Analytical approximations of discharge recessions for steeply sloping aquifers in alpine catchments

The validity and applicability of various methods to infer hydraulic properties of sloping aquifers in alpine settings using the power law relationship between the discharge recession and its first time derivative is explored. For this purpose, a synthetic spring catchment implemented in the numerical groundwater flow model MODFLOW as well as the example of a relict rock glacier in an alpine setting is examined. The various approaches are found to differ particularly in the late time domain, whereas most of them agree fairly well in the early time domain and at the transition point between the two time domains. As the early recession may be affected by uncertainties from inappropriate initial conditions, it is proposed to use the transition point for estimating aquifer thickness and transmissivity. Using only prolonged winter recessions in the analysis of the field data from the relict rock glacier yields estimates of aquifer thickness and hydraulic conductivity consistent with results from a geophysical survey and tracer tests, respectively. In the other seasons, the recession is frequently interrupted by minor recharge events, and using the lower envelope of the entire data is found to yield estimates that are too high in the given case. It is thus recommended to focus on the winter recession in the analysis of hydrograph data from alpine settings.