Does discharge time source correspond to its geographic source in hydrograph separations? Toward identification of dominant runoff processes in a 300 square kilometer watershed

Abstract. This study compared a time source hydrograph separation method to a geographic source separation method, to assess if the two methods produced similar results. The time source separation of a hydrograph was performed using a numerical filter method and the geographic source separation was performed using an end-member mixing analysis employing hourly discharge, electric conductivity, and turbidity data. These data were collected in 2006 at the Kuroiwa monitoring station on the Abukuma River, Japan. The results of the methods corresponded well in terms of both surface flow components and inter-flow components. In terms of the baseflow component, the result of the time source separation method corresponded with the moving average of the baseflow calculated by the geographic source separation method. These results suggest that the time source separation method is not only able to estimate numerical values for the discharge components, but that the estimates are also reasonable from a geographical viewpoint in the 3000 km² watershed discussed in this study. The consistent results obtained using the time source and geographic source separation methods demonstrate that it is possible to characterize dominant runoff processes using hourly discharge data, thereby enhancing our capability to interpret the dominant runoff processes of a watershed using observed discharge data alone.