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

Abstract

Abstract. In arid and semi-arid zones, runoff harvesting techniques are often applied to increase the water retention and infiltration on steep slopes. Additionally, they act as an erosion control measure to reduce land degradation hazards. Nevertheless, few efforts were observed to quantify the water harvesting processes of these techniques and to evaluate their efficiency. In this study, a combination of detailed field measurements and modelling with the HYDRUS-2D software package was used to visualize the effect of an infiltration trench on the soil water content of a bare slope in northern Chile. Rainfall simulations were combined with high spatial and temporal resolution water content monitoring in order to construct a useful dataset for inverse modelling purposes. Initial estimates of model parameters were provided by detailed infiltration and soil water retention measurements. Four different measurement techniques were used to determine the saturated hydraulic conductivity (K sat ) independently. The tension infiltrometer 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 infiltrometer measurements showed larger variability. Six different parameter optimization functions were tested as a combination of soil-water content, water retention and cumulative infiltration data. Infiltration data alone proved insufficient to obtain high model accuracy, due to large scatter on the data set, and water content data were needed to obtain optimized effective parameter sets with small confidence intervals. Correlation between the observed soil water content and the simulated values was as high as R 2 =0.93 for ten selected observation points used in the model calibration phase, with overall correlation for Correspondence to: K. Verbist (koen.verbist@ugent.be) the 22 observation points equal to 0.85. The model results indicate that the infiltration trench has a significant effect on soil-water storage, especially at the base of the trench.

Parameterizing a Coupled Surface–Subsurface Three‐Dimensional Soil Hydrological Model to Evaluate the Efficiency of a Runoff Water Harvesting Technique

“…A second objective of this case study was to evaluate a runoff water harvesting technique (RWH) in a novel framework. In this respect, the final model also effectively simulated trench overfilling, which was not considered in previous one‐dimensional (Boers et al, 1986; Martínez de Azagra, 1996; Young et al, 2002) or two dimensional water harvesting modeling efforts (Verbist et al, 2009). Due to the coupled nature of the model, the three‐dimensional HydroGeoSphere model will be more appropriate to simulate the overland flow routing on hillslopes with complex microtopography and where interaction of different water harvesting techniques due to overfilling is important.…”

“…The use of the inverse modeling technique for soil hydrological modeling has seen a steady increase, with applications extending beyond the original laboratory approach (Parker et al, 1985) toward progressively more complex field applications (Ritter et al, 2003; Verbist et al, 2009; Wöhling and Vrugt, 2011; Wollschläger et al, 2009). Extension of this modeling methodology to evaluate and improve existing ancient conservation structures, such as many RWH techniques, has a large potential (van Genuchten and Šimůnek, 2004), but few test cases have been reported.…”

“…Extension of this modeling methodology to evaluate and improve existing ancient conservation structures, such as many RWH techniques, has a large potential (van Genuchten and Šimůnek, 2004), but few test cases have been reported. In Verbist et al (2009) the HYDRUS‐two‐dimensional subsurface model (Šimŭnek et al, 1999b) was calibrated for a water harvesting trench based on a detailed set of field measurements under simulated rainfall, resulting in an adequate simulation of the observed moisture contents. Nevertheless, this approach proved inadequate to evaluate the water harvesting efficiency or to determine the optimal dimensions of the RWH technique, since surface runoff could not be specifically accounted for.…”

Development and testing of a large, transportable rainfall simulator for plot-scale runoff and parameter estimation

“…Alberts et al (1995) demonstrated a sufficient fit of an infiltration model to observed data can be found by running the model with a range of values for the saturated hydraulic conductivity and selecting the value that minimizes model error with respect to the observed infiltration. This method can be applied here to obtain K s,bulk and K s,surf from the experiment data in a similar manner as Verbist et al (2009). Here, we define K s,surf and K s,bulk to be the saturated hydraulic conductivities of the surface layer and remainder of the soil profile, respectively.…”

Towards systematic planning of small-scale hydrological intervention-based research

“…A study on trenches in Chile by Verbist et al (2009) suggested that only few cases did quantify the (positive) effect of runoff water harvesting techniques on water retention. One older study, Doty (1972), found that almost no change in soil water between areas with and without trenches.…”