GIS Assisted Modeling Groundwater Level In Fluctuant Zone Of Lower Reaches Of Heihe River

Water resource is limiting factor of the economic and social development in arid area. Now the competitions of water resource in arid area have arisen out of lots of conflict, which severely influenced the stabilization, safety and development of the area. At the same time, the excessive exploitation of water resources has caused severe deterioration of the eco-environment. In order to assign water resource reasonably and protect the local ecosystem in arid area, it is necessary to assess the distribution and changes of water resources exactly.In this paper, we select the water table fluctuant belt of the lower reaches of Heihe River as a study area. In this area, there is little precipitation. The groundwater level which depends on the river water from middle reaches of Heihe River, determines the distribution of vegetation. In the last decades of years, because of the growth of population, the development of agriculture and industry, the water use has increased in the up and middle reaches of Heihe River, in turn a lot of problems has occurred in our study area, such as dried up of the lake, degradation of natural oasis and grassland.Based on the field investigation of geology and hydrogeology and observation data of water resources from 1990 to 1999, combined the GIS technology and the FEFLOW software, the groundwater level was simulated. Using the relationship between the groundwater level and vegetation coverage, the potential distribution of the vegetation was modeled.The main research results are as follows:1. With the assistance of GIS technology, a three-dimensional aquifer system and hydrogeological model was constructed based on a lot of geological data. According to this model, a mathematical model of groundwater flow, which is solved by finite element method with FEFLOW, was established. The groundwater level were modeled and predicted in the study area.2. The main source of groundwater in study area is the infiltration of river water and the drainage mainly results from evaporation of phreatic water. The drainage is far bigger than the source in the whole area.3. From 1990, the groundwater level has declined slowly. The annual variation is influenced due to the water use in up and middle reaches.4. The change of ground water level in year is large actually, some time more than 4 meter a year.5. The vegetation in study area is intimidated by groundwater lever. After building the relationship between the groundwater level and vegetation coverage base on the field investigate, the potential spatial distribution of the representative vegetation is calculated.The results show that, the river water is limitation for the study area; even it is increase in recent year. If water delivery from the middle reaches decreases, the groundwater level has continually declined and the vegetation will not be survival.