Hydraulic conductivity (K) of the soils is an important parameter in the design of spacing and functioning of subsurface  drainage system . The variability of K value in time and space is often so wide that it becomes difficult to find representative/dependable value. As part of an on going  indo-Dutch Network Operational Research Project on "  Drainage and Water Management for Salinity Control in Canal Commands ",  K measurement studies were carried out at Islampur - Devapur (J) villages, Gulbarga district in Upper Krishna Project command area, Karnataka. The study area consists of black soils (Vertisols) with high clay content underlain by bedded limestone located in canal seepage zone. In situ  K measurements on grid basis by post hole auger method in the Operational Research Project (ORP) area (180 ha)  of the above project were  obtained. They varied from 0.004 to 0.559 m/d and followed the log normal distribution . The geometric mean(GM) of K of the ORP area was 0.07 m /d. The K-contour map was drawn and the vertical as well as radial K values were also computed. For determining the dependable K value, the values were plotted on the normal and log normal probability papers and median values were also considered. It was found that straight line of the best fit obtained with log normal distribution showed log mean of 0.077 m/d. The median value of K (0.083 m/d) was very close to this value.. Therefore, it is concluded that though, log mean could be the more reliable value but median value may be quickly obtained and it is almost nearer to the log mean value. Hence, the median value of  K may be considered for the  designing the subsurface drainage system.