The Pollution Content Research Of Yangtze River In Three Gorges Area Using QUAL2E Model

This study of the Yangtze River water quality in Chongqing municipality's part of the Three Gorges reservoir area contributes to a better comprehension of the impacts of the Three Gorges Project on the river water quality. The aim of this research is to explore the combine effects of the socio-economic development of the area, the influence of the Yangtze River background pollution, and the construction of the Three Gorges dam. This research uses the U.S. EPA QUAL2E model to simulate the river water quality in the reservoir area. For the purpose two pollutants, the chemical oxygen demand (COD) and ammonia (NH3-N) have been used to simulate the water quality by the target year of 2006. These two pollutants have been chosen because of their data availability for all the river sections. This research concerns only the impoundment level of 135 m. The study area covers 364 km, from Fuling to Wu Shan and has been divided into six reaches. First, the socio-economic information about the study area have been given, data about the hydrologic conditions of the Yangtze River before the reservoir impoundment both at dry and wet seasons have been gathered, and the pollutants load forecasted for the target year of 2006. Then the QUAL2E model has been used to simulate the river water quality.By the year 2006 the hydrologic conditions of the reservoir area will be similar to the actual conditions and the water level will still be at 135 m. After analyzing the hydrologic conditions we found that the impoundment of the Three Gorges reservoir has changed all the characteristics of the Yangtze in the reservoir area, in fact, the river has been changed into a reservoir that means, increase of the river width, the river depth and consequently the river cross section area. Before the impoundment, the cross sections in dry and wet seasons were respectively 5684 m2 and 12400 m2 in Fuling reach; 2980 m2 and 11300 m2 in Fengjie reach, they are now 12240 m2 at Fuling and 44608 m2 at Fengjie. These changes of the cross section will slowdown the flow velocity that will also decrease the self-purification ability of the river. Before the impoundment, the mean flow velocity was about 1.91 m/s in wet seasons, and 0.73 m/s in dry seasons at Fuling; 1.97 m/s in wet seasons and 0.93 m/s in dry seasons at Wanzhou; 2.18 m/s in wet seasons and 1.56 m/s in dry seasons at fengjie. After the impoundment (water level 135 m), the flow velocity is 1.26 m/s at Fuling, 0.43 m/s at wanzhou, and 0.32 m/s at fengjie.The Two pollutants loads have been forecasted for the year of 2006 on the basis of 1998 and 2001 loads. The forecast shows that in all the sections and for all the two pollutants, the predicted pollutants loads show moderate values due to the construction of wastewater treatment plants in all the cities along the Yangtze in the reservoir area. In all the sections and for all the pollutants there has been and increase in the loads compared to the loads in 2001 except the Wanzhou District where the NH3N load will decrease.QUAL2E has been applied to a 364 stretch of the Yangtze River to determine COD and NH3-N concentrations as arbitrary non-conservative constituents. The model has been run for a steady state simulation where no climatological data is needed. For this simulation we haven't do a strong calibration and most of the parameter are used as QUAL2E default values. The five main tributaries of the Yangtze in the area are not taken in the simulation. The simulation output gives tendencies for both the hydrologic characteristics and the water quality variables. The COD output range from 14.81 mg/L in the headwater reach in Fuling section to 16.38 mg/L in the last element of the system in Fengjie reach. For NH3-N, the output ranges from 0.33 mg/L in the headwater element at Fuling to 0.76 mg/L in the most downstream element in Fengjie reach. These results put the Yangtze River in Class for the Fuling reach and Class III for the other reaches for COD and Class II for the Fuling, Fengdu and Zhongxian reaches, and Class III for Wanzhou, Yuny...