Water and salt balance studies, using SaltMod, to improve subsurface drainage design in the Konya–Çumra Plain, Turkey

Soil salinity and water logging are unavoidable processes in areas under excessive use of ground water and poor irrigation management. This study was undertaken to simulate the effect of different drain depths on the amount of drainage water, root zone salinity, and depth of water table in the Konya–Çumra Plain, Turkey. SaltMod model was tested with data collected from the Karkın pilot area. Effects of current irrigation–drainage practices on root zone salinity and drain discharge rate were evaluated. Data such as drain discharge, soil salinity, water table depth, and soil properties were collected. The soil salinity was not high in the test area, but there were commonly high water table and high salinity in the plain. The average soil salinity in the root zone decreased from 2.90 to 2.3 dS m−1 at the end of 4 year period. Simulation results indicated that the leaching efficiency is 0.7 and natural drainage is 0.120 m/year in the test area. When drain depth is considered to be as 1.20 m, 80% of the soils would have a salinity with electrical conductivity (EC) less than 2.72 and 2.71 dS m−1 for the first and second seasons, at the end of 10 year period. The drain depth in the test area was about 1.5 m. However, the assumed depth of 1.2 m appeared to be feasible.