Water Pollution Assessment And Research Of Quality Evolution Rule In Guanzhong Section Of Weihe River

From the past to the present, Wei River Basin plays an important role in Shaanxi's development. Wei River not only has the functions of water supplying, irrigation, flood discharging; but also has the functions of waste discharging, supplementing groundwater and keeping balance of ecosystem in wetland. However, while economic and social developing in Wei River Basin, the problems such as the deterioration of water environment which is caused by growing water shortage, water pollution and sedimentation in Sanmenxia reservoir has affected the lives of people on both sides, as well as restricted the economic and social development.Wei River is the largest branch of the Yellow River, which concentrates 60% of the population in Shaanxi province, 53% of the arable land, 70% of the irrigated area, 68% of food production, 81% of gross industrial output value, 87% of gross domestic product, and 75% of GDP in the province. Wei River is the only channel which can hold and discharge wasted and polluted water in Guanzhong area, though which more than 80% of industrial wastewater and domestic sewage are discharged. As the water pollution controlling facilities has seriously lagged behind, a large number of ineffectively treated industrial wastewater and urban sewage had directly discharged into rivers. The water quality of the lower reaches of Wei Main Stream after Baojixia reaches to Grade V even super-V, generally losing the function of being used.This paper takes Shaanxi section of Wei River as the object of research, study the variation of water quality degradation as well as calculate the reduced capacity of water environment through the water quality monitoring, analysis and evaluation, which will make improvement of water quality in Guanzhong area and provide scientific basis of optimized water resources management.On the basis of the investigation of the water environmental problems in Wei River, we divided it into several sections such as Baoji, Xingping, Xianyang, Xi'an, Lintong, Weinan, Huaxian and Huayin according to socio-economic situation and administrative divisions, to investigate water pollution sources and monitor water quality indexes (chemical oxygen demand, hexavalent chromium, total phosphorus, ammonia nitrogen, hardness, etc.) Through the study of organic and inorganic indexes of monitoring data under different conditions such as at the same time by different monitoring sections and at different times the same monitoring sections, using Fuzzy Evaluation method and Matter Element Analysis Method, we conclude that the pollution of water is serious in this research area, and the sections of which their grades are reaching to V account for 70% of the total sections. In the calculation process, the reason that may cause inconsistent between Fuzzy Evaluation Method and Matter Element Analysis Method is founded, providing a scientific basis for the coordinated use of both methods. According to the condition of one-dimensional steady-state mathematical model, four representative sections were selected to analyze the degradation indexes in the study area, calculating four water quality indexes of water degradation such as hexavalent chromium, permanganate index, total phosphorus and ammonia nitrogen, in the following sections after the sewage outfalls of South Guozhen, Caijiapo, Xingping and Xianyang II Bridge. According to the monitoring data in the sections of research area and referring to the runoff characteristics of the Weihe River, capacity of the water environment, the quantity of pollutant discharge and the reduced amount were calculated out, which can make a conclusion that there is not additional available water environmental capacity in most of the research area, and emissions are very large, providing reference for the further study of the region's waste water treatment system construction and environment protection plans.At last, according to the investigation and references of the study area we consider that there exists environmental problems such as large amount of sewage discharging, low level of wastewater treatment process in industries, runoff reducing and sediment increasing, and put forward measures such as speeding up construction of sewage treatment factories, carrying out cleaner production and promoting the utilization of urban sewage and etc.