[1] The distributed predictions of the original version of TOPMODEL are here compared with distributed observations of water table levels in the Uhlirska catchment in the Jizera Mountains, Czech Republic. The calibration of the model has been carried out within the GLUE framework, which allows the estimation of uncertainties in predicting the distributed patterns of the water table at different times. Many of the water table levels are predicted within the limits of uncertainty, but it is shown that the predictions could be improved by the calculation of a local effective transmissivity value (or local upslope contributing areas) at each observation site. These effective transmissivities show a similar relationship to the topographic index as found in a previous study of a small catchment in Norway. Some of the anomalies can be explained by deficiencies in the topographic analysis but this may also be an indication of possible structural deficiencies in the model. Interpretation is, however, difficult, and it remains to be seen whether these anomalies they might be avoided in more dynamic distributed models.
This paper focuses on numerical modelling of soil water movement in response to the root water uptake that is driven by transpiration. The flow of water in a lysimeter, installed at a grass covered hillslope site in a small headwater catchment, is analysed by means of numerical simulation. The lysimeter system provides a well defined control volume with boundary fluxes measured and soil water pressure continuously monitored. The evapotranspiration intensity is estimated by the Penman-Monteith method and compared with the measured lysimeter soil water loss and the simulated root water uptake. Variably saturated flow of water in the lysimeter is simulated using one-dimensional dual-permeability model based on the numerical solution of the Richards’ equation. The availability of water for the root water uptake is determined by the evaluation of the plant water stress function, integrated in the soil water flow model. Different lower boundary conditions are tested to compare the soil water dynamics inside and outside the lysimeter. Special attention is paid to the possible influence of the preferential flow effects on the lysimeter soil water balance. The adopted modelling approach provides a useful and flexible framework for numerical analysis of soil water dynamics in response to the plant transpiration.
In order to evaluate the proportion of old and new water in drainage runoff, we recorded air temperature, drainage discharge, drainage runoff temperature, soil temperature, precipitation totals, and temperature. The results of separation by temperature were compared with the results of chemical separation using the stable isotopes δ 18O and δ 2H measured in causal precipitation and monitored in drainage runoff. Separation was determined based on precipitation temperature in 18 rainfall–runoff events and on soil temperature in 20 rainfall–runoff events, with no significant difference between results of separation of drainage runoff based on temperature and that based on isotopes. Separation of runoff based on temperature is feasible only for simple isolated rainfall–runoff events as opposed to those involving multiple rainfalls. Time to peak discharge was identified as a viable factor to determine whether to employ separation based on soil temperature or on precipitation temperature. Time to peak discharge showed a strong correlation with the intensity of precipitation. The results suggest that, conditional on analysis of a larger dataset, isotope separation of drainage runoff and, possibly, runoff in watercourses may potentially be replaced with more economical and technically simple measurement of soil and precipitation/air temperature.
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