Subsurface flow and large-scale lateral saturated soil hydraulic conductivity in a Mediterranean hillslope with contrasting land uses

Abstract

The lateral saturated hydraulic conductivity,Ks,l, is the soil property that mostly governs subsurface flow in hillslopes. Determinations ofKs,lat the hillslope scale are expected to yield valuable information for interpreting and modeling hydrological processes since soil heterogeneities are functionally averaged in this case. However, these data are rare since the experiments are quite difficult and costly. In this investigation, that was carried out in Sardinia (Italy), large-scale determinations ofKs,lwere done in two adjacent hillslopes covered by a Mediterranean maquis and grass, respectively, with the following objectives: i) to evaluate the effect of land use change onKs,l, and ii) to compare estimates ofKs,lobtained under natural and artificial rainfall conditions. HigherKs,lvalues were obtained under the maquis than in the grassed soil since the soil macropore network was better connected in the maquis soil. The lateral conductivity increased sharply close to the soil surface. The sharp increase ofKs,lstarted at a larger depth for the maquis soil than the grassed one. TheKs,lvalues estimated during artificial rainfall experiments agreed with those obtained during the natural rainfall periods. For the grassed site, it was possible to detect a stabilization ofKs,lin the upper soil layer, suggesting that flow transport capacity of the soil pore system did not increase indefinitely. This study highlighted the importance of the experimental determination ofKs,lat the hillslope scale for subsurface modeling, and also as a benchmark for developing appropriate sampling methodologies based on near-point estimation ofKs,l.

Economic Evaluation of Hydrological Ecosystem Services in Mediterranean River Basins Applied to a Case Study in Southern Italy

“…The chosen value was assumed to be 5.16 € m −3 for the detention basin [67] (Autorità di Bacino dei FiumiTrigno, Biferno e Minori, Saccione e Fortore). This evaluation is consistent with that proposed by [68]. Thus, the presence of a forested area is economically equivalent to a water retention system that can contain the same water quantity.…”

Lateral Saturated Hydraulic Conductivity of Soil Horizons Evaluated in Large-Volume Soil Monoliths

“…This result suggested that in the monolith MB the characteristics of lateral drainage for small-saturated soil thicknesses of the hillslope were probably not fairly represented. Also, the water-table dynamics reported for the B horizon of this site by Pirastru et al [32] and Pirastru et al [38] further supported the idea that in MB the characteristics of soil lateral drainage were misrepresented. During the saturation phase of the experiment, we observed that an isolated, large pore located at the soil-restrictive layer interface quickly drained when water was initially supplied to the inflow pit.…”

“…Therefore, the saturated soil hydraulic conductivities were much greater in the sub-horizontal direction compared to the vertical conductivity. Pirastru et al [32] and Pirastru et al [38] observed, in piezometers augered to the restrictive layer, the water table rapidly depleted when it rose in the A horizon. Even under the heaviest rainfall, the water table never reached the soil surface, with the exception of the wells located at the foot slope, close to the stream.…”

“…For this reason, we took the relationship between K s,l and water-table depths reported in Pirastru et al [38] for the same site as a benchmark. The authors estimated soil average K s,l by combining measurements of drainage rates from a 2.5 m-long drain and water-table levels from two well transects extending 10 m upslope of the drain.…”

“…Therefore, this relationship was considered representative for the soil over a large area of the hillslope. Although specific K s,l values for soil horizons are not shown in Pirastru et al [38], these can easily be gathered by applying Equation (3) with the K s,l values of the large-scale relationship coupled with the prescribed soil depths and the corresponding water-table elevations. Having done this, mean specific large-scale K s,l values of 8000 mm·h −1 , 780 mm·h −1 and 180 mm·h −1 were calculated for the A, upper B and lower B soil layers, respectively.…”