Hydraulic conductivity and sorptivity at unsaturated and saturated conditions as related to water infiltration in soils

Year 2020, Volume: 9 Issue: 1, 1 - 9, 01.01.2020

Abdelmonem Mohamed Ahmed Amer

https://doi.org/10.18393/ejss.621759

Abstract

Sorptivity (S) has been defined in terms of the
horizontal infiltration equation. At unsaturated conditions (at a very short
time) S represents “maximum sorption capacity”, but in saturated conditions the
sorption capacity decreases with the time. Over a long time of infiltration,
sorptivity was not studied as a soil water parameter that could be determined. The
purpose of this study is to apply derived equations depending on the
infiltration functions to predict (1) soil water sorptivity (S) at infiltration capacity (unsaturated conditions) and
at basic infiltration rate (I_b) (saturated conditions), (2)
the hydraulic conductivity (Saturated Ks and unsaturated K(θ)) into
capillary-matrix and non-capillary macro pores of soils.  Five alluvial (saline and non-saline clay) and
calcareous soil profiles located in the Nile Delta were
investigated for applying the assumed equations. A decrease in S value was
observed with an increase in soil water content. At steady infiltration rate (I_b),
S decreased from 1.04 to 0.647cm.min^-0.5 (i.e. S decreased by
37.79%) in average in calcareous soils and from 0.537 to 0.251cm.min^-0.5
(53.25%) in alluvial clay soils. The steady S_w parameter was used in
prediction of the hydraulic conductivities and the basic infiltration rate I_b
, whereas, S_w is a
suggested term at steady infiltration rate. The calculated values of I_b
were corresponding to those obtained by infiltration experiment. This confirmed
the significance of steady S_w as a new functional infiltration
parameter. A matching factor u was calculated as a ratio between
predicted I_b and the measured saturated hydraulic
conductivity, Ks. The mean values of u were 0.895, 0.685 and 0.360 for
calcareous, clay and saline clay soils respectively. Unsaturated K(θ) has
been discriminated into saturated macro-pore K(θ)_RDP
and matrix unsaturated K(θ)_h. The
values of K(θ)_RDP
for macro pores remained higher than those for soil matrix pores (K(θ)_h) in the studied soils. The
highest value of K(θ) was
obvious in calcareous soil profiles, while the lowest value was existed in
saline clay soil. In
conclusion, the predicted values of hydraulic conductivities of soil matrix
(capillary) and macro (non-capillary) pores were reasonable and existed in the
normal ranges of the investigated soils, indicating that the proposed equations
are applicable and can be recommended to be used in coarse and fine textured
soils with large scale of different properties.

Keywords

Infiltration functions, soil pores, steady sorptivity, unsaturated hydraulic conductivity

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