• 全国中文核心期刊
  • 中国科技核心期刊
  • 美国工程索引(EI)收录期刊

2020 Vol. 31, No. 4

Display Method:
On Three Gorges Reservoir control water level and operating conditions in flood season
WANG Jun, GUO Shenglian
2020, 31(4): 473-480. doi: 10.14042/j.cnki.32.1309.2020.04.001
Abstract:
As the cascade reservoirs in the upper reaches of the Yangtze River have been built and put into operation, the hydrological regime and functional requirements of the Three Gorges Reservoir (TGR) have changed significantly compared with that in the design phase. The reservoir operation of maintaining a fixed flood control limited water level (FCLWL) can no longer meet the needs of the new situation. In this paper, the feasibility of the dynamic control of the operating water level of the TGR during the flood season is demonstrated by analysing the setting conditions of the FCLWL during the design phase of the TGR, excavating the characteristics of the floods and the flood encounter rules in the basin. The results show that:① The applicable condition of the 145 m FCLWL in the design stage of TGR is to cope with major floods in the basin, and the occurrence probability of the basin-wide floods is small and has obvious characteristics, which can be predicted in advance by meteorological and hydrological forecast. ② According to the types of floods in the basin, division of flood stage and encounter rules of floods, when it is predicted that a regional flood will occur, FCLWL of the TGR will be set at 145 m from the beginning of June to the end of the Meiyu period, and then the water level will be gradually increased from the end of the Meiyu period to 155m by the 20th of August. ③ With the cooperation of meteorological and hydrological forecasting and joint operation of upstream reservoir group, the operating water level of the TGR during the flood season can fluctuate around 155 m in normal years, and earlier reservoir impoundment would be feasible. ④ The dynamic control of the water level of the TGR during the flood season will not increase the risk of flood control and siltation in the reservoir area. Or rather, it is beneficial to the hydrological regime and the relationship between the rivers and lakes in the middle and lower reaches of the Yangtze River, which can significantly improve the comprehensive utilization benefits of power generation, shipping, ecological protection and water supply.
Influence of the impoundment of cascade reservoirs on the asynchronies of flood peak and sediment peak in the Three Gorges Reservoir
ZHANG Wei, LI Xin, REN Jinqiu, DONG Bingjiang
2020, 31(4): 481-490. doi: 10.14042/j.cnki.32.1309.2020.04.002
Abstract:
After impoundment of the cascade reservoirs, the incoming suspended sediment in the Three Gorges Reservoir (TGR) greatly decreased, and the asynchronous characteristics of the sediment peak and flood peak in the TGR changed simultaneously. Therefore, it is necessary to study the asynchronous characteristics of the flood peak and sediment peak and their causes, which can provide a theoretical basis for understanding the mechanism of the asynchronous characteristics of the flood peak and sediment peak and for optimizing the regulation of reservoir sediment peak discharge. The observed data of the hydrological station in the TGR from 2003 to 2018 and a theoretical analysis were used to analyse the new asynchronous characteristics of the flood peak and sediment peak in the TGR after the impoundment of the Cascade Reservoirs and to preliminarily explore the factors affecting the asynchronous changes. It was found that after the impoundment of the Cascade Reservoirs, the asynchronism of the flood peak and sediment peak in the TGR was aggravated, which revealed that the proportion of the hysteretic sediment peak increased, the propagation time of the flood peak decreased, and the propagation time of the sediment peak increased. The reasons for these changes were the source of incoming sediment being switched to the TGR, the reduction in the flood peak and the increased particle size of the suspended sediment.
Morphological evolution and dynamic mechanics of the Jiuduansha Shoal (China) during 1959—2018
CHENG Haifeng, XIN Pei, LIU Jie, GU Fengfeng, WANG Wei, HAN Lu
2020, 31(4): 491-501. doi: 10.14042/j.cnki.32.1309.2020.04.003
Abstract:
This paper studies the morphological evolution and dynamic mechanics of the Jiuduansha Shoal (China), based on analysis of bathymetric data over the last 60 years (1959—2018). The results show that from 1959 to 1990, a natural evolution trend with relatively stable accretion rates occurred for the Jiuduansha Shoal particularly in the lower intertidal zone. During the last 30 years(1990—2018), the high mudflat of 0 m above the chart datum was subjected to rapid accretion due to the plant development and the construction of the Yangtze Estuary deep-water channel regulation project. During the last 20 years(1998—2018), the low mudflat 3 m below the chart datum was affected by the decrease in the river sediment supply and the adjacent large-scale water-related projects. The accretion rates slowed down and instead sediment erosion became to occur. During this period, the sediment reduction in the river basin led the slow-accretion mudflat to move upward in the Jiuduansha Shoal. In the future, the sediment supply in the river basin may keep decreasing and maintain a lower level. The low mudflat 3 m below the chart datum in the Jiuduansha Shoal will face a risk of further erosion, and the rest will be subjected to a decreasing accretion or sediment erosion.
Driving mechanism of Sanyiqiao point bar and shoal evolution in fluctuation segment of tidal current limit in lower reaches of Yangtze River
YANG Yunping, ZHENG Jinhai, ZHANG Mingjin, WANG Jianjun, ZHU Lingling
2020, 31(4): 502-513. doi: 10.14042/j.cnki.32.1309.2020.04.004
Abstract:
A strong correlation exists between the evolution of the point bar and shoal in the fluctuation segment of the tidal current limit in the lower reaches of the Yangtze River, with simultaneous influences from the hydrodynamic force of runoff and tidal currents, sediment sources, and human activities. This segment is crucial to channel regulation and dredging maintenance. Based on analyses of riverbed scouring and silting, branch channel diversion ratio, and evolution of Sanyiqiao point bar and shoal from 1976 to 2017, the driving mechanism of the evolution of this bar and shoal was clarified. Since 2012, at a depth of 12.5 m at the Sanyiqiao point bar, the shoal-body volume has been increasing. During high rainfall years, the point bar was dominated by silting, and the designed and deep channels were dominated by scouring. In medium rainfall years, the thickness of point bar deposition was less than that in the deep channel. Wufengshan bend in the upper reaches showed a stable river regime and had the functions of blocking the river regime of the upstream Hechangzhou River segment and adjusting the branch channel diversion ratio. The relationship between siltation at the Sanyiqiao point bar and the river-regime adjustment and branch channel diversion ratio of the upstream Hechangzhou River segment was not significant. It was mainly related to the scale and process of incoming flow in the river basin as well as scouring in the upstream river segment as sediment source. During the flood season, navigation obstruction in the upper shallow area of Sanyi Bridge was greater than that during the dry season. Navigation obstruction in years with a long duration of intermediate water flow before the flood season was greater than that during the same period in flood years (flow at Datong hydrological station was 26 000—34 000 m3/s). Therefore, the flow determined the scouring and silting distribution at the point bar and shoal, whereas the duration of intermediate water flow and amount of sediment supply determined the siltation volume at the point bar and shoal, respectively, obstructing navigation.
Dynamic geomorphological environment of large tidal channels in the South Yellow Sea and its response to human activities: a case study of Xiaomiaohong tidal channel
CHEN Kefeng, ZENG Chengjie, WANG Nairui, XU Junhui
2020, 31(4): 514-523. doi: 10.14042/j.cnki.32.1309.2020.04.005
Abstract:
Due to the lack of a fixed boundary, the stability of tidal channels in radial sand ridges is more sensitive to the impact of human activities. In this study, based on high-resolution underwater topography data of the Xiaomiaohong tidal channel in the southern part of the radial sand ridges collected over the past 20 years, the morphodynamic responses to the cumulative impact of human activities are investigated and simulated by numerical modeling. Results show that the section discharges at the tail, middle, and head parts of the Xiaomiaohong tidal channel induced by reclamation, which has reached 126.09 km2 in the past 20 years, are down 14.2%, 15.79%, and 9.13%, respectively; the average current velocities were also decreased by 20—30 cm/s, 10—20 cm/s, and 5—10 cm/s, respectively. The -5 m isobath on the southern side of the Xiaomiao channel has essentially remained stable with few changes; while the -10 m isobath is expanding westward and southward. Although the reclamation projects have resulted in a decrease of tidal capacity and hydrodynamics, the erosion and deposition they cause are restricted to the areas around the projects because of their high elevation. Overall, reclamation has little effect on the stability, southward moving, and the erosion trends of the Xiaomiaohong tidal channel.
Causes of local gravel deposition in gravel-sand transition of the Middle Yangtze River under clear water scour
XIONG Haibin, SUN Zhaohua, LI Ming, CHEN Li
2020, 31(4): 524-534. doi: 10.14042/j.cnki.32.1309.2020.04.006
Abstract:
After impoundment of the Three Gorges Reservoir (TGR), channel scour is ongoing in the reaches downstream the dam and gravel erosion, transport, and deposition have occurred in some areas of the gravel-sand transition (GST) of the Yangtze River. To investigate the causes of these phenomena, field data of flow, sediment and channel topography was collected and computational analysis was performed using a 2-D hydrodynamic numerical model. Especially, the spatial distribution characteristics of the incipient diameter under various discharges in the GST were simulated and examined. Impacts of the variations in river flow and the changes in water level downstream the reach on channel adjustment were also analyzed. The following results are obtained:① The large grain size gravel (D>30 mm) can be continuously transported along the entire GST when the incoming discharge is higher than 45 000 m3/s. On the contrary, the large grain size gravel is only locally transported in some shoal sections when the discharge lower than 15 000 m3/s. The flow dynamics are relatively weak for the transport of the same size gravel when the discharge ranges from 15 000 m3/s to 45 000 m3/s. ② The number of days with floods reduced and that with low discharge increased under the effects of the TGR operation. This trend is adverse to the long-distance transport of gravel. The water level lowering downstream the GST caused erosion in areas that previously remained stable. ③ The phenomenon of the local siltation was caused by the gravel transport in the GST driven by the increasing flow dynamics in the dry season. The main cause of this phenomenon is relevant to the special morphologic structures and sedimentary environment of the GST. This type of local bed adjustment may exist in the several locations within the GST for a long time and should receive considerable attention.
Formula of movable bed roughness for the Middle Yangtze River
LIU Xin, XIA Junqiang, ZHOU Meirong, DENG Shanshan
2020, 31(4): 535-546. doi: 10.14042/j.cnki.32.1309.2020.04.007
Abstract:
The computation of movable bed roughness is an important step in morphodynamic models. After the operation of the Three Gorges Project (TGP), a dramatic decrease of sediment load entering the Middle Yangtze River (MYR) caused the processes of channel degradation and coarsening of bed material, and the variation characteristics of the movable bed roughness became more complicated. Therefore, it is necessary to propose the formula of movable bed roughness for the MYR. Based on the 1 266 runs of measurements at five hydrometric stations such as Zhicheng, Shashi, and Hankou during the period 2001—2012, Froude number (Fr) and relative water depth (h/D50) were selected as the main factors influencing the magnitude of movable bed roughness. Based on the theory of flow regime partition, the formula of movable bed roughness was established and calibrated by these measurements using the method of multiple nonlinear regression. Finally, the predictive accuracy of the proposed formula was verified against 651 runs of independent measurements at those stations from the MYR during the period 2013—2017. The results indicate that:① the alluvial resistances in the MYR are in the lower or transitional flow regime for most of the time; and ② the calculation accuracy of the proposed formula based on the flow regime partition is significantly higher than the existing formulas with the determination coefficient (R2) of 0.89. Moreover, the Manning's roughness coefficients predicted by the new formula have the errors less than ±30% for 97.7% of the measurements.
Hydraulic characteristics of partially-filled flow in circular pipe
DING Falong, MAO Zeyu
2020, 31(4): 547-555. doi: 10.14042/j.cnki.32.1309.2020.04.008
Abstract:
Partially-filled open flow in circular-shaped pipe behaves unique hydrodynamic characteristics due to the special cross-section geometry. To investigate the peculiar characteristics caused by two-sides double-curvatures, a three-dimensional numerical model, based upon RNG k-ε turbulence model and FAVOR (Fractional Area/Volume Obstacle Representation) is established, and further verified using physical experiment results. The presented numerical model is then applied to simulate partially-filled flows with different combinations of slopes and filling degrees, in order to explore the velocity distribution, wall shear stress and Reynolds shear stress. The results indicate that velocity-distribution profiles along the different vertical lines generally follow a parabolic function, and a regression expression is proposed. A unified formula for the wall shear stress along wetted perimeter with different filling degrees is presented. The results also show that the Reynolds shear stresses linearly distribute along vertical lines. The larger the filling degree and distance from mid-perpendicular are, the smaller variation gradient of the stresses is. When filling degree is greater than 0.5, due to the influences of the secondary flow, the negative Reynolds shear stress appear along the mid-perpendicular.
Theoretical and experimental study on resistance characteristics of shrub vegetation distribution area
LU Yan, WANG Weixu, LU Yongjun, SONG Yuntao, YAN Dongliang
2020, 31(4): 556-564. doi: 10.14042/j.cnki.32.1309.2020.04.009
Abstract:
The water blocking law of the shrub vegetation distribution area in a river was ascertained by examining the characteristics and quantitative characteristics of flow resistance generated by shrub vegetation trunks and branches. Here, we present a prototype vegetation volume correction coefficient and a method for determining shrub vegetation hydraulic radius. The calculation formula of the shrub vegetation resistance coefficient is theoretically derived, and the relationship between the vegetation resistance coefficient and the vegetation Reynolds number with the characteristic length of the vegetation hydraulic radius is established in combination with a flume experiment. Our results indicate that:introduction of a prototype vegetation volume correction coefficient and a shrub vegetation hydraulic radius results in a more accurate shrub vegetation resistance calculation. The relationship between vegetation resistance coefficient and vegetation Reynolds number is an exponential function, and it decreases monotonically with an increase in the vegetation Reynolds number. Results from our flume experiment are in strong agreement with these findings.
Experimental study on typical parameters of thin layer flow of urban underlying surface under different rainfall conditions
LIU Fei, DONG Zhandi
2020, 31(4): 565-574. doi: 10.14042/j.cnki.32.1309.2020.04.010
Abstract:
Based on the rainfall intensity of the future science and technology city in Changping, Beijing, the experiments were taken through the indoor rainfall test platform. The changes of roughness coefficient, resistance coefficient and runoff coefficient of four typical impervious underlying surface (asphalt, concrete surface, SBS and concrete square brick) and four typical permeable underlying surface (lawn brick A, lawn brick B, aeolian sand brick A and aeolian sand brick B) were studied under eight kinds of constant rain intensity. The results show that the plane size, surface smoothness and material have obvious influence on the roughness and resistance coefficient of impervious underlying surface, while structure and material have obvious influence on the roughness and resistance coefficient of permeable underlying surface. The roughness value and resistance coefficient of these two types of underlying surface decrease with the increase of rain intensity. But the variation range is small, and then tends to be stable gradually. The runoff coefficient of these two types of underlying surface keeps relatively stable under different rainfall intensity.
Simulation and forecast of winter runoff in medium basin of Northeast China under climate change
WANG Zilong, HE Xin, JIANG Qiuxiang, LIU Ying, SUN Jian
2020, 31(4): 575-582. doi: 10.14042/j.cnki.32.1309.2020.04.011
Abstract:
To forecast winter runoff under future climate change, the Cold Region Hydrological Model (CRHM) platform was applied to simulate the winter runoff volumes during 2000—2012 and forecast the winter runoff volumes during 2025—2060 of upper reach of Yijimi River, a secondary tributary of China's Songhua River. The results indicate the following. ① Based on the changes of annual winter runoff depth and runoff coefficient during 2025—2060, the instability of winter runoff series would increase with increasing representative emission concentration. ② On the basis of location identification of mutation points, the higher the representative emission concentration, the greater the inflection point of accumulated winter runoff. ③ According to the correlation analysis, the climate in the same period is the main factor affecting monthly runoff in winter, and winter precipitation is the main factor affecting the changes of winter monthly runoff. ④ By comparison of cumulant slope changes, compared with the period 2025—2042, the contribution rates of winter precipitation growth to winter runoff growth during 2043—2056 and 2057—2060 are 39.8% and 62.6%, respectively. Compared with the period 2043—2056, the contribution rate of winter precipitation reduction during 2057—2060 to winter runoff reduction is 27.0%.
Analysis of urban design storm based on stochastic storm transposition
ZHOU Zhengzheng, LIU Shuguang, Daniel B Wright
2020, 31(4): 583-591. doi: 10.14042/j.cnki.32.1309.2020.04.012
Abstract:
Urban flooding is becoming more severe due to increases in extreme rainfall amounts and impervious land cover. Design storms are critical for developing infrastructure and land use solutions to these flood challenges. In this study, we examine urban design storms using Stochastic Storm Transposition (SST). SST is a technique that uses probabilistic resampling from a "storm catalog" of observed rainfall events selected from a pre-defined regional "transposition domain". Resampled storms are then spatially transposed to estimate distributions of extreme rainfall intensity, duration, and frequency (IDF). This study presents an SST-based rainfall analysis for Shanghai, China. Results show that there is spatial heterogeneity in rainfall across study's transposition domain which must be accounted for during the transposition step of SST. SST can reproduce reasonable IDF estimates and provide design storms with realistic spatiotemporal rainfall structures. Large variations in spatio-temporal structure of these SST-based design storms under different return periods call into question the conventional hydrologic engineering assumption of design storm rainfall that is spatially-uniform and temporally idealized.
Experimental study on the influence of drift flow on the propagation characteristics of wind waves in shallow lakes
GAO Ang, WU Shiqiang, WU Xiufeng, WANG Fangfang, DAI Jiangyu, SONG Kai
2020, 31(4): 592-600. doi: 10.14042/j.cnki.32.1309.2020.04.013
Abstract:
Wind waves are mostly in the development stage in areas such as shallow lakes and other places with limited wind blowing range and water depth. The surface drift flow generated by wind may affect the propagation characteristics of the wind waves. Wave parameters, such as wave celerity and wavelength, are difficult to be obtained through the dispersion relations of the linear wave theory. To accurately forecast the parameters of the wind wave in shallow lakes, the influence of drift flow on wind wave propagation in a wind tunnel was investigated by considering the characteristics of shallow lake's limited blowing range and water depth. The results showed that the drift flow, stokes flow and surface flow were all positively correlated with the wind speeds. With the increase of wind speed, the ratio of the drift flow to the surface flow gradually decreased and stabilized at the value of 75%. The drift flow could promote the wave celerity and wavelength, especially for small-scale waves. Nonlinearity of waves suppressed the effect of drift flow on the wave celerity and wavelength. The empirical dispersion relation of wind waves and empirical relation of dominant frequency wave celerity, considering the influences of drift flow, are established.
Study on the mutual feedback relation among water supply-power generation- environment of reservoir group in the upper reaches of the Yangtze River based on gradient analysis method
HE Zhongzheng, ZHOU Jianzhong, JIA Benjun, ZHANG Yongchuan
2020, 31(4): 601-610. doi: 10.14042/j.cnki.32.1309.2020.04.014
Abstract:
The optimal regulation of the coupled system of water resources in the upper reaches of the Yangtze River involves the competing and incommensurable objectives of water supply, power generation and ecological water requirements. It is difficult to analyse and describe the mutual feedback covariance mechanism of the water supply, power generation and environment and to balance and optimize the regulation of multiple objective benefits. Based on the theory and method of multi-objective optimization and operational research, a method to study the mutual feed relationship among water supply, power generation and the environment is proposed using gradient analysis. The multi-objective constrained optimization method is used to obtain the Pareto optimal solution set of the joint optimal operation of the reservoir group in the upper reaches of the Yangtze River within the objective space of the water supply-power generation-environment, and the multi-objective space surface of the mutual feed relationship of the water supply-power generation-environment is constructed by interpolation. Thus, the first-order difference approximation is used to acquire the partial derivative function values of the water supply to the environment and power generation to quantify the gradient of the environmental response to changes in the water supply and power generation. Then, the mutual feed covariance relationship of the water supply-power generation-environment is analysed. This method provides a new approach for studying the multi-objective mutual feed relationship of the optimal operation of the reservoir group.
Effectiveness of urban inundation control system in sponge city construction
LIU Jiahong, WANG Jia, WANG Hao, MEI Chao
2020, 31(4): 611-618. doi: 10.14042/j.cnki.32.1309.2020.04.015
Abstract:
The urban inundation prevention effect of "sponge city" has not fully achieved the expected objectives. Basic research on the subject is relatively inadequate. To address this issue, this study examined the construction mode of urban inundation control systems in sponge cities, including the source control system (SCS), municipal drainage network system (DNS), and over standard stormwater storage and drainage system (OSS). The functions of the SCS, DNS, and OSS were quantified based on the local rain pattern in Tongzhou, Beijing. Under a 50-year rainfall event (339.85 mm/d), the design rainfalls of the SCS, DNS, and OSS were 34.00 mm, 130.70 mm, and 175.15 mm, respectively. Urban inundation control mechanisms were revealed by using a Gaussian function. The evaluation process of the urban inundation control function was transformed into a process of estimating the parameters of the Gaussian function. A method of optimizing the urban inundation control system is proposed for sponge city construction based on a cost-benefit analysis. The effectiveness of urban inundation control, the life cycle cost, and the covered area are adopted as decision indicators, while the maximization of cost-benefit per unit area under different scenarios is adopted as the objective function.
Review of sediment yield, transportation, and trap in reservoirs in Lancang-Mekong River basin
HOU Shiyu, TIAN Fuqiang, NI Guangheng
2020, 31(4): 619-628. doi: 10.14042/j.cnki.32.1309.2020.04.016
Abstract:
The Lancang-Mekong River is one of the largest transboundary river shared by China and Southeast Asian countries. In recent years, the sediment issue in this large river has received extensive attention due to nutrient-rich sediment decreasing which is critical to ecological health, aquatic habitats, shipping, coastal erosion and agricultural and fisheries production. A wide range of studies on sediment yield, transportation and trapped by reservoirs are summarized. The main controversial topics include where the most sediment comes from, how to explain the abnormal relationship among suspended sediment loads observed along the mainstream, and the quantification of effect of human activities on sediment load change. There are five main issues unsolved, including unreliable observed sediment data in Lower Mekong River, weak basis of total sediment load of 160×106 t/a, low spatiotemporal resolution in model simulation, insufficient study of the land use change impacts in recent decades and inadequate research on sediment except for suspended sediment. Several possible ways to overcome these difficulties are also discussed.