A Guide to Drainage
COMPACTION and INFILTRATION DRAINAGE to LOWER WATER TABLE
Compaction combined with smearing of the surface particularly on winter games pitches , without proper maintenance will render even the best drainage system pretty ineffective .
That ’ s why we often hear ‘ we put a drainage system in three years ago and it ’ s stopped working ’! Perhaps it ’ s the maintenance that needs looking at .
WATER TABLE
In drained land the level of the water table is controlled by the depth and spacing of the drains . They can either be deep and widely spaced , or shallower and more closely spaced to achieve a similar result .
DRAIN SPACING / DEPTH and WATER TABLE
The actual depth and spacing can be determined by calculation but the principle of which route you take will depend upon how quickly water needs to be drained , and how stable the soil needs to be at depth . There is clearly a cost implication too as more intensive systems will cost more .
It can be seen that a water table is formed in soil at the top of the saturated zone where all the pores are filled with water . Above this is the unsaturated zone of soil where the pores contain air as well as water . The level of the water table can vary . If it is at the soil surface you have a waterlogged soil , if is above the surface you have a flood !
To support plant growth the water table must be maintained below root level to give plants aerated soil conditions . The purpose of drainage is to control the level of the water table .
For example agricultural drainage generally favours deep and wide spacing . Drainage is slower but provided the land dries out within a day or two after rainfall , i . e . the water table is lowered below the rootzone , plants like corn and grassland will not suffer too much in 24 to 48 hours . The drains are deep to create a low water table so that the soil is more stable at a greater depth to support heavy agricultural machinery like tractors hauling heavy trailers and harvesting machinery like combines which can compact the soil and damage soil structure in wet conditions , and damage drains if they are too shallow . So agricultural drains will often be about 1 metre deep and 20 , 30 , or even 40 metres apart . www . footballfocus . biz 9