DESIGN OF A SENSITIVE AND PRACTICAL CONSTANT HEAD WELL PERMEAMETER

We designed a three-piece constant head well permeameter (DCHWP) consisting of a burette reservoir, a detachable water transfer tube, and an outlet tube. It measured in situ field-saturated hydraulic conductivity (K(o)), flux potential (phim), and sorptivity above the water table accurately in a series of field tests carried out in sandy, loamy sand, and sandy loam soils. The sensitivity of the designed permeameter is 0.25 mm. It is cheap, and its components are easily available. Its working range over the K(o) measurement (1.1 x 10(-8) ms-1 less-than-or-equal-to K(o) less-than-or-equal-to 7.7 x 10(-5) ms-1) and over the depth profiling (0.05m less-than-or-equal-to D less-than-or-equal-to 4.0m) is quite large so that it can be used in different soils of widely varying K(o). Its water requirement (2.0-2.25 liters) and time requirement (20-30 min) are low, in practical range. It presents minimum operational problems. The DCHWP method consistently gave results similar to the double-ring infiltrometer method. Averaging for three soils, the inverse auger hole method overestimated K(o) by 50%, and the soil core permeameter method underestimated it by 48%. The K(o) and phim values were not significantly affected by height of water in the well or radius of the well.