Comparison of Spatial Scaling of Peak Discharge in Caspian Sea Basins and Karkheh Basin

Abstact:The relationship between peak flood and watershed area has always ben used for predition at ungaged basins. In a region with homogenous hydrologic resonse this relationship changes with a similar ratio which is called simple saling. If this ratio changes it would result in multiscaling relationship between peak floos and watrshed area and therefore, basin area cannot be used for flood discharge estimation at ungagfed basin alone. Therfore it is necessary ro evalute this before developing regional flood model.This study investigates the spatial scale method in two Caspian Sea basin and Karkheh river basin and then compares the results of two basin. To this end, peak discharge for the 46 hydrometric stations in the Caspian Basin and 24 stations in the Karkheh basin have been selected. These stations have similar hydrological behavior among the stations in their basin. The statistical method of the spatial scale at these stations was performed using the probability weight moments of annual peak discharge and area covered by each station. The results showed that in the Caspian Sea basin the parameter of the spatial scale is simple and in the Karkhe basin the multiscale mode of the spatial scale exists. Therefore, it can be said that for estimating the discharge in the ungaged regions for the Karkheh basin, it is not possible to use the flood index and the discharge-area power relationship. While this is feasible in the Caspian Sea basin.