Technical note: How physically based is hydrograph separation by recursive digital filtering?

Abstract

Abstract. Recursive digital filtering of hydrographs is a widely used method to identify streamflow components, which react to precipitation with varying degrees of attenuation and delay. In this context, a distinction is often made between physically based and non-physically based algorithms. A well-known example of a physically based algorithm is that of Furey and Gupta (2001). In this paper, it is contrasted with the widely used algorithm of Eckhardt (2005). This algorithm is often considered merely a non-physically based low-pass filter. However, the comparison shows that both algorithms largely agree. The algorithm of Eckhardt (2005) differs from the algorithm of Furey and Gupta (2001) only in the time delay assumed between precipitation and the exfiltration of baseflow into surface waters and in the fact that two parameters are combined into one, BFImax. This parameter can thus be interpreted physically, and an approach for its calculation emerges.