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Open access

Michal Dohnal, Tomáš Vogel, Martin Šanda and Vladimíra Jelínková

Uncertainty Analysis of a Dual-Continuum Model Used to Simulate Subsurface Hillslope Runoff Involving Oxygen-18 as Natural Tracer

A one-dimensional dual-continuum model (also known as dual-permeability model) was used to simulate the lateral component of subsurface runoff and variations in the natural 18O content in hillslope discharge. Model predictions were analyzed using the GLUE generalized likelihood uncertainty estimation procedure. Model sensitivity was evaluated by varying two separate triplets of parameters. The first triplet consisted of key parameters determining the preferential flow regime, i.e., the volumetric proportion of the preferential flow domain, a first-order transfer coefficient characterizing soil water exchange between the two flow domains of the dual-continuum system, and the saturated hydraulic conductivity of the preferential flow domain. The second triplet involved parameters controlling exclusively the soil hydraulic properties of the preferential flow domain, i.e., its retention curve and hydraulic conductivity function. Results of the analysis suggest high sensitivity to all parameters of the first triplet, and large differences in sensitivity to the parameters of the second triplet. The sensitivity analysis also confirmed a significant improvement in the identifiability of preferential flow parameters when 18O content was added to the objective function.

Open access

Jana Votrubova, Michal Dohnal, Tomas Vogel, Miroslav Tesar, Vladimira Jelinkova and Milena Cislerova

Abstract

Temporal variability of the soil hydraulic properties is still an open issue. The present study deals with results of ponded infiltration experiments performed annually in a grid of permanent measurement points (18 spatial and 14 temporal replicates). Single ring infiltrometers were installed in 2003 at a meadow site in the Bohemian Forest highlands, the Czech Republic. The soil at the plot is coarse sandy loam classified as oligotrophic Eutric Cambisol. Soil water flow below infiltration rings has distinctly preferential character.

The results are marked with substantial interannual changes of observed infiltration rates. Considering just the results from the initial four years of the study, the temporal variability did not exceed the spatial variability detected in individual years. In later years, a shift to extremely high infiltration rates was observed. We hypothesize that it is related to structural changes of the soil profile possibly related to combined effect of soil biota activity, climatic conditions and experimental procedure. Interestingly, the temporal changes can partly be described as fluctuations between seemingly stable infiltration modes. This phenomenon was detected in the majority of rings and was found independent of the initial soil moisture conditions.