Effective Hydraulic Properties of Stony Soils: Simulation, Laboratory Experiment and Modeling

Stony soils are soils with a considerable volume of rock fragments (RF). They influence the soil hydraulic properties (SHP), including the water retention curve (WRC) and hydraulic conductivity curve (HCC). However, because of the challenges in the measurement and modeling of SHP in stony soils, RF are normally neglected in hydrological and land surface modeling.

In the present study, we measured SHP of stony soils with volumetric RF contents up to 50 % (v/v) in the laboratory using the simplified evaporation method. Afterward, we applied Hydrus 2D/3D software to create virtual stony soils with impermeable RF up to 37.3 % (v/v) in three spatial dimensions, 3D. The evaporation and multistep unit gradient experiments were simulated for the virtual stony soils, and inverse modeling in 1D was applied to identify their effective SHP. The identified effective SHP by measurement and inverse modeling were used to evaluate the available scaling models of hydraulic conductivity, such as the simple scaling model based on only the volume of RF (Ravina and Magier, 1984), and the most recent model, GEM, proposed by Naseri et al. (2020).

From the lab experiments, we successfully identified SHP of these stony soils for pressure heads from near saturation to -1000 cm. We also found that scaling the WRC of the background soil based on the volume of rock fragments gave reasonable effective SHP for low RF content, but was not appropriate for the highly stony soils. A higher reduction in conductivity was visible compared to the predicted values by the model of Ravina and Magier. Furthermore, comparison of the evaluated scaling models displayed a better performance of the GEM model especially when volume of RF in soil was low.

 

References:

Naseri, M., Peters, A., Durner, W. and Iden, S.C., 2020. Effective hydraulic conductivity of stony soils: General effective medium theory. Advances in Water Resources, 146, p.103765. DOI: 103765doi.org/10.1016/j.advwatres.2020.103765.

Ravina, I. and Magier, J., 1984. Hydraulic conductivity and water retention of clay soils containing coarse fragments. Soil Science Society of America Journal, 48(4), pp.736-740. DOI: 10.2136/sssaj1984.03615995004800040008x.