The Fourier analysis is employed to study the effect of non-constant terms on the convergence properties of SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm formulated on a staggered grid in two-dimension. The results indicate the non-constant items can broaden the convergence range of pressure relaxation factor for a given velocity under-relaxation factor. What’s more, the non-constant items do well to the damping of the lowest error and can accelerate the convergence rate.
Songzikou has the greatest diversion ratio among the three outlets at Jingjiang River. The water and sediment diversion ratios are changed after water storage of the Three Gorges Reservoir. The changing trends are critical for the evolution of the river-lake relationship. According to the water and sediment diversion data obtained from 2003 to 2010 in the Songzikou, it could be found that the water diversion ratios in the Songzikou under different Zhicheng flow are enhanced and its sediment diversion ratios also had an increasing trend after the Three Gorges Reservoir storage. The variations were mainly related to the water levels of main streams, the change of river regime and the diversion angle near the outlet. In addition, the changes were also associated with the evolution characteristics of outlet channel. We further studied how flood regulation of the Three Gorges Reservoir influenced the diversions of the Songzikou.
In this study, an empirical curve describing the relation between erosion and deposition rate and water/sediment discharge was developed based on the recent evolution trend of the submerged delta at the Yangtze River Mouth, and the one-dimensional mathematical model for unsteady water-and sediment-transport was calibrated using the water and sediment discharge data after water impounding to predict the water and sediment discharge for the future 10 years and the future evolution of the submerged delta at the Yangtze River Mouth. The results showed that the 10 m and 20 m isobaths areas of the submerged delta changed with the water and sediment discharge from siltation to siltation slowing down to erosion. Siltation increased with large amount of rain received by the watershed during 1997-2000, while continuous retreat of erosion happened during 2000-2009. Using the one-dimensional mathematical model for river water and sediment calibrated and tested with data collected after impounding, the water and sediment discharges were calculated for Series 60 and 90, and its evolution in 2013-2022 was predicted for the delta. For Series 60, its 10 cm and 20 cm isobaths areas showed alternative scour and siltation, while the delta showed trends of erosion. For Series 90, its 10 m and 20 m isobaths showed substantial siltation in flood years. The water and sediment discharges since the Three Gorges Reservoirs was filled were lower than the calculated results for both Series 60 and 90. If the water and sediment discharges continue to decease, the delta will take an erosion trend.
SonTek’s Riversurveyor Catamaran (the RiverCAT) is a fully integrated river discharge measurement system. In this paper, the RiverCAT is applied to measure the topography under water in a middle industry water supply reservoir. The whole measurement process is introduced. Area of each cross-section is calculated with complex trapezoidal quadratic formula, and the capacity of the reservoir is computed with complex prismaid quadratic formula. The relationship between capacity and water level is researched by regression analysis method.
The deposition rate of the delta decreased when seawards sediment decreased. The critical values of sediment concentration mean the concentration which kept balance of erosion and deposition. According to the topography data of Yangtze estuary between 1958 and 2007, the change process of the isobaths is established. Based on the datum line of east longitude 122°17′, the empirical relation between the erosion/deposition rate of delta and the sediment amount was built and the critical values were calculated. The trend of the change of sediment concentration was also forecasted. The isobaths of -10 m, -15 m and -20 m have been eroded from 2000 to 2007 because of the decrease of the sediment discharge into the sea. The critical values of the isobaths of -10m, -15m, -20m is 24.88, 24.23, 20.40 million tons per year and the numbers are decreasing in the deep sea.
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