Effect of Land Use Change on Spatial Variability of Infiltration Parameters

Spatial variability of infiltration has an important role on the hydrological processes. Spatial variability of infiltration is affected by extrinsic and intrinsic properties of soils. The objective of this study was to investigate the spatial variations of infiltration parameters through the variation of soil intrinsic properties and land use variation (as an extrinsic factors) using geostatistics methods. Therefore، 95 single ring infiltration data were measured from a field with rangeland and degraded rangeland land uses، simultaneously. The parameters of the Philip model were then obtained using measured infiltration data for all sampling points. The spatial variations of the parameters were assessed using the whole measured data and measured data at rangeland land use، separately. The mean infiltration data in the rangeland land use were higher than the degraded rangeland. It seems that cultivation activities that led to degrading in the rangeland are one of the reasons for decreasing the infiltration at the degraded rangeland comparing to protected rangeland. The geostatistical analysis indicated that strong spatial variability in Philip parameters exist in the investigated area، such that about 10 percent of saturated hydraulic conductivity variation and 35 percent of the variation in sorptivity parameters was random in the rangelands. The variography of the parameters showed that the land use change affected saturated hydraulic conductivity parameter more than sorptivity parameter، so that results on decreasing the spatial structure of saturated hydraulic conductivity and sorptivity parameters from 89 and 64 percents to 56 and 53 percents، respectively. The comparison between the result of this study and the past study showed that the spatial variability of hydraulic conductivity depend on the study area. The results indicated that the geostatistics method was a proper method for predicting the infiltration parameters in the study area with 0. 08 and 0. 19 RMSE for saturated hydraulic conductivity and sorptivity، respectively.