A Study On Groundwater Flow Systems In The Wudunao Watershed

Ordos Basin is rich in energy and mineral resources and is an important energy base. On one hand, with the development of western strategy, more water resources are required. On the other hand, the area is located in the arid and semi-arid region, short of surface water. Pumping groundwater is a common practice. However, it have resulted in a series of problems, such as the lower groundwater level, reducing water resources, declining water quality, lakes shrinking, vegetation degradation and soil desertification. So it is urgent that researching the formation and evolution of regional groundwater flow actively and utilizing groundwater resources sustainably.T?th(1963) founded the theory of regional groundwater flow, and many scholars made it better now. In this paper, Wudunao watershed, the Ordos Cretaceous Basin typical small catchment, was selected as a study area. Spatial distributions of groundwater dynamic, chemical and isotopic characteristics in the area were discussed on a small watershed scale under the guidance of the regional groundwater flow theory.The correlation between phreatic level and the elevation is very good, so it is believed that the phreatic level is the topographic controlled in the study area. The range of the discharge area is replaced approximately with the artesian area divided.TDS, Cl, SO4, Cl/HCO3, Na and Na/Ca increase gradually from the recharge area to the discharge area, while HCO3 and Ca reduced gradually. The hydrochemical type is Ca-HCO3 in the recharge areas, and that is Na-HCO3 and Na-HCO3·Cl in discharge area. The δD and 18 O of the recharge area was larger than those in discharge area, indicating experiencing the evaporation. Groundwater age of the recharge area is younger than those in discharge area through Tritium.The hydrochemical type of middle groundwater in discharge area is Na-HCO3 and Na-HCO3·Cl, and that of shallow water is Ca-HCO3. The δD and 18 O in middle groundwater is smaller than the shallow one, indicating that the shallow groundwater was evaporated. TDS and other basic ions in DK2 hole in discharge area show vertical zonation, which considers that different groundwater flow systems result in different water chemical and isotopic characteristics.Finally, groundwater model of the typical cross-section is simulated using the constant head boundary. An internal stagnation point is found below the reverse groundwater flow system in Wudunao watershed. Three local flow systems and a regional flow system were divided by stagnation point. Groundwater chemical and isotopic vertical zonation in DK2 can be explained by DK2 hole just through the three water systems. It is also found that the greater the anisotropy ratio, the closer stagnation point to the surface, and the less local flow system.