Gravity‐Driven and Viscosity‐Dominated Infiltration into a Full‐Scale Sand Model

Abstract

Data from an infiltration and drainage experiment into and from a sand tank model of 5 by 3 m and 2 m deep were reevaluated. The uniform sand overlaid a 0.2‐m‐thick gravel layer from which five perforated pipes collected drainage flow. The data include time series of capillary potentials, ψ, volumetric water contents, θ, both from nine levels, and drainage flow, q, that resulted from sprinkler infiltration with a constant rate of 15.6 mm h−1 that lasted >16 h. The wetting and the pressure fronts (i.e., the increases of water content and of capillary potential) moved with the same constant velocity of 3.25 × 10−5 m s−1 The capillary potentials about 0.2 to 0.4 m behind the wetting front remained constant at about −2.5 kPa. The maximum degree of saturation during infiltration was <0.6 and the mobile water content involved in flow was about 0.15 m3 m−3 The constant velocity indicates a continuous and dynamic balance of forces acting on the mobile water. Thus, viscosity is considered to have balanced gravity as the driving force, and a momentum dissipation approach to infiltration evolved. Capillary and Bond numbers indicate that flow was subjected to considerable capillary potential, yet its gradient was only active throughout a depth range of 0.2 to 0.4 m behind the wetting front. The constant velocity prevailed despite local variations in the mobile water content. Constant velocity of wetting is proposed as the global key parameter during infiltration on which local features, like volume flux density and variation of water content, may depend.

Viscous‐Flow Approach to In Situ Infiltration and In Vitro Saturated Hydraulic Conductivity Determination

“…There are indications that viscous flow is rather tolerant on permeable‐media lengths. The applicability of viscous flow to infiltration and drainage has been demonstrated in numerous cases, ranging from the submillimeter to the meter scale (see, for instance, Hincapié and Germann, 2009c; Germann and al Hagrey, 2008). Moreover, Dubois (1991) reported approximate wetting front velocities of v = 2 × 10 −4 m s −1 in crystalline rocks of the Mont Blanc massif in the three‐corner region of France, Italy, and Switzerland.…”

“…Further, no trend with depth of the gradual increases in θ( Z m , t ) from θ in to θ max was discernible. Thus, Germann and al Hagrey (2008) concluded that the gradual increase was due to local processes most likely occurring within the control volume of the TDR probes. Germann (2014) provided additional clues on the gradual increase of θ( Z m , t ).…”

Greater abundance of Fagus sylvatica in coniferous flood protection forests due to climate change: impact of modified root densities on infiltration

“…According to Germann and al Hagrey (2008), the wcw's average wetting front velocity from the soil surface to depth …”

Viscosity—The weak link between Darcy's law and Richards' capillary flow

“…Thus, constant v ac during infiltration indicates constant rigidity of the medium, even under increasing water contents. Moreover, ψ may have approached atmospheric pressure, as Germann and al Hagrey () reported from the Kiel sand tank during infiltration. In conclusion, there was no impact of antecedent ψ on early infiltration whereas water moved freely.…”