The Interrelationship between Irrigation, Drainage and the Environment

The intended effect of irrigation, a human intervention, on the natural environment is twofold: (i) it changes the land surface and the hydrology of the irrigated area; (ii) it affects the soil moisture-solute-groundwater regime of the irrigated area: water and solutes that would not be present naturally are brought to the area by means of canals. Two important non-intended consequences within the irrigated area are the risk of waterlogging and the risk of salinization. Waterlogging occurs when more water is entering the area than is discharged. The groundwater table will rise, and eventually can approach the soil surface, thereby rendering the topsoil unsuitable for root growth. Salinization occurs when more salts are entering the area than are leaving the area. Downstream of the irrigated area two further consequences are: the decreased river discharge, and the return flow of polluted water (both agricultural and urban).