Evaluation of different methods for the determination of saturated hydraulic conductivity for simulation of water table depth and drainage discharge using the DRAINMOD computer simulation model

The purpose of this study was to investigate application of the DRAINMOD computer simulation model for estimation of water table depth (W) and drainage discharge (q) by using different values of saturated hydraulic conductivity (Kₛ) in a subsurface drainage system in Kooshkak area in Fars province. These values of Kₛ were obtained from the drainage system, a direct measurement of Kₛ calculated from drainage data (Kₛ₁), Porchet method with saturated inverse hole (Kₛ₂), ordinary Porchet method (Kₛ₃) and saturated Porchet obtained using an empirical equation presented by Sepaskhah and Rezaee (Kₛ₄) (Sepaskhah AR, Rezaee A. 1998. Hydraulic conductivity measurement for subsurface drainage system. Iran Agr Res. 17:139–150). The results indicated that saturated Porchet and saturated Porchet calculated using Equation (17) are reliable for determination of Kₛ because their values are close to that obtained from the direct method. Furthermore, the results indicated that W fluctuations and q are estimated properly by the DRAINMOD model, as shown by an index of agreement of 0.90–1.0 and 0.99 for W and q, respectively. However, q estimations were more accurate than W fluctuations, as shown by a mean absolute error of 0.045–0.243 and 1.73–25.44 for q and W, respectively. Using different values of Kₛ in the model caused tangible differences between the results, especially in W fluctuations, and showed that the model is sensitive to this parameter. Among the indirect methods of Kₛ determination, using the measured Kₛ obtained by the saturated Porchet method (Kₛ₂) resulted in more accurate W and q. It was determined that the saturated Porchet method is more difficult and time-consuming than the ordinary Porchet method. Therefore, a relationship between these two tests has been developed in the study area [similar to the equation that was presented by Sepaskhah and Rezaee (1998)] and estimation of Kₛ from ordinary Porchet method can then be converted to saturated Porchet method for use in DRAINMOD model.