Regulation Of Groundwater Pumping Risk In Guanghan City

Guanghan city,known as the back garden of Chengdu City,is located in the northeast of Chengdu City.In general, Guanghan City is abundant of water resources,but the yield of water is reducing than before while some of the water has been polluted.Recently, the groundwater water accounted for 20% of the total water consumption in Guanghan City.There exits the problem of overextraction of ground water in local area,which formates a number of environmental geological problems, such as the water level continued dropping,the groundwater polluted and so on. In order to protecting the groundwater resource and ecological environment, studing on evaluation and regulation of groundwater exploitation risk must be adopted to ensure sustainable utilization of ground water resource and for guiding the rational exploitation and use of the groundwater.The author analysised the geological conditions, hydrogeology condition of the study area, evaluated the risk of groundwater exploitation in Guanghan city by the method of catastrophe evaluation and improving the evaluation results based on domestic and foreign literature analysis, summary of the survey report,field investigation and laboratory test in this thesis. Above on, the study draws the following conclusions:(1) Defining the the definition of the risk of groundwater exploitation and summarizing the concept of groundwater exploitation risk system through the research on the definition of risk while defining the contents, principles and methods of the risk assessment of groundwater exploitation and the index system of groundwater development risk assessment which divided into the target layer, the criterion layer and the single index layer.(2) The method of catastrophe theory is suitable to use as the method of the risk evaluation of groundwater exploitation because the groundwater system is complex and irregular. The theory of catastrophe theory is complicated, but the application of the theory is relatively simple and been used widely. The steps of risk evaluation are as follows: Firstly, normalizing the underlying index;then calculating using the seven evaluation model of basic mutations and mutation evaluation principle step by step,and finally obtaining the comprehensive evaluation value of the total target layer.The catastrophe evaluation method is simple and can be applied to the evaluation of complex system, without any subjective weight while the result of catastrophe evaluation is accurate.(3) Guanghan city terrain from the northwest to the southeast gently inclined, give priority to with plain. It belongs to Dujiangyan irrigated area downstream. The hydrochemical types of groundwater are mainly HCO3-Ca?HCO3·SO4-Ca and HCO3-Ca·Mg. In terms of water quality assessment, the water quality indexes are classified according to the groundwater quality standard GB/T14848-93. The value of pH, Fe, Mn, chloride, ammonia nitrogen, fluoride are defined to class I mainly,the sulfate, nitrate, arsenic are defined to class II, total hardness, dissolved total solids, nitrate are defined to class II or class III. The water quality indicators of nitrate, Fe, Mn,total hardness exceeded in some parts of the study area. In terms of water quantity assessment,the amount of natural resources of groundwater recharge in study area is 19453.169×104m3/a, The amount of recoverable resources of groundwater in study area is 1.65×108m3, the amount of groundwater exploitation is 0.98×108m3;The amount of groundwater resources surplus in study area is 6743.952×104m3/a, This means that the exploitation degree of the groundwater resource is 0.59, a medium moderate degree. The average person possession of water is 845 m3, which belongs to severe water shortage.According to the groundwater enrichment feature,the topography and landform character,the study area was divided into ten regional evaluation.The groundwater exploitation risk size sorting are as follows: ?3<?1<?2<?1<?5<?4<?2<?1<?1<?.The study area is not conducive to the division of grades because of the integrated evaluation results are similar.Therefore,it's necessary to improve the mutation evaluation method. The evaluation results by improved method showed that the risk value of each evaluation area of Guanghan city was between 0.3~0.4 which means that the district of the study area belongs to the light risk level accordings to the previous risk standards. The evaluation value of natural condition of risk are the biggest,while belong to the light level.the evaluation value of development and utilization of risk in area VI 4 is biggest, while belong to the medium level, the evaluation value of social and economic risk in area in II 1, IV 1 are biggest,which belong to light level.