FACTORS AFFECTING FIELD AND LABORATORY MEASUREMENT OF SATURATED HYDRAULIC CONDUCTIVITY

Two widely used measurement techniques of saturated hydraulic conducti vity are the Guelph Permeameter (GP) method and the Constant Head Perm eameter (CHP) method. A study was conducted to investigate variations in saturated hydraulic conductivity as related to two factors which ca n influence GP and CHP results. To begin, the influence of the anteced ent soil water content on the GP measurements was studied Then, the ef fect of the size of the soil core on the laboratory estimates was exam ined. Finally, a comparison between results of the two methods was car ried out. The study was conducted in a sandy clay soil. Experiments wi th the GP produced decreasing estimates of saturated hydraulic conduct ivity with increasing antecedent soil wetness; this result was mainly due to the influence of the soil water content at the time of augering the well on the permeability characteristics of the well wall. Labora tory results were influenced by the size of the soil core. In particul ar, ''large'' cores produced lower and less variable Estimates of satu rated conductivity than ''small'' cores, in which the potential for pr eferential flow increases greatly. On the average, results of the comp arison between the two methods were satisfactory only when GP results obtained in the initially dry soil and laboratory estimates obtained o n large cores were selected.