Using an inverse modelling approach to evaluate the water retention in a simple water harvesting technique

摘要

In arid and semi-arid zones, runoff harvesting techniques are oftenapplied to increase the water retention and infiltration on steepslopes. Additionally, they act as an erosion control measure toreduce land degradation hazards. Nevertheless, few efforts wereobserved to quantify the water harvesting processes of thesetechniques and to evaluate their efficiency. In this study, acombination of detailed field measurements and modelling with theHYDRUS-2D software package was used to visualize the effect of aninfiltration trench on the soil water content of a bare slope innorthern Chile. Rainfall simulations were combined with high spatialand temporal resolution water content monitoring in order toconstruct a useful dataset for inverse modelling purposes. Initialestimates of model parameters were provided by detailed infiltrationand soil water retention measurements. Four different measurementtechniques were used to determine the saturated hydraulicconductivity (K_sat) independently. The tensioninfiltrometer measurements proved a good estimator of the K_sat value and a proxy for those measured under simulated rainfall,whereas the pressure and constant head well infiltrometermeasurements showed larger variability. Six different parameteroptimization functions were tested as a combination of soil-watercontent, water retention and cumulative infiltration data.Infiltration data alone proved insufficient to obtain high modelaccuracy, due to large scatter on the data set, and water contentdata were needed to obtain optimized effective parameter sets withsmall confidence intervals. Correlation between the observed soilwater content and the simulated values was as high as R2=0.93for ten selected observation points used in the model calibrationphase, with overall correlation for the 22 observation points equalto 0.85. The model results indicate that the infiltration trench hasa significant effect on soil-water storage, especially at the baseof the trench.