Hydrograph separation of runoff components based on measuring hydraulic state variables, tracer experiments and weighting methods

Presented at the XXII General Assembly of the International Union on Geodesy and Geophysics
Birmingham, UK, 1999

abstract

Hydrograph separation with natural tracers or isotopes has become a popular method to gain comprehensive insights into runoff processes. The mass balance approach, which uses the measured chemical signature of the rainfall as the signature of the event water, is generally used for this purpose. However, temporal variations in the composition of rainfall must be taken into account by an appropriate weighting technique that describes the time response of event water in a drainage basin. A conservative tracer was added to an artificially simulated intense rainfall event on a small forested hillslope plot. A simple mass balance approach coupled with an appropriate weighting technique was used to separate the event and pre-event water fractions of the surface and subsurface flow. Runoff processes and their relation to mixing between event and pre-event water are identified for both flow paths by means of a detailed survey of both soil water changes and soil properties, as well as through a dye tracer experiment. The experiment demonstrates the importance of event water contributions to subsurface runoff by preferential flow.

© Markus Weiler 4/2001