Drainage is an important issue because most plants cannot survive waterlogging for more than a short time. Most plants need at least 10% to 15% of the soil pore to be filled with air to survive. Soil becomes waterlogged when its pores fill with water. Once the soil is saturated, root growth in most plants can occur only on the surface. When there is more water than the soil pores can hold, the water will collect on the soil surface and drain by gravity to the lowest point.
Surface drainage is the removal of water that collects on the land surface. Many fields have low spots or depressions where water ponds. Surface drainage techniques such as land leveling, construction of ditches or waterways can allow the water to leave the field rather than causing prolonged wet areas.
Subsurface drainage removes excess water from the soil profile and reduces the watertable below theroot zone. Subsurface drainage is used where surface drainage is not effective. With subsurface drainage, slotted polydrain is installed below the surface, covered with gravel to prevent soil particles from being carried into the drain and to improve the flow of the water.
TG Drains installs subsurface drainage using a laser controlled, purpose built, drainage machine. Both machines are imported from the UK. The 26/15 can cut a trench up to 3.0 metres deep and the 20/15 can cut a trench up to 2.2 metres deep. The digging chain of the machine cuts a trench on the design grade and the drainage pipe is laid with a backfill of gravel in one single operation.
