Drainage involves the removal of excess water from the root zone when a permeable root zone is placed above an impermeable subsoil. Rapid drainage of excess surface water is important in ensuring the maximum use potential for the turfgrass area. Drainage functions in washing soluble salt out of the rootzone and prevents salt accumulation to potentially toxic levels in arid regions. Air is also drawn downward from the aboveground atmosphere as the excess soil water percolates through the soil, thus enhancing soil aeration.
People have assumed that if sub-soil drains are installed in certain locations that water will quite “logically” flow into them through the soil. Some textbooks even tell us this. Once again it is often wrong, simply because the first assumption that ‘water flowed sideways in the soil at a reasonable rate’ was in itself wrong.
Because of these circumstances, teachers, students and people in the industry make incorrect assumptions. The incorrect assumption that occurs most frequently is that water will move sideways in soil at reasonable rate. One may reasonably ask “well, why wouldn’t it?” It does seem logical, but in fact it is wrong.
Water moves sideways in soil extremely slowly, and for all intents and purposes the significance of this movement can be ignored in most situations. If this initial incorrect assumption has been made, ‘that water will indeed move sideways in soil at a reasonable rate’, then the decisions that follow based on this assumption, often have quite serious and expensive consequences.
On the basis of this incorrect assumption, we see millions of dollars being spent all around the world by people installing sub-soil drains in playing fields, golf courses, race courses, garden beds and various other places. Unfortunately these will never drain anything effectively other than area directly above the drain pipe itself, and perhaps with time, a total width of about a metre if the soil profile is deep enough.
The behavior of soil can be predicted by carrying out laboratory tests such as particle size analysis and hydraulic conductivity at various compaction levels. This can give you a very good idea of how soil will behave in certain situations in the field. This professional approach should be essential to ensure that a new facility will perform in the way that it was intended.
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