Risk Analysis Of Vegetation Affected By Groundwater Development In Taoli Watersource Area In Odors Basin

The vegetation is fragile in arid and semiarid area in the northwest of China, and it closely correlates the depth to groundwater surface. Exploiting groundwater unreasonably will lead to the groundwater level descending irrationally in this field, and it will deteriorate and desert the vegetation eco-environment.Taoli watersource area is located at the Desert Maowuso, the arid-semiarid area in the northwest of China. Groundwater is very important to the water supply in this area. Vegetation in this field is also fragile and much of it is closely related to the groundwater depth. As a result, to carry out large-scale exploitation of water sources, risks will be caused by the underground water level dropping. So the factors of vegetation should be taken into account when assessing and planning groundwater resources in the field. This paper, based on the item"Investigate of Groundwater in Taoli Wellworks in Ordos Basin", studied the risk of vegetation under the condition of groundwater withdraw in Taoli which located in the centern of the Maowuso Desert. This article used the data of vegetation investation to study the coverage, richness and dominance of this field, and then to identify the predominant species of vegetation. The most dominant species of vegetation was artemisia, carex, salix psammophila. The frequency of dominant species under different water level could be employed to work out five intervals of ecological water level such as water level of salinization, reasonable water level, restricted water level, languish water level and dangerous water level.The main salt-tolerant vegetation that grew at the area whose water level was in range of 0.5m to 1.5m what is the range of the water level of salinization. The best survival water depth was between 1.5 m and 3.0m, within the range all the plants could develop normally and a wide variety of vegetation could grow. The low-humidity vegetation growth would be restricted at the level between 3.0 m and 5.0m which was the range of growth limited water depth, but little effect on the Saudi. Languish water level was between 5.0 m and 8.0m, due to low humidity vegetation degradation, drought and some of the sand vegetation growth restriction, poplar, willow and other trees in a wilting. Dangerous would appear when the water level was more than 8.0 m, only drought-resistant plants such as sand Artemisia and Caragana maintain normal growth.The relationship between coverage and lithology of unsaturated zone, and topography and groundwater depth could be composed with root depth of dominant species to part the vegetation sensitivity zone.The first sensitive area was located at the low-lying beach and the area surrounding Lake dried up, where the main vegetation was low-humidity vegetation. The second sensitive areas in the study area were covered by masses of eolian sand, where drought-resistant vegetation growth in.Distribution of non-sensitive areas in the eastern and western sand beam which was watershed of groundwater, and it was great depth to the water table in these areas. Plant such as artemisia that was not high relevance of the water table was the main vegetation.Groundwater flow numenical simulation model based on the condition of hydrogeology in the field was set up to predict the groundwater drawdown in the next five years with three projects which used c of 100 000m3/d, 80 000m3/d and 60 000m3/d. The result showed that the area of drawdown between 1.5m and 3.0m had been more than 90% of the field after five years.Risk indexes of vegetation ecology had been established on the base of the result of the three projects.And risk zones were also classified according to the indexes.What's more, the high risk zone which was mainly distributed in detailed investigated area would become larger and larger with the augmentation of groundwater withdraw. On the contrary, the area of middle risk and low risk would decrease.High-risk areas were mainly located in the exploitation that caused the groundwater table dropped about from 1.5 to 3m after five years of groundwater resources on the beach areas. Some low-humidity vegetation could not grow normally and even gradually degraded, its original dominant vegetation will be replaced by drought-resistant vegetation. Medium-risk areas were larger than other risk area and were covered by aeolian sand. The main vegetation was Artemisia who was less affected by the decline of water table depth. But some low-humidity vegetation is locatede in the surrounding areas of drought-lakes. The main plants would be replaced by Artemisia with the increased depth of the water table caused by development of groundwater. Low-risk areas in the distribution of watersource to the southwestern and northern regions, for the wind-sand covered areas. The growth of vegetation mainly was Artemisia and Salix psammophila who was dry desert vegetation. Water level drop caused by groundwater exploitation could not generate too much risk to these vegetations. Security zones were located in the east and southwest on the beam. The main vegetation is Artemisia, Caragana and some other drought-tolerant herbaceous plants which is not high degree of dependence on the depth of the groundwater level. The exploitation of its groundwater resources didn't constitute a risk.