Capillary Barriers: Design Variables and Water Balance

Abstract

Water balance simulations were conducted with the unsaturated flow model UNSAT-H to assess how layer thicknesses, unsaturated hydraulic properties, and climate affect the performance of capillary barriers. Simulations were conducted for four locations in semiarid and arid climates. Hydraulic properties of four finergrained and two coarser-grained soils were selected to study how saturated and unsaturated hydraulic properties affect the water balance. Results of the simulations indicate that thickness and hydraulic properties of the surface layer significantly affect the water balance of capillary barriers. As expected, increasing the thickness or reducing the saturated hydraulic conductivity of the finer-grained surface layer reduces percolation. Unsaturated hydraulic properties of the coarser layer also affect the water balance, including the storage capacity of the surface layer as well as the onset and amount of percolation from the cover. Thickness of the coarser layer has a much smaller impact on the water balance. Climate also affects the water balance. Greater soil water storage capacity is required at sites where the season with more frequent and less intense precipitation does not coincide with the season having highest evapotranspiration.

Observations of capillary barriers and preferential flow in layered snow during cold laboratory experiments

“…This impedance is usually referred to as a capillary barrier (Khire et al, 2000;Waldner et al, 2004) and is due to the infiltrating water being generally marked by a very high suction when it initially moves in the finer layer. This prevents water from entering the lower layer, thus causing local accumulation of water at the interface (henceforth, simply ponding), a deceleration in the undisturbed advancement of the wetting front, horizontal diversion of water, and a delay in the expected travel time of water.…”

“…This prevents water from entering the lower layer, thus causing local accumulation of water at the interface (henceforth, simply ponding), a deceleration in the undisturbed advancement of the wetting front, horizontal diversion of water, and a delay in the expected travel time of water. Hill and Parlange (1972), Baker and Hillel (1990), Hillel and Baker (1988), Stormont and Morris (1998), Stormont and Anderson (1999), and Khire et al (2000) discuss this process in soils, whereas Wakahama (1963), Jordan (1995), Waldner et al (2004), Peitzsch et al (2008), and Mitterer et al (2011) report some examples for layered snowpack. According to the results by Stormont and Anderson (1999) in soils, water will enter the underlying coarser layer when ψ at the interface decreases to ψ WE ; at this suction, the coarser soil layer firstly becomes conductive (Stormont and Morris, 1998;Khire et al, 2000).…”

Postconstruction Changes in the Hydraulic Properties of Water Balance Cover Soils

“…Cover soils with higher K s , more gradually varying K  , and a SWCC with higher air entry suction generally transmit less surface runoff and more percolation (drainage from the base of the cover) (Fayer and Gee 1997, Khire et al 2000, Roesler et al 2002, Apiwantragoon et al 2003, Zornberg et al 2003, Benson et al 2005.…”

“…When long-term analyses of cover hydrology are made, temporal changes in soil properties are assumed or inferred because few data exist regarding how hydraulic properties change over time (Khire et al 2000, Zornberg et al 2003, Waugh et al 1994, 1999. This paper compares hydraulic properties of cover soils measured at the time of construction and 1-4 yr after construction, provides methods to estimate changes in the hydraulic properties over time, and provides recommendations regarding cover construction methods that will minimize the propensity for change in hydraulic properties.…”

Design Solutions for Lithuanian Gravel Road Pavements

“…The deformation modulus of reconstructed roads on the formation level is heterogeneous and the following characteristics of soil influence it: type, relative moisture content, etc [7,8]. When designing pavements of reconstructed gravel roads, the characteristics of the existing subgrade soils will also be taken into consideration.…”