| After Three Gorges Reservoir stores water, hydrodynamic condition changed ultimately at the branch rivers of Three Gorges Reservoir Area, velocity becomes slowly, self-purification capacity comes down. According to monitoring data, Reservoir Area tributary quality comes down year by year. Jialing River is the maximal tributary of Reservoir Area. Its water quality status is related to the Chongqing urban directly, and even Three Gorges Reservoir Area water environment situation. Therefore, carrying out the study of eutrophication problem on reaches in Chongqing main urban of Jialing River, which is important significance to sustainable development and the organism's habits harmony of Chongqing urban society and economy.The study is basis with Lake Eutrophication model. Consider the velocity is a major factor of restricting eutrophication, and critical velocity exists, the velocity factor has been led into alga growth item in the model. Velocity factor expression invented, which holds the critical velocity and the velocity effect modulus, and two dimension ecological model of reaches at Chongqing main city of Jialing River has been built. Applying monitoring data during February 6 till October 14 in 2007, to calibrate and validate the model. It finally indicates, simulate value and measure value having fairly good fitting. It indicate the model is reasonableness, and can be used to analyse eutrophication space-time distributes of reaches at Chongqing main urban of Jialing River and forecasts the eutrophication change trend. By carrying out numerical simulation study, some main conclusions can reach as following:①By comparision of TN, TP, velocity, Chla space distribution under difference water level conditions, it shows Chla is high relatively at small velocity area. During low water period, where there is high Chla, as well as TN and TP; During normal water period, TN, TP is unlikely high, since discharge is increasing, though N and P increased, and high velocity also make Chla lower than during low water period.②By modeling 4 kinds of water level difference in case of impoundment to study the effect to algae growth. Under the situation that upper lower reaches water level differs by 3.6 meters(Scheme 1), the water surface likely to occur water bloom accounts for 0.43%, and when upper lower reaches water level differs by 2.6 meters(Scheme 2), 1.6 meters(Scheme 3), 0.6 meters(Scheme 4), the water surface likely to occur water bloom accounts for 6.13%, 9.99%, 11.27% respectively. A conclusion can make here: the smaller water level difference, the more slowly water velocity, and the larger area of water surface which is probaly to occur water bloom.③The model has been used to model the effect to algae growth by the changing of TN, TP, light radiation and temperature. It shows that increase of TN, TP, light radiation and temperature all can greatly improve growth of algae at the beginning, but then the growth fall down and become more slowly when they get a certain value(TN is 1.7mg/L , TP is 0.12mg/L, light radiation is 11520 kJ/m2/d, temperature is 16.72℃).④By adding some point source, the results indicate that at the place of point source, though there is high TN, TP (TN is 2.46mg/L and TP is 0.36mg/L), if other conditions is not suitable, for example, velocity, light radiation and temperature, algae growth is likely not greatly improve.
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