Saturated hydraulic conductivity (Ks) is an important parameter influencing subsurface drainage design and performance, and Ks can be affected by subsurface drain installation methods. Ks was measured at a field site at Nashua, Iowa, with 1.2-m (4-ft) deep drain lines installed with a trenchless plow and with a chain trencher at four depths [0 to 150, 150 to 450, 450 to 750, 750 to 1000 mm (0 to 6, 6 to 18, 18 to 30, 30 to 40 in.)] using the Guelph permeameter (in situ technique) and the constant head permeameter method (laboratory technique) on undisturbed soil cores which were removed from the field site. Ks values were 10 to 130 times greater for the constant head permeameter compared to the Guelph permeameter method and were significantly different at all depths for the two measurement methods. The laboratory technique yielded greater standard deviation values for all depths, whereas the coefficient of variation values were greater for the in situ technique. Drain line installation methods did not significantly affect Ks at the 0 to 150 and 150 to 450 mm (0 to 6 and 6 to 18 in.) depths; however, at the 450 to 750 and 750 to 1000 mm (18 to 30 and 30 to 40 in.) depths, the trencher installation method had Ks values two to three times greater than the trenchless installation method and these differences were significantly different. Subsurface drain line installation method can affect the Ks values particularly near the drain line depths; however, these affects did not affect drainage system performance 10 years after installation.
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