Modeling Groundwater Table Dynamics at the Lower Reaches of the Tarim River

The Tarim River is a typical inland river.Riparian plants along the bank of this river mainly depend on the flood and groundwater to maintain their growth.The groundwater table depth determines the establishment,survival and growth of these plants.Since 2000,continuous monitoring of groundwater has been carried out by Tarim River Management Bureau and Xinjiang Institute of Ecology and Geography,Chinese Academy of Science.Observation wells were set up along the cross sections perpendicular to the riverbed,and some pertinent researches and analyses have been done(Chen et al.,2003,Deng,2005).Due to the limitation in the number of the observation wells,examining groundwater spatial distribution is of significance,which will play a more dominant role in rational evaluation and scientific ecosystem management in the lower reaches of Tarim River.In this paper,the groundwater flow and the water-table fluctuation during the past 3 years(2001-2003,964day) were simulated to obtain the spatial and temporal distribution of groundwater table by means of the GIS-based FEFLOW modeling based on the Digital Elevation Model data(DEM,5m precision) and hydrogeologic data obtained in the Alagan section,one representative section of 12 groundwater-monitoring sections,in the lower reaches of Tarim River.The hydraulic conductivities around the study area vary from 0.25 to 0.28×10~(-4)m/s and specific yield ranges from 0.15 to 0.26.Considering the aspects of the large area and the small horizontal head drop(1/10062),the depth of the phreatic aquifer is determined 29.7m and the elevation of the bottom barrier of the phreatic aquifer in the simulation area is a fixed value(782.09 m),i.e.the value subtracted 29.7m from the elevation at the lowest place in the study area.The groundwater recharge from precipitation and condensed water was omitted and the groundwater discharge from evapotranspiration and evaporation also can be neglected when the groundwater depth is deeper than 4.5 m.In terms of river data,combining TauDEM(Terrain Analysis Using Digital Elevation Models) for extracting and representing steam network with the '1D linear interpolation along lines' method in Feflow can obtain the water level data along the whole river.The model can be applied with relatively limited data to simulate the dynamic change of groundwater table.Then the calculated groundwater table can be used to analyze the relationship between groundwater and vegetation.The results of the modeling showed that groundwater was affected mainly by recharge from the river leakage,main effective region of this recharge was 1.0 km from the river and within this effective region the groundwater depth was below 9 m.