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5. Subsurface drainage
Surface drainage may not be sufficient or practical in poorly drained soils where the water table is naturally near the ground surface. In these cases, perforated plastic pipes are buried in the ground to remove the excess water and lower the water table. This practice is referred to as subsurface (tile) drainage (Figure 4).
In subsurface drainage systems, perforated drain pipes can be installed in a targeted or parallel layout (Figure 5) with the latter being the more common layout. The herringbone layout is a subset of the parallel layout.
A targeted layout is common in rolling landscapes where surface drainage provides enough drainage for field operations on most of the field except in isolated depressional areas where removal of excess water is needed for uniform field operations (Huffman et al., 2013). If the source of water is a naturally shallow water table, a targeted subsurface layout is suitable.
Blind inlets can drain excess water from depressional areas. They are suitable in places where the source of the excess water is mainly surface runoff. To learn about blind inlets, see Ghane (2022a).