Environmental Science & Technology 2014 Vol. 2 224 DERIVING VERTICAL SATURATED HYDRAULIC CONDUCTIVITY OF SOIL USING DOUBLE RING INFILTROMETER INFILTRATION INFORMATIOM Milad Fatehnia, Kamal Tawfiq (Florida State University, Tallahassee. FL, USA) ABSTRACT: Making accurate estimations of saturated hydraulic conductivity ( ܭ ௦ ) in Double Ring Infiltrometer (DRI) test requires considering the effects of soil type, initial water content of the soil, ring depth, and head of ponding on measured infiltration rate. Besides, measuring the effect of rings diameters on calculated infiltration rate enables us to use different sizes of the ring. Smaller rings are preferred due to their lighter weight and fewer water requirements. In this study, by conducting 30 DRI lab experiment, 10 DRI field tests, and 864 simulated DRI tests using finite element program HYDRUS-2D, the effects of these parameters on measured infiltration rates were observed and, based on M5 trees model, a formula was generated to predict the ܭ ௦ of the soil. The accuracy of the equation was later estimated by applying the equation on real DRI test parameters and comparing the predicted ܭ ௦ values with the real values measured by Guelph permeameter in the field. INTRODUCTION In soil science, infiltration rate is considered as a measure of the rate at which soil is able to absorb rainfall or irrigation. Despite the similarity of the units of infiltration rate and hydraulic conductivity of soils, there is a distinct difference between these two quantities. They cannot be directly related unless the hydraulic boundary conditions such as hydraulic gradient and the extent of lateral flow of water are known (ASTM 2009). Accurate in-situ (or field) measurement of ܭ ௌ is essential in various environmental and geotechnical applications such as design of drainage systems; measurement of seepage from canals, reservoirs, detention ponds, or wastewater lagoons. Hence, making a precise measurement for the hydraulic conductivity has a considerable importance. FIGURE 1. Cross-section sketch of the double-ring infiltrometer. Double ring infiltrometers are common test methods for in-situ measurement of the soils infiltration rate. The DRI test has been described by ASTM D3385 and, as illustrated in Fig. 1, consists of two open