Large‐scale lateral saturated soil hydraulic conductivity as a metric for the connectivity of subsurface flow paths at hillslope scale

Abstract

Lateral saturated soil hydraulic conductivity, K s,l , is the soil property governing subsurface water transfer in hillslopes, and the key parameter in many numerical models simulating hydrological processes at the hillslope and catchment scales. Likewise, the hydrological connectivity of the lateral flow paths plays a significant role in determining the rate of the subsurface flow at various spatial scales. This study investigates the relationship between K s,l and hydrological connectivity at the hillslope spatial scale. K s,l was determined by the subsurface flow rates intercepted by drains and water table depths observed in a well network. The hydrological connectivity was evaluated by the synchronicity among water table peaks, and between these and the peaks of the drained flow. Rainfall and soil moisture were used to investigate the influence of the transient hydrological soil condition on connectivity and K s,l . As the synchronicity of the water table response between wells increased, the lag times between the peaks of water levels and those of the drained subsurface flow decreased. Moreover, the most synchronic water table rises determined the highest drainage rates. The relationships between K s,l and water table depths were highly non-linear, with a sharp increase in the values for water table levels close to the soil surface. Estimated K s,l values for the full saturated soil were in the order of thousands of mm h À1 , suggesting the activation of macropores in the root zone. The K s,l values determined at the peak of the drainage events were correlated with the indicators of synchronicity. The sum of cumulative rainfall and antecedent soil moisture was correlated with the connectivity indicators and K s,l . We suggest that, for simulating realistic processes at the hillslope scale, the hydrological connectivity could be implicitly considered in hydrological modelling through an evaluation of K s,l at the same spatial scale.

Impacts of Topography‐Driven Water Redistribution on Terrestrial Water Storage Change in California Through Ecosystem Responses

“…Numerous laboratory-based and field-based methods have been developed to measure small-scale (e.g., small soil cores) k s,l (Dorsey et al, 1990;Mohanty et al, 1994;Youngs, 1987). However, small-scale k s,l measurements consistently underestimate large-scale (e.g., hillslope-scale) k s,l due to the lack of information about spatial heterogeneity, especially in the fields where macropores are present (Brooks et al, 2004) Pirastru et al, 2022). Therefore, modelers usually calibrate k s,l based on streamflow/baseflow or simply by relating ζ with the clay content (Beven et al, 1995;Chen & Kumar, 2001;Fan et al, 2007;Grayson et al, 1992;Kumar, 2004;Wigmosta et al, 1994;Zeng et al, 2016).…”

“…However, small‐scale k s , l measurements consistently underestimate large‐scale (e.g., hillslope‐scale) k s , l due to the lack of information about spatial heterogeneity, especially in the fields where macropores are present (Brooks et al., 2004). Due to the high experimental cost, only a few studies have estimated hillslope‐scale k s , l through trench and drains experiments (Brooks et al., 2004; Chappell & Lancaster, 2007; Dunne & Black, 1970; Pirastru et al., 2022). Therefore, modelers usually calibrate k s , l based on streamflow/baseflow or simply by relating ζ with the clay content (Beven et al., 1995; Chen & Kumar, 2001; Fan et al., 2007; Grayson et al., 1992; Kumar, 2004; Wigmosta et al., 1994; Zeng et al., 2016).…”

Network dynamics for modelling artificial groundwater recharge by a cluster of infiltration basins

“…This modelling interest can be tailored also according to particular hydrological regimes (e.g., Chui & Trinh, 2016), whereas the impact of infiltration facilities over the groundwater recharge and its seasonality has been recently studied in (Samanta et al, 2020). On the other hand, the interest in characterizing hydraulic conductivity at a large scale is still a challenging research problem (e.g., Pirastru et al, 2022).…”

“…This modelling interest can be tailored also according to particular hydrological regimes (e.g., Chui & Trinh, 2016), whereas the impact of infiltration facilities over the groundwater recharge and its seasonality has been recently studied in (Samanta et al, 2020). On the other hand, the interest in characterizing hydraulic conductivity at a large scale is still a challenging research problem (e.g., Pirastru et al, 2022). Furthermore, if large volumes of water infiltrate, a correct modelling of such ponds cluster could also help in assessing how they contribute to groundwater recharge, even in karst and heterogeneous aquifers (e.g., Allocca et al, 2014).…”

“…In comparison with (Freni et al, 2009), in which the Green-Ampt model is used, our approach makes use of the even simpler Darcy's law: where in (Freni et al, 2009) the effective infiltration area is assumed to be "the horizontal area below the structure bottom where the infiltration paths start to be linear and vertical parallel", here, from observation evidence, a significant role is played by lateral infiltration, both amongst adjacent basins and through lateral external walls of basins system. On the other hand, unlike urban infiltration trenches, designed for handling stormwater runoff, such infiltration basins generally work in saturation conditions, therefore the Darcy approach is even more so justified; furthermore, for such management practices, addressing the solution of Richards equation, with the well-known numerical difficulties (see, for instance, Abreu et al, 2019;Berardi & Difonzo, 2022;Berardi et al, 2018;Pop et al, 2004;Zhu et al, 2022) is cumbersome: we point out that multidimensional unsaturated flow models are "rarely applied in the design of stormwater infiltration systems because of their data and expertise requirements and complexity" (Browne et al, 2013).…”