As shown in the figure, a lower water table and a drier soil layer are obtained by installing the drainage system. This creates physical, chemical, biological and hydrological effects on the soil. These effects are shown in the figure. For example, improvement of the structure increases infiltration. As infiltration increases, surface flow decreases.
The main factors that cause the drainage problem in irrigated areas are:
Loss of water during the introduction and application of irrigation water to the field
Uncontrolled delivery of excess irrigation water to the soil
Foreign waters coming from underground to agricultural areas
Excess rainfall and flood waters
The causes of drainage problems in rainy and arid regions are different.
The main source of the drainage problem in rainy regions is the increase in surface flows and groundwater levels caused by the excess rainfall.
Drainage problem occurs in arid and semi-arid regions by irrigation.