Effect of spatial variability of surface soil saturated hydraulic conductivity on water drainage at field scale

Abstract

The objective of this paper is to evaluate the effect of spatial variability of the surface soil saturated hydraulic conductivity(Ks) on water drainage. A conditional simulation (CS) method was used to get a random field of the surface soil Ks based on 117 observed values in the field. Then, a soil water movement model (HYDRUS-1D) was coupled with the random field of the surface soil Ks. During the period from March 10 to June 10, 1999, water drainage was stochastically simulated with the total water income being 353.8 mm(including 270mm irrigation rate). The accumulated quantities of the water drainage ranged from 23.73 mm to 64.73 mm in the soil profile 2 m in depth, accounting for about 8.8% and 24.0% of the irrigation rate during this period. The accumulated quantities of the water drainage were calculated by measured method, ordinary Kriging(OK) method and CS method, respectively. Their results were compared. It was found that the accumulated quantities of the water drainage obtained by CS method agreed well with that by the measured method, while the water drainage range was shortened by the OK method because of its obviously 'smoothing effect'. The effect of spatial variability of the surface soil Ks on water drainage could be reflected by the three methods and their results were all better than the traditional method, which does not consider the spatial variability of the surface soil Ks.