study of the time variability of saturated hydraulic conductivity

abstract the temperature of water entering the soil or variation in soil temperature has a direct impact on soil hydraulic conductivity via the effect on water viscosity. in this research, the time variability of soil saturated hydraulic conductivity (ks) was studied. the relation between soil temperature and fluid viscosity with hydraulic conductivity were also studied. the necessary experiments were conducted on aboureyhan campus research farm located in pakdasht, 25 km southeast of tehran. 18 holes were digged in a plot and saturated hydraulic conductivity of soils were measured in these holes using inverse hole method. experiments were carried out 12 times from 16-aug-2005 to 14-jun-2006. investigations showed that the lowest value of ks was obtained in winter when the soil and air temperatures are at minimum and by increasing the soil and air temperatures, these values increased too. statistical analysis of experiments indicated that soil or air temperatures can considerably affect the results. using the average of measured ks to design drainage systems showed that neglecting the time variability of ks may result in over or underestimating of drain spacing by 18.9% and 23.3%, respectively. using the average of ks values which was obtained in soil temperature of 16-20 oc had least effect on drain spacing, so it can be used as an average ks to design drain spacing.