Sensitivity Analysis of Hydraulic Parameters in the Simulation of Unsaturated Soil Water Dynamics

Soil water content is one of the most important parameters for estimating irrigation frequency and providing the plant's water requirement. since measurement of soil water content is both expensive and time consuming, water movement models are used toestimate these values . in this study, leachw model was used to estimate soil water content for two dry (20-29 aug) and wet (1-6 jul ) periods during the 1995 growing seas on. different values of hydraulic parameters were applied to investigate the sensitivity analysis ofthese parameters in the estimation of soil water content. thus the values of b (pore distribution coefficient in campbell ' s equation (2) were selected from 2 to 24, and k()/k s ratios of 0.1, 1, 10 and 100 were used . finall y 32 treatment s were investigated for each period . results showed that desp ite larg e varia tion for the hydrauli c parameters, similar trends of result s were obtained for all soil water content estimations. stati stical analysis comparing the estimated and measuredresult s showed a sys tematic di fference whi ch can be adju sted using a few measured valu es of soil moistures. as an example, simulated results using b=24 and k())/ k, =0.1 were calibrated to adj ust the simulated result s. the result s o f this study showed that a simple calibration method can be used for the estimation of soi l moisture content without using extensi ve data requi red to repr esent hydrauli c characteristics of soils .