干旱区地下水脆弱性特征及评价方法探讨

GROUNDWATER VULNERABILITY AND ITS ASSESSING METHOD IN THE ARID LAND OF NW CHINA

干旱区地下水脆弱性是地下水系统本身固有的不稳定属性 ,是系统结构、功能状态在人类活动干扰及气侯变化等自然因素作用下具有的敏感性、易变性和弹性的综合反映。可以以河川径流中冰雪融水比重、地表径流入渗占地下水补给比例、地下水补给强度、地表水的引用率等十项指标 (IRRUDQELTS)进行定量评价。通过对塔里木盆地南缘地下水脆弱性评价 ,表明该区属地下水严重脆弱区 ,其中又以民丰县、皮山县为极端脆弱 ,结果与实际情况相符合 ,说明该评价指标体系具有一定的科学性。

The concept of groundwater vulnerability in the arid area is defined on the basis of completely analysis and comparing to that of the humid area. The assessing index of groundwater vulnerability and its weighted value were put forward with integrating use expert decision-making and AHP method. Groundwater vulnerability is the unstable property of the groundwater system, which shows the system structure and quality status vulnerability, variability and rehabilitation to human activity and climatic change. What result in groundwater vulnerability in the arid area are (1) extreme drought and climatic fluctuate, (2) irrational human activity and disturb on water resources-ecology system, (3) frequently, great and diversity natural catastrophe, (4) fragile ecology, and (5) occurrence of several ecotones. The IRRUDQELTS index comprises of ice meltwater ratio to runoff, which is the most important recharge source of groundwater in the arid area of NW China. Groundwater recharge intensity is the proxy of groundwater system resisting to the climatic change and Human activity. Runoff infiltration ratio to groundwater resources reflects the weakness to human activity. Runoff use ratio and groundwater pumping ratio express the extent of water resources to be exploited and the potential for future sustainable development. The evapo-transpiration and its discharge, groundwater quality, water level falldown and spring water reduction indicate the strain extent under the combined impact of climatic change and human activity. All data is calculated in term of weighted value correspond to the importance in stable of groundwater. According to the function of each index in the stability of groundwater the weightiness can be evaluated as 0.14, 0.15, 0.14, 0.12, 0.1, 0.1, 0.11, 0.04, 0.05, 0.05 respectively for the IRRUDQELTS. The vulnerability can be divided into five grates. The calculated results showed that the Minfen county and Pishan County are two extremely groundwater vulnerable region in the South edge of Tarim basin with the value higher than 0.7 in DS. Whilst the groundwater in the Hotan rive system is relatively stable with the value lower than 0.45 in DS. The result also shows groundwater under the desert of south Tarim basin is dramatically fragile.