Prediction of water table dynamics between bi-level subsurface drains in paddy fields

Implementation of subsurface drainage in Northern Iran paddy fields is crucial to achieve the feasibility of round-cropping and improve sustainable use of limited soil and water resources. One of the subsurface drainage systems is bi-level system that can be installed because of lower costs than conventional and better control in drains discharge. Installation of this system needs suitable knowledge of designing of subsurface drainage systems due to layered soil of paddy fields. In this study¡ an analytical solution of two dimensional transient saturated flow of Bear equation to subsurface drainage in a paddy field is presented to investigate the bi-level drainage systems operation. Also¡ due to importance of vertical head in clay and layered soils¡ a modified procedure was performed to separately involve vertical head. Validity of the solution has been evaluated by comparing with the field data collected at paddy fields of Northern Iran. The two dimensional solution was not able to reasonably predict the water table profile. But the obtained results indicated that considering the vertical resistance in the media improved the simulated data in the bi-level subsurface drainage systems and provided good representation of water table dynamics. The differences between field data and results were only 21% for modified procedure in comparison with 61% for two dimensional solution. Totally¡ it would be mentioned that in future work for designing bi-level drainage systems in paddy fields¡ the vertical head loss should be considered.