Abstract
Evaluating the lateral saturated hydraulic conductivity, Ks,l, of soil horizons is crucial for understanding and modelling the subsurface flow dynamics in many shallow hill soils. A Ks,l measurement method should be able to catch the effects of soil heterogeneities governing hydrological processes at the scale of interest, in order to yield Ks,l representative values over large spatial scales. This study aims to develop a field technique to determine spatially representative Ks,l values of soil horizons of an experimental hillslope. Drainage experiments were performed on soil monoliths of about 0.12 m3 volume, encased in situ with polyurethane foam. Median Ks,l of 2450 mm·h−1 and 552 mm·h−1 were estimated in the A and B horizon, respectively. In the upper part of the B horizon, the median Ks,l was 490 mm·h−1, whereas it mostly halved near the underlying restricting layer. The decline of Ks,l values with depth was consistent with the water-table dynamics observed at the same site in previous studies. Moreover, the Ks,l from the monoliths were in line with large spatial-scale Ks,l values reported from the hillslope in a prior investigation based on drain data analysis. This indicated that the large-scale hydrological effects of the macropore network were well represented in the investigated soil blocks. Our findings suggest that performing drainage experiments on large-volume monoliths is a promising method for characterizing lateral conductivities over large spatial scales. This information could improve our understanding of hydrological processes and can be used to parameterize runoff-generation models at hillslope and catchment scale.
Highlights
IntroductionIn many hillslopes with shallow steep soils, the spatial and temporal dynamics of the perched water table are dominated by the lateral (namely slope-parallel) saturated subsurface flow
In many hillslopes with shallow steep soils, the spatial and temporal dynamics of the perched water table are dominated by the lateral saturated subsurface flow
By imposing decreasing water levels in the monolith pits during the drainage experiments, the Ks,l values of three decreasing saturated soil thicknesses on the restrictive layer were computed for each monolith by using Equation (1)
Summary
In many hillslopes with shallow steep soils, the spatial and temporal dynamics of the perched water table are dominated by the lateral (namely slope-parallel) saturated subsurface flow. These water tables often originate from infiltrated precipitation that is hindered from further downwards percolation by restrictive layers beneath soils, e.g., fragipan in [1], argillic Bt horizon in [2], and weathered granite in [3]. The lateral saturated hydraulic conductivity, Ks,l , is the soil property that influences transmission rate of the lateral subsurface water flow [9,10].
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