Study On The Fluvial, Hydrodynamic And Water Quality Processes In Downstream Of Xiangjiang River

In this paper, by researching the hydrology data in resent years of section of Xiangjiang downstream, it is obtained that the regularities of the fluval processes of this section. By building the one demonsion hydrodynamic and advection-dispersion model of the section Xiangjiang River, we have the result that is including the characters of the hydrodymic and the veriation of the pollutants. On the basis, the focus of the research is on fluval process of the section which is effected by gravel mining, and the aspects as following:(1) The regulation of hydro project on the upstream lead to extend the diachonic of middle and small water in the section, increase the period of erosion, deduce the incoming sendiment, and necessarily inflict the channal erosion constantly growing; change of most of sand bars in the section is erosion in head, deposition in tail, and extending to downstream; the sand bars, extending to upstream, is effected by another sand bar which is near and at the upstream, or by the cutoff works of water at the bending parts; in the riverbed erosion processes, elevation contours of the sand bars, which is effected by the revetment buildings, is gradually cut and close up with the revetment building lines, and this should harm the security and stability of the buildings; effected by the gravel mining of human in the section, the hydrodynamic situation of the water worsen, and this is the main reason of fluval processes in the section; the movement of water level following with the change of discharge is augment.(2) Adopting the method of assign different roughness in different sections, and the calculated water level and the discharge is anastomosed with the measured ones, when the range of the roughness is in 0.027-0.033. However the roughness in this range, there are still errors between the calculated numbers and the measured ones, and the error distributing has the characters as following: the error is lower in high level than in the low level. According the actual situation of the Xiangjiang channal, the range of roughness, which is in 0.027-0.033, is reasonable. The primary reason of error is that: the talweg of the riverbed in this section is dishevelled, this cause the current scatter in low level period; and the river bed changed irregularly, lead to the veracity of terrain data in the model reduced, consequently, the final calculated numbers have the bigger discrepancy, comparaing with the actual numbers in low level period. (3) Drawing up 10 kinds different situation, which is composed of different discharge and water level, the simulation model calculated the water surface curve in different boundry condition, and the hydrodynamic simulation is the basis of the advection-dispersion.(4) Water quality model results are basically consistent with the trend of pollutant's movement, but because only the impact of upstream sewage is considered in the model, the sewage along the river is not quantified and taken advantage of, so the water quality simulation results can not fully reflect the actual changes of the water quality. Another factor which causes the deviation between numerical results and the actual monitoring results is the the existence of the conversion relationship among the five pollutants,this relationship is difficult to quantify.(5) Using ten different kind of hydrodynamic flow conditions, which is composed of different water levels and different discharges, analysis the pollutants effected by the hydrodynamic conditions. The effection is that, when the flow velocity is bigger (in the condition of the lower water level or the bigger discharge), the dispersion velocity of pollutants is faster, and the change of concentration is smaller, and the pollution last longer.