Document Type : Research Paper
Assistant Professor, Agricultural Engineering Research Institute, Iran
Graduated M.Sc. of Irrigation and Drainage Engineering, Ferdosi University of Mashhad, Mashhad, Iran
M.Sc. of Irrigation and Drainage Engineering, Saman Abrah Consulting Engineers, Iran
Today, in drainage projects under construction in Iran and especially in Khuzestan province, the huge part of costs allocated to preparing mineral envelope (gravelly) for subsurface drain pipes. In other hands, by soil characteristics of some areas and in base of technical recommendations, drainage performance without using envelope may also be an option. So, in this research and as one of the first experiments in real scales in Iran, through an experimental field with 20ha area and by wheat planting, subsurface drainage without using envelope (in considering the local soil characteristics), excess than conventional drainage by mineral envelopes, was performed in Shadegan region of Khuzestan province. Each experimental unit contains 5 laterals (subsurface drain pipes) by distance of 50m and drain depth and length of 1.7m and 220m, respectively. For study of water table condition, some piezometers with a depth of 2m were installed perpendicularly to laterals of each unit, around the middle one at distances of 0.5, 2.5, 5, 10 and 25m from drain pipe and manholes prepared for these laterals. Also, in a distance of 30m from the beginning and the end of the middle drain, 2 more piezometers with distance of 0.5 and 2.5m from it were installed. Drainage with mineral envelope performed in 2 units, but drainage without envelope only done in one unit, via to prevention of farmers (but data were collected from 3 middle drains in this unit). Investigation of water table depths indicated that the operation of drains without envelope were acceptable and for mineral ones were proper during an agricultural season. Calculation of Relative Ground Water Depth index (RGWD) showed that subsurface drains without envelope had acceptable operation during this research in Shadegan drainage plan area and with low sedimentation in manhole. Therefore, if proper operation happens in middle time and long time periods, it could be propounded as a practical option in areas same as Shadegan region.