Located in the extremely arid region, Tarim River is the longest continental river in the northwest of China where the environment is vulnerable. Since the construction of Daxihaizi Reservoir in 1970's, the river channel in the lower reaches of Tarim River with 321km distances from the Daxihaizi Reservoir to Tatema Lake has been dried up for more than thirty years. Cut-off of river water along the lower Tarim River and the excessive and unbridled utilization of water resources resulted in a series of ecological environment problems such as groundwater level decline, natural vegetation deterioration, desertification acceleration and so on, which has been accelerating environmental degradation and strongly influenced local agricultural development. In order to conserve the natural vegetation and further to control the desertification and restore the severely degraded ecosystem, an emergency plan-the ecological water conveyance project (EWCP) for synthetically harnessing deteriorate ecological environment were implemented in the lower Tarim River since 2000. After 12 times of ecological water conveyance (The deadline is January 2011), the groundwater level showed some degree of raising along the main river channel of the lower reaches of Tarim River.
Groundwater level has played a key role in the degraded natural vegetation restoration due to the natural vegetation growth mostly depended on groundwater in extremely arid region. Ecological water requirement in the river channel along the lower Tarim river was highly related to elevation of the groundwater level while the elevation of groundwater level is supplemented from the EWCP. To estimate the requirement of the ecological water, firstly two main river along lower Tarim River channels were set up, including the new river channel from Daxihaizi reservoir to Taitema Lake and the old river channel from Daxihaizi reservoir to Alagan, then to analyze the response range of groundwater level to the ecological water conveyance and evaluate the ecological water requirement based on the groundwater restoration by investigating the response width of groundwater restoration after the ecological water conveyance. The phreatic evaporation method was applied to analyze the ecological water requirement in virtue of the Remote Sensing and GIS techniques. The results showed that: (1) The range of groundwater level change was positively related with the amount of water transferring to the channel in the Lower Tarim River. It was charactered by a temporal hysteresis with the response of the groundwater level to the amount of watering to the river channel. The groundwater level decreased obviously from 2004 to 2010, and that was in a negative equilibrium state. The response range of the groundwater to water transfer was 1195 metres, 1050 metres, 2281 metres, and 1000 metres in the transections of Yusu, Kaerdayi, Alagan, and Yiganbujima respectively. (2) After 12 times (for 11 years) of ecological water conveyance in the lower reaches of Tarim River, the total amount of water requirement based on the groundwater restoration was 7.06×10⁸ m³, including 4.98×10⁸ m³ from Daxihaizi reservoir to Taitema Lake and 2.09×10⁸ m³ from Daxihaizi reservoir to Alagan transaction. And it needs about 5 to 8 years that the groundwater depth elevate to 4.5m (equal to ecological groundwater level).(3) The amount of ecological water requirement for the natural vegetation protection is 0.587×10⁸ m³ to meet up with the requirement of the total area of 96114.09 hm² of natural vegetation strip from Daxihai reservoir to Taitema Lake. Moreover, the amount of ecological water requirement is 0.21×10⁸ m³ for the natural vegetation protection zone of 41439.85 hm² in the area of the groundwater level responding to the ecological water conveyance.