Study On Backwater Area By Theoretic Analysis And Numerical Simulation At Changzhou Reservoir In Guangxi Province

As far as the waterway regulation in reservoir area is concerned, integrative measures should be taken in mountain river under different backwater conditions, because of the complexity of navigation-blocking conditions and diversity of flow result from river gradual exploitation. It is very necessary to do research into the rule of backwater length fluctuating. The main work of this paper was to study the rule of backwater length fluctuating at Changzhou Reservoir, by using the methods of theoretic analysis and numerical simulation. On the basis of theoretic analysis on the rule of backwater length varying with discharge, 2-D hydrodynamic-commercial software named SMS was applied into numerical simulation of backwater length. As a result, the consequence of theoretic analysis was verified and the effect of bottom slope on backwater length was discussed. Furthermore, the effect of the criterion for the terminal of backwater on the backwater length and its varying rule was discussed as well. Finally, the backwater lengths at Changzhou Reservoir under different operational conditions were computed with hydrodynamic-numerical model. The main conclusions are as follows:(1) Theoretic analysis showed that, there is an extremum in the range of backwater length variation. This means the backwater length increases with the increasing of discharge firstly, and then decreases gradually with the increasing of discharge. This conclusion is different from the traditional understand about the rule of backwater length variance.(2) Mathematic-model validation illustrated that there exits an extremum of backwater length exactly in the condition of certain water level and bottom slope, which verified the validity of theoretic analysis.(3) Bottom slope and criterion for the terminal of backwater determination may have effect on backwater length. Backwater length will increase with the slower of bottom slope. Meanwhile, precision of criterion for the terminal of backwater will have influence not only on the value of backwater length, but also on its varying rule even. The higher precision is, the greater extremum of backwater length is. The extremum may not exit while the criterion for the terminal of backwater has lower precision.(4) the results of backwater calculation at Changzhou Reservoir demonstrated that, there exited an extremal value of backwater length while the water level was 18.6m and the criterion for the terminal of backwater was 0.1m. The phenomenon of extremum exiting will be unobvious if the criterion was 0.2m or 0.3m.(5) For the catholicity of the consequence about criterion for the terminal of backwater determination in analytic calculation of backwater length, it can be used as reference frame in mathematic model calculation.