On diurnal riparian zone groundwater-level and streamflow fluctuations

Gribovszki et al. (Gribovszki, Z., Kalicz, P., Szilagyi, J., Kucsara, M., 2008. Riparian zone evapotranspiration estimation from diurnal groundwater-level fluctuations. J. Hydrol.) recently reported a peculiar phase-shift in diurnal streamflow and riparian zone groundwater-level fluctuations during streamflow recession for a small forested watershed. Employing high-frequency (10 min) groundwater-level and streamflow measurements in a wooded riparian zone of a gaining stream they demonstrated that groundwater-level changes lagged behind that of streamflow changes by about 1–1.5 h. To check the validity of their claim, a 2D finite element numerical model of the coupled system of vadose and saturated zones was employed with diurnal fluctuations in evapotranspiration. The model successfully reproduced the reported phase-shift and produced diurnal groundwater and streamflow fluctuations similar in their characteristics to what was reported. This finding demonstrates that by observing a similar phase-shift in diurnal fluctuations between high-frequency streamflow rate (or stream stage) and groundwater-level measurements during recession flow conditions, does not, in itself, indicate that the stream section is a losing one.