Research On Groundwater Recharge In Luanjing Irrigation Area, Inner Mongolia

Luanjing, located in Inner Mongolia, northwest China, is an ecologically fragile area, characterized by low and irregular rainfall, high evaporation, and notable drought periods. Since the establishment of irrigation area in 1994, Water has been diverted from the Yellow River and irrigation water infiltration has been the primary source of groundwater recharge. There is misuse and wastage of water resources with traditional flooding irrigation. Excessive water may also produce high mineralization of aquifer and water table rising, leading to soil secondary salinization in low lands.It has a great theoretical and practical significance to choose the reliable method for evaluating groundwater recharge accurately and revealing the temporal and spatial change law of groundwater recharge, which is propitious to provide a scientific basis for water resources management and sustainable use. At present, there are many evaluation methods for groundwater recharge, and different evaluation methods are applicable to different spatial and temporal scales, scope and reliability. So it is very important to choose the appropriate method according to the research.The study was carried out in Luanjing basin, an arid area with deep aquifer, Inner Mongolia. In the research, soil water balance method, chloride profile method and groundwater level fluctuation method are used to describe the groundwater recharge in Luanjing Irrigation Area, where the utilization of irrigation water is very low. Leakage in different stratum and different crops are estimated by soil water balance method, which indicates that the irrigation leakage amount is contacted with the irrigation norm, soil moisture content before irrigation, soil texture and planting crops. For example, in the land cropped with corn, the average leakage for six irrigation times in dual-layer stratum is 251mm, which is larger than 81.9mm in the multi-layer stratum cropped with oil heliotrope. Chloride profile method is also applied to estimate the annual groundwater recharge in natural and long-term irrigation sites, showing that direct recharge by rainfall is less than 0.1 mm/a, and the irrigation infiltration recharge in long-term irrigation sites is 231.5mm/a, which is consistent with the results using soil water balance method. The water table observation data shows an about 1m increase of groundwater level from December 2005 to September 2008, which reflects the influence of traditional flooding irrigation on groundwater.By analyzing application of different methods in Luanjing Irrigation Area, the application condition, limitation and accuracy of each method are discussed. Recharge estimated by soil water balance method and chloride profile method are reliabe, and the accuracy of groundwater fluctuation method is low due to deep aquifer, small density of observation wells and groundwater runoff.Finally, the paper provides some control measures of groundwater levels in response to the local utilization situation of groundwater. Such as modifying irrigation norms and improving irrigation technique, optimizing plant structure and implementing water-saving irrigation system, strengthening the water conservancy project measures and agro-ecological measures, and so on.