Sustainable irrigation in the Yanqi Basin, China

The Yanqi basin, located in Xinjiang Province, China is a typical example of an area suffering from soil salinization induced by irrigation. The application of stream water without adequate drainage has raised the groundwater table in recent years, causing significantly increased groundwater evaporation (phreatic evaporation) and triggering soil salinization. The Yanqi basin has abundant groundwater resources recharged by the rivers outside the irrigated area. Groundwater from the second aquifer layer could be used for irrigation purposes as the water quality is high. If a part of the irrigation water directly drawn from the rivers is substituted by river water pumped indirectly from the aquifer, the groundwater table will drop and the process of salinization will be slowed down. However, abstraction from the second layer does include a risk. If the groundwater table in the first layer is lowered due to the abstraction of water in the second layer, water infiltrating from the (saline) first layer to the second layer continuously imports salt into the second aquifer layer. A coupled model of ground and surface water flow was set up to determine the resulting salt concentration of the aquifer system as well as of the irrigation water. Moreover, the ideal amount of groundwater applied to irrigation was determined by using the model. The model was constructed and verified by using spatially distributed input data derived from remote sensing. The simulations revealed that around 50% of the phreatic evaporation is related to irrigation. Moreover, the simulations showed that for every m3 of groundwater pumped, phreatic evaporation is lowered by 0.75 m3, and that the salinized area is reduced by 50 km2. Besides showing the changes in the overall water balance, the simulations proved that the steady state salt concentration in the aquifer system and in the irrigation water remains low, even if groundwater from the second layer is abstracted.

, 2015