Preliminary Study On Roughness Variation During The Early Operation Period Of The Three Gorges Reservoir

The construction of the three gorges reservoir plays an important role to the sustainable development of social economy for our country, while the sediment deposition is one of the key technological problems. Due to the sediment deposition of three gorges reservoir will cause upstream backwater, and water level will be raised, the upstream backwater zone will be submerged and people’s safety will be affected. River roughness is key parameters of backwater calculation and sedimentation development after the reservoir operation, it has a direct impact on water level determine, flood safety, elevation of levee and factories design, calculation of reservoir flood capacity, accounting of irrigation capacity. Therefore, study on reservoir sedimentation in the process of the roughness change is great significance.Duo to the high cost of physical model and wide range of upstream backwater, mathematical model of one-dimensional flow will be combined with the theoretical analysis to study the roughness change on early operation period of the three gorges reservoir in this study.Through the analysis of sediment process, sediment deposition and water level changes in decade years for the three gorges reservoir operation, during the experimental impoundment period(2008 to 2012) of three gorges reservoir for 175 m level, the incoming runoff and long-time average annual value were almost the same, there was few changes on annual suspended load sediment discharge in drought season, and fewer signs was found in flood season, but the bedload sediment quantity is on the decline as a whole, the deposition which in discontinuous banded pattern mainly presented in wide valley but hardly any in valley, deposition mainly in perennial backwater zone from Fuling to downstream.To calculate the water level and the roughness caracteristic during experimental impoundment period(2008 to 2012) under normal water running stage of the three gorges reservoir, based on mathematical model of one-dimensional and measured data. Result indicate that, the calculated water line was highly consistent with the measured values, there has a good correlativity between roughness and the location along reservoir, the roughness along reservoir are changes in time and space.Analyze the calculation results under condition that water level in front of dam Z0=145m, flow capacity were 10000m3/s、15000 m3/s、25000 m3/s、34000 m3/s respectively, the roughness trend along with the change of time and space will be found for the streamwise straight area of perennial backwater zone, wide curving valley, wide branching valley, and typical alluvial river of fluctuant backwater zone.Comparison on the calculated roughness based on measured date and the result calculated by Hanqiwei interpolation formula for the streamwise straight area of perennial backwater zone and wide branching valley, the result and trend were similar for wide branching valley, and shows convex curves, then the Hanqiwei interpolation formula can be properly amended; Oppositely, the result and trend shows great difference for wide streight valley, it is required to fitting out the roughness interpolation formula for wide streight valley in perennial backwater zone.