Effect of Sample Cross-Sectional Area on Saturated Hydraulic Conductivity in Tow Structured Clay Soils
ABSTRACT SATURATED hydraulic conductivity (K) was measured on two structured clay-rich soils in Ohio using samples with three different cross-sectional areas, 625, 44 and 13 cm2. One of the soils tested had approximately 35 macropores/m2 and the other soil had few or no macropores. The mean vertical saturated hydraulic conductivity of the soil with macropores varied from 20 to over 100 times that of the soil without macropores. Vertical K values were ten times greater than horizontal K values in the soil with macropores. The method employing the largest cross-sectional area resulted in the smallest coefficient of variation in the soil with macropores and fewer large samples than samples with a smaller cross-sectional area were needed to estimate the mean K value within ±20%. The number of samples required depended on the mean K and coefficient of variation of the method tested. The soil with macropores had such a large mean K that, although it had greater absolute variability, fewer samples were required to achieve the same relative degree of precision compared to the soil without macropores. The standard deviations of K for the soil with macropores were 20 to over 70 times those of the soil without macropores.