Evaluation On The Groundwater Vulnerability In Yinchuan Plain

Groundwater has been playing an important role in people's life and yielding. There are 2/3 cities depending on it to supply their people in our country and the number has been 80% in the northern place. Groundwater's protection includes not only the facet of reasonable use by human being, but also the facet to guard against the pollutant's infiltration. The concept of groundwater vulnerability has been enlarged by many scientists of the world since 1968 when it is first defined by Margat in his articles.Yinchuan plain, which the Yellow River runs through along the east, is the main agricultural area in NingXia hui autonomous region. With the development of industry and agriculture, and also the quantity of the yellow river decreases year by year, groundwater has been as a main water resource in this plain. According to the geology papers about this area, there have two types aquiferous constructions, they are the single shallow groundwater layer and multi-layers. The confined and unconfined water layers are main composed of massive-sandstone and gravel. According to the analysis of water chemical data, the shallow groundwater shows signs of contamination from a wide variety of non-point pollute, this is main relative to agriculture events. In order to explain the groundwater vulnerability in Yinchuan plain, a model, which will calculates the index of groundwater vulnerability, will be constructed with the parametic-system method in this study and depends on the MatLab programe to draw the groundwater vulnerability picture. The model takes into account seven environmental factors, these include Depth to Water, Net Recharge, Types of Aquifer Media, Aquifer Infiltration, Organic Content of Soil, The Vadose Zone Media and the exploitation quantity in shallow groundwater. The index of groundwater vulnerability is a kind of integration for these environmental factors, seven weights will be calculated with the AHP method to indicate the comparatively importance among these factors. A groundwater vulnerability map is created on a 1:250000 scale geographic map depending on the index of groundwater vulnerability.The conclusion of groundwater vulnerability indicates that the highest potential sites for contamination mainly appear in QingTongxia City and parts of place in YongNing County, for reasons of the higher strengthen of precipitation, the shallower depth to water and the suitable aquiferous media for infiltration. From the whole Yinchuan plain to see the distribution of groundwater vulnerability, in the north place of this area mainly appears moderate vulnerability for contamination of groundwater, the higher potential parts distribute in the south place of this area, the lower potential sites for contamination distribute in both east and west, and the Susceptibility Index in the central place is little more higher than in the north place. This kind of distribution characteristic mainly depends on its geology, hydrogeology, and also the situation of land use in Yinchuan plain. The resultant is good coincide with the consistence contour map of NO₃^-(count with N) which was drawn with the data monitored in June 2003. So in some extent, the result of groundwater vulnerability has objectively reflected the whole characteristic in Yinchuan plain.