Traditionally, subsurface drainage systems with drain depths of 1.75 m or more and drain spacing more than 50 m were implemented in other parts of Iran.
Drainage treatments were: three conventional subsurface drainage systems including drainage system with drain depth of 0.9 m and drain spacing of 30 m ([D.sub.0.9][L.sub.30]), drain depth of 0.65 m and drain spacing of 30 m ([D.sub.0.65][L.sub.30]), and drain depth of 0.65 m and drain spacing of 15 m ([D.sub.0.65][L.sub.15]); a bi-level subsurface drainage system with drain spacing of 15 m and drain depths of 0.65 and 0.9 m as alternate depths (Bi-level), and surface drainage system with drain depth of 1.2 m (Control).PVC corrugated pipes with an outside diameter of 100 mm were used as lateral drains.
The approach flow head loss is affected by the physical properties of this disturbed soil which surrounds the drain, the
drain spacing and the drainage materials used.
In permeable soils where drain spacing is wide, a system of open ditches can be used in lieu of pipes.
In the design of WTM systems used solely for drainage, both the depth of the drain and the drain spacing must be specified.
Agricultural profits for this alternative are reduced because shallow drains require closer drain spacing, which increases costs.
Annual corn yields and nitrogen losses were predicted for a 40-year period using the model DRAINMOD for a range of drain spacings and depths.
Trade studies can be performed with this notebook to observe the effect of FET cell size or the effects of the source and
drain spacing on junction temperature with the ultimate goal of keeping the FET junction temperature as low as possible.
This can be achieved by increasing drainage layer thickness or decreasing drainage length (closer strip
drain spacing).
* Even using a close
drain spacing, it is unlikely that significant depressurisation of the bedrock would have been possible; recharge from the overlying alluvium would have occurred at a rate which was greater than the capacity of the drains
The threshold
drain spacing for each criterion was determined from Figure 5.
The design of the seepage drainage is a continuous operation regime, by establishing the pose depth, the length of the drain, the
drain spacing and after that checking the drain in non-permanent function.
