15 Jun 2022
15 Jun 2022
Status: a revised version of this preprint is currently under review for the journal HESS.

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

Klaus Eckhardt Klaus Eckhardt
  • University of Applied Sciences Weihenstephan-Triesdorf, Weidenbach, 91746, Germany

Abstract. Recursive digital filtering of hydrographs is a widely used method to identify the groundwater-borne portion of streamflow. In this context, a distinction is often made between physically based and non-physically based algorithms. The algorithm of Furey and Gupta (2001), for example, is counted among the former. In this paper, it is contrasted with the algorithm of Eckhardt (2005). This algorithm represents a whole class of recursive digital filters based on the assumption that the aquifer is a linear reservoir. It is shown that the algorithm of Eckhardt (2005) is not merely a low-pass filter, but that it is largely identical to the aforementioned physically based algorithm of Furey and Gupta (2001). 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 groundwater 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.

Klaus Eckhardt

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on hess-2022-186', Keith Beven, 23 Jun 2022
    • AC1: 'Reply on CC1', Klaus Eckhardt, 28 Jun 2022
      • CC2: 'Reply on AC1', Keith Beven, 28 Jun 2022
        • AC2: 'Reply on CC2', Klaus Eckhardt, 07 Jul 2022
  • RC1: 'Comment on hess-2022-186', Anonymous Referee #1, 04 Aug 2022
    • AC3: 'Reply on RC1', Klaus Eckhardt, 06 Aug 2022
  • RC2: 'Comment on hess-2022-186', Anonymous Referee #2, 11 Aug 2022

Klaus Eckhardt

Klaus Eckhardt


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Short summary
An important hydrological question is what proportion of the runoff in a surface water body comes from groundwater. This proportion is also called baseflow. Among the multitude of methods that have been developed to identify baseflow, a specific, frequently used one is singled out here. It is shown to be derived from plausible physical principles. This increases confidence in its results.