Effective Hydraulic Conductivity for a Soil of Variable Pore Size with Depth
Two models were derived for the estimation of effective hydraulic conductivity (Ke) of a soil layer based on exponential and inverse square variation of hydraulic conductivity with soil depth. Darcy’s law was applied to a vertical soil stratum subdivided into a finite number of layers. The relationship between Ke and layer thickness is of quadratic form with R2 ≈ 1.As the layer thickness increases, the values of Ke for the exponential model increases drastically, exceeding the Ke estimate of the power model. The percentage difference between the two models assumes an asymptotic form to the y-axis at a percentage difference of 5%, as the size of layer approaches zero. power model gives lower estimates of Ke than the exponential model within soil depth range of 1.5m ≤ D ≤ 3.2m for n = 2; 0.8m ≤ D ≤ 1.9m for n = 50; and 0.7m ≤ D ≤ 1.9m for n = 100 and above. For very shallow soil stratum (D ≤ 2), the exponential model gives better and more realistic estimates of Ke than the power model; while for medium to deep soil stratum (D ≥ 2), the power model gives better estimates of Ke.