Numerical simulation of unsaturated flow along preferential pathways: implications for the use of mass balance calculations for isotope storm hydrograph separation

A review of model applications for structured soils: a) Water flow and tracer transport

“…This explained the (frequently) observed dominance of pre-event water in runoff events . Van Der Hoven et al (2002) also investigated how to separate storm hydrographs into pre-event water and stormevent water, but based on the δ 18 O natural isotope content. While this is a problem relevant to catchment scale, the experimental analysis of δ 18 O values in shallow groundwater focussed on one multi-port well in fractured saprolite.…”

“…Results suggested that the δ 18 O content was not constant over the course of a storm event, and that most of the matrix water was isolated from flow in fractures. It was concluded that quantitative hydrograph separation using isotope techniques is not possible in most situations (Van Der Hoven et al, 2002). Christiansen et al (2004) coupled the 1D vadose zone -3D groundwater hydrology model MIKE SHE operating at the catchment scale (Refsgaard and Storm, 1995), the 1D agroecosystem model DAISY (Hansen et al, 1991;Abrahamsen and Hansen, 2000), and a 1D DPM based on MACRO (Jarvis, 1994).…”

Hillslope hydrograph analysis using synthetic and natural oxygen-18 signatures

“…These restrictions often limit the applicability of runoff separation using isotope data (Van der Hoven et al, 2002). As pointed out by Van der Hoven et al (2002), the measurement of a single 18 O value to characterize the pre-event isotopic composition of soil water in the entire soil profile is hardly adequate. For instance, Kendall and McDonnell (1993) inspected the effect of variable isotope concentration depth profiles on hydrograph separation.…”

“…Jones et al (2006) argued that the role of tracer dispersion is neglected in the hydrograph separation procedures. Van der Hoven et al (2002) questioned validity of most hydrograph separation studies reported in the literature, which did not consider spatial and temporal variability in individual compartments of subsurface reservoirs. Similarly, Uhlenbrook and Hoeg (2003) demonstrated that the hydrograph separation might deliver only qualitative information on the different runoff contributions while relatively large uncertainties of various sources prevailed when performing the separation.…”

Uncertainty Analysis of the Tracer-Based Hydrograph Separation Method

“…Tayoko et al reported that there was a relative difference of about 5%-10% in calculated results, which determined by the isotopic compositions of the rain [7]. In practice, the isotopic compositions of precipitation effected by many relevant factors including the source of air masses, the running path, the temperature of condensation, the terrain conditions and so on [8], [9], may have great space-time variability.Moreover, the isotopic compositions of groundwater in the process of rainfall-runoff also have great changes [10], owing to the influence of event precipitation and movement path in natural basins. Therefore, it seems important to consider the spatial and temporal variability of component isotopic composition, and analyze the uncertainty of hydrograph separation.…”