time scales of rising and falling limbs of hydrographs, daily, monthly and seasonal by using bivariate regression and classic discharge rating models. The study was conducted in Kojour Forest Educational Watershed with an area of 13253 ha in Mazandaran Province, Iran. The results showed that the developed relationships, for each time scale, are specific, so that they cannot be applied for the other scales with reliable accuracy. The linear and power regression models with the minimum correlation coefficient of 58%, the maximum respective calibration and verification relative errors of 70 and 75%, lower RMSE and the minimum efficiency coefficient of 35% were also found superior to and more accurate than classics models for all study time scales.