Current Articles

2023, Volume 34,  Issue 2

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Key scientific issues of hydrological forecast in the headwater area of Yellow River
YONG Bin, ZHANG Jianyun, WANG Guoqing
2023, 34(2): 159-171. doi: 10.14042/j.cnki.32.1309.2023.02.001
The hydrological forecast for the headwater area of Yellow River is of vital importance to the flood water resources utilization through optimal operation of cascade reservoirs over the Upper Yellow River such as Longyangxia and Liujiaxia, even to the prevention of flood and drought disasters for the entire Yellow River basin. However, the hydrological forecast in the source region is one of difficult problems in the current operational forecast of flood and discharge of Yellow River, due to the critical deficiency of ground-based rainfall observations and the lack of special hydrological model for high and cold mountain areas. This paper first reviewed the domestic and international related studies and then demonstrated the current status and technical level of hydrological forecast in the headwater area of Yellow River from three aspects including precipitation observation and precipitation forecast over ungauged areas with high altitudes, construction of hydrological model in cold regions and integration of meteorological and hydrological coupling forecast system, and meteorological genesis and formation mechanism of plateau precipitation occurrence. Subsequently, several key scientific issues existed in current hydrological operation forecast are systematically analyzed. Finally, it is suggested that the future studies of hydrological forecast in the headwater area of Yellow River focus on several important directions, such as the new-generation multi-source precipitation information fusion and assimilation, the development of specific hydrologic model for high and cold regions, the seamless ensemble forecast technique based on the meteorological and hydrological coupling, the analysis of multiple weather systems triggering heavy precipitation and continuous overcast rain.
Key scientific and technological issues of joint prevention and control of river flood and urban waterlogging disaster chain in megacities
LIU Jiahong, MEI Chao, LIU Hongwei, FANG Xiaoyi, NI Guangheng, JIN Wenbo
2023, 34(2): 172-181. doi: 10.14042/j.cnki.32.1309.2023.02.002
In recent years, the risk of extreme super rainstorm in megacities coupled with big flood in rivers has been increasing, which caused heavy casualties and property losses. It is necessary to carry out joint prevention and control measurements to cope with river flood and urban waterlogging disaster chains. At present, it is an urgent need to integrate multidisciplinary theories and methods of meteorological science, hydrological science, information technology, disaster prevention and mitigation technology, to solve the key scientific and technological issues. The key scientific issue is the combination mechanism of river-urban flood and the risk transmission rule of disaster chain. Besides, there are four key technological issues : ① To integrate the river and urban meteorological-hydrological observation facilities into a collaborative one to monitor and forecast the flood risk. ② Intelligent early warning and directional message broadcasting technology for river flood and urban waterlogging disaster chain. ③ Coupled simulation of river-urban flood and demonstration of joint prevention and control scenarios. ④ Intelligent decision-making technology for river-urban joint flood control and emergency plan preparation. Based on the collaborative observation of meteorology and hydrology, social and economic multi-source information convergence analysis, and disaster deduction model, an emergency command and decision support system could be built for joint prevention and control of river-urban flood. The system highlights real-time, dynamic assessment, precision and intelligence to support the whole-process river-urban flood regulation. It could provide technical support for flood forecasting, early warning, scenario-demonstration and emergency plan preparation in megacities.
Evolution characteristics of the interannual and intra-annual precipitation in China from 1956 to 2016
DU Junkai, QIU Yaqin, LI Yunling, LU Qiong, HAO Chunfeng, LIU Haiying
2023, 34(2): 182-196. doi: 10.14042/j.cnki.32.1309.2023.02.003
To analyze the spatio-temporal distribution pattern of precipitation in China, the trend and mutation characteristics of the annual precipitation, as well as the temporal and spatial evolution of the intra-annual distribution, are summarized and analyzed using multiple methods based on the fused monthly precipitation monitoring data of the water conservancy department and the meteorological department of 4 177 stations from 1956 to 2016. These methods include the Mann-Kendall test, PETTITT test, and vector algorithm for intra-annual distribution, which explores the distribution pattern of several indices, including the precipitation-concentration degree, precipitation-concentration period, and the proportion indices of the maximum accumulated precipitation in four months to one year. The following conclusions are drawn : ① The temporal and spatial distribution of precipitation across China is not uniform. In general, the annual precipitation decreases, and the concentration of annual precipitation distribution increases from southeast to northwest; the changing trend of the annual precipitation at the stations shows a strong zonality with three bands of "increase-decrease-increase" from the southeast to the northwest; the bands showing a significant increase are located in the Southeast and Western China, and the bands showing a significant decrease are located in the central region, stretching from the northeast to the southwest to the border; and abrupt changes are often accompanied with the trend changes of the annual precipitation, of which most sites occur in the 1980s. ② Along the 200 and 400 mm annual precipitation contours, one band shows "flood season precipitation reduction" with strong temporal variation in North China. On the monthly scale, the proportion of precipitation in the flood season of the station decreases, and it increases in the non-flood season, while the opposite is true on the daily scale. The amplitude of accumulated precipitation for 3—7 consecutive days increases, suggesting that the extreme degree of precipitation events is increasing. ③ The changes in the precipitation series and the changes in the runoff series are well synchronized. The annual precipitation in Northwest and Southeast China shows an increasing trend, and the statistical discharge of the typical hydrological stations increases synchronously. However, the stations at which the annual precipitation decreases significantly and where the proportion indices of the maximum accumulated precipitation in four months to one year declines more than 10%, are concentrated in the non-humid areas of Northern China, such as the Liaohe River basin, Haihe River basin, and Yellow River basin. In these regions, the statistical discharge of the hydrological stations has decreased significantly.
Partition adaptive model of urban rainstorm and flood process based on the simulation concept of plots generalization and road networks fine
LI Donglai, HOU Jingming, SHEN Ruozhu, GAO Xujun, HUANG Miansong, MA Yue
2023, 34(2): 197-208. doi: 10.14042/j.cnki.32.1309.2023.02.004
To address common issues in urban catchment-scale rainfall-runoff simulations, such as inadequate topographic and drainage data, concentrated flooding on the road area, and the poor calculation accuracy or low calculation efficiency of the existing flooding models, a partition adaptive model based on the concept of plot generalization simulation and road networks fine simulation is proposed. For plots with insufficient data, sub-catchment units are divided, and the hydrological generalization method is used to calculate the runoff generation and concentration process. For the road area, fine grid division is carried out, and the two-dimensional hydrodynamic method is used to simulate the flow movement process. Both methods are coupled with the pipe network model to jointly drive the pipe network model to perform the confluence process calculation. The core demonstration area of Fengxi New Town in Xixian New Area is used as the research object to build a partition model. Besides, the full-distributed model with the study area discretized by fine grids and the semi-distributed model with the study area discretized by coarser sub-catchments are applied in the same area for comparison. The results show that : ① The partition model has the advantage of comprehensively considering the drainage of plot drainage and runoff process, and can simulate the inundation process in low-lying areas of road under the combined effect of surface runoff and pipe network overflow, which conforms to the actual rainfall flow motion. ② Compared with the semi-distributed model, the partition model can better simulate the process of water accumulation in the road area by using fine grids. ③ Since the calculation task of the partition model is less than that of the full distribution model, simulation time can be reduced by 28.2%—73.5% under different return periods. The new partition model effectively overcomes limitations of data conditions and computing power, and can provide a new coupling simulation idea for urban flood simulation.
Simulation of the flood process in urban surface-underground space under extreme rainfall
GUO Yuan, WANG Luyao, CHEN Nengzhi, JIN Juxiang
2023, 34(2): 209-217. doi: 10.14042/j.cnki.32.1309.2023.02.005
Urban waterlogging due to extreme precipitation presents an increasingly serious challenge. Pooling of large volumes of surface water can result in flooding of underground spaces. However, there remains limited studies on flooding of underground spaces through the application of hydrological and hydrodynamic models. This study examined flooding in an urban district of Zhengzhou City, China during an extreme rainstorm event on 20th July, 2021. An integrated simulation model of regional surface and underground spaces was established based on InfoWorks Integrated Catchment Model (ICM) software. The generalized reservoir and hydraulic connectivity methods were used to simulate underground spaces. Factors contributing to the initiation and development of flooding of underground spaces were analyzed. The results showed that underground waterlogging was less conducive to alleviation of surface water ponding. The advantages of the generalized reservoir method were shown to be its relative simplicity and feasibility, whereas that of the hydraulic connection method was its detailed representation of underground flooding. Both the cumulative quantity of rainfall and rainfall intensity were shown to have important effects on underground inundation. The results of this study can help to improve urban stormwater forecasting and warning systems, and provide a theoretical basis for regional disaster prevention and reduction.
A coupling 1D-2D model of urban flooding simulation based on improved vertical flow exchange method
JIN Xi, ZHOU Pengfei, ZHANG Xiangling, LIU Chengyu
2023, 34(2): 218-226. doi: 10.14042/j.cnki.32.1309.2023.02.006
Aiming at the complex calculation process and poor stability of vertical flow exchange in one-dimensional and two-dimensional coupled model for urban flood, an improved vertical flow exchange method is proposed based on the principle of node water balance. The nodes of one-dimensional model are divided into overloaded nodes and non-overloaded nodes. For overloaded nodes, the principle of node water balance is used to calculate the vertical exchange flow, and the vertical exchange flow calculation is integrated with the hydraulic calculation of one-dimensional model to realize simultaneously solving of node vertical exchange flow and pipe flow. For non-overloaded nodes, the variable head orifice outflow formula is used to calculate the vertical exchange flow, so that calculation of node backflow considering change of surface water depth is realized. Using the Infoworks ICM model as a comparison, simulation results of different cases are compared. Compare results show that the proposed method has a high degree of agreement with the simulation results of contrast model (Nash-Sutcliffe efficiency coefficients are larger than 0.8), and the proposed method has the ability to simulate vertical flow exchange process accurately and ensures water balance of the system. Therefore, the coupled model with improved vertical flow exchange method has significant application value for urban flood simulation.
Evaluation of the suitability of groundwater recharge in typical areas of the Haihe River basin
CAO Wengeng, WEN Aixin, NAN Tian, WANG Zhe, GAO Yuanyuan, CUI Yali, SUN Xiaoyue
2023, 34(2): 227-237. doi: 10.14042/j.cnki.32.1309.2023.02.007
The Daqinghe River basin is the most prominent area of groundwater overdraft in the Haihe River basin.In order to solve the problem of groundwater overdraft, this study carried out the suitability evaluation of integrated groundwater recharge in mountainous and plain areas in the basin.Select the buried depth of groundwater level, permeability coefficient, distance from the main canal of the middle line of the South-to-North Water Transfer, distance from the reservoir, precipitation infiltration coefficient, effective water storage space, slope, and surface elevation to build the GIS-AHP decision model to obtain the zoning map of the suitability of the study area, and use numerical simulation to evaluate the effect of the replenishment.The study shows that the suitable areas for recharge are mainly distributed in the piedmont reaches of Juma River, Qinglong River, Tanghe River and Cihe River, accounting for 4.5% of the total assessed area; at the same time, according to the assessment results of the suitability of recharge, the refined water replenishment scheme for river sections can greatly slow down the decline rate of groundwater storage variables, and the recharge is the best.Therefore, the suitable assessment of groundwater recharge in the basin based on the combination of GIS and numerical simulation is helpful to greatly improve the utilization efficiency of water resources in the region and provide the optimal over-extraction control scheme.
Study and application of a coupled modelling of flow-sediment transport and hydropower generation in the Sanmenxia Reservoir
XIA Junqiang, ZHANG Xianziyi, WANG Zenghui, ZHOU Meirong, LOU Shujian
2023, 34(2): 238-249. doi: 10.14042/j.cnki.32.1309.2023.02.008
To obtain a compromise between the short-term benefits of water resources utilization and the long-term benefits of sedimentation reduction in reservoirs constructed in a heavy sediment-laden river, it is of great significance to study the comprehensive benefits of sedimentation reduction and power generation by means of mathematical modelling.Fully incorporating the interaction between flow and sediment transport and bed deformation processes, a numerical model coupling flow-sediment transport and power generation is developed by integrating a 1-D morphodynamic module, a reservoir operation module and a power generation module.The proposed model was respectively calibrated and verified with the measured hydrological and electric data in the Sanmenxia Reservoir in 2019 and 2020, and moreover the influences of different hydrological regimes and operation schemes on sedimentation volume and power generation were analyzed.The results show that the calculated values of water level, discharge and sediment concentration were in good agreement with the measured values, and the relative error of power output was within 15%, so the model can be used to simulate the processes of both bed deformation and power generation in reservoirs reasonably well.The variations in the amounts of sedimentation volume and power generation can reach 129%—360% and 18%—52% respectively, compared with those under the condition of large water volumes and small sediment discharges.Lowering the initial pool level of the non-flood season can control the sedimentation in a non-flood season, and increasing the critical inflow discharge for sluicing in a flood season can improve the comprehensive benefits of sedimentation reduction and power generation.
Linkage relationship of beach/central bar and waterway shoal obstruction mechanism in Luochengzhou reach of the lower reaches of Yangtze River
YANG Yunping, ZHANG Xiabo, ZHENG Jinhai, ZHU Lingling, WANG Jianjun, FANG Juanjuan, WEI Wen
2023, 34(2): 250-264. doi: 10.14042/j.cnki.32.1309.2023.02.009
There is a strong correlation between waterway shoal evolution and boundary shoal morphology adjustment.Combining with effects of unbalanced channel scouring and distribution, scouring and sediment supply of upper reaches, these make waterway shoal obstruction mechanism more complicated.In this study, the Luochengzhou reach in the tidal reach of Yangtze River is taken as the object.By analyzing the morphology of the shoal, the characteristics of riverbed scouring and deposition, the hydrodynamic environment and the navigation-obstructing characteristics of the central bar and beach during 1959—2021, we clarified the linkage relationship between the evolution of the central bar and beach the waterway shoal, and the scouring and sediment supply of the upstream riverbed and its influence mechanism on the evolution of the waterway shoal.Since 1981, the Yangzhong reach where the Luochengzhou reach is located has changed from siltation to continuous scouring since 1991.The scouring amount of the low-water channel from 1981 to 2021 is 3.97×108 m3, accounting for 95.9% of the flood channel scouring volume; before the operation of the Three Gorges Project, the collapse of Sima bend area, the siltation of the left margin of Luochengzhou, and the undeveloped of the Sanyiqiao beach are the chief reasons for the collapse of Sima bend area.After the operation of the Three Gorges Project and before the implementation of the waterway regulation works, the decrease of sediment inflow caused the overall erosion of the shore, and the scouring of Luochengzhou provided the development space for the Sanyiqiao beach, the gradually silted Sanyiqiao beach and the runoff and sediment conditions jointly led to the development of the scouring of Luochengzhou and the right branch, that is, the change of the shape of the Sanyiqiao beach gradually changed from passive siltation to the main cause of the intertidal evolution.During 1981—2010, the sedimentation of Sanyiqiao beach, the erosion of the head and left edge of the Luochengzhou reach determined the degree of navigation obstruction of Sanyiqiao beach.Due to the riverbed scouring caused by the reduction of sediment inflow in the basin, the degree of navigation obstruction is weakened.From 2011 to 2021, the left edge boundary of the Luochengzhou is gradually stabilized and the waterway conditions in the lower shallow area are improved.At the same time, the area of the Sanyiqiao beach is changed from siltation to small scouring, and the navigation obstruction position is gradually raised to form the upper shallow area.Since the implementation of the second phase of the project, the changes in the basin inflow process conditions, Sanyiqiao beach scouring and the relative development of the right branch of Luochengzhou are still not conducive to the stability of the waterway conditions of the foreshore section of the Luochengzhou reach.It is suggested that engineering measures to stabilize the boundary of the shoal and limit the scouring development of the right branch should be taken in the subsequent improvement of the project.
Evolution of braided channels at the confluence of Yarlung Tsangpo and Niyang River from 1986—2021
YOU Yuchi, LI Zhiwei, YU Guo′an, HU Xuyue
2023, 34(2): 265-276. doi: 10.14042/j.cnki.32.1309.2023.02.010
The morphology and variation of braided channel at the confluence reach of Yarlung Tsangpo River (YTR) and Niyang River are affected by the inflow of Niyang River, valley boundary and vegetation conditions.The spatio-temporal variation and complexity of of the braided river are of importance to further study.The remote sensing images from 1986 to 2021 were used to extract the morphological features of braided channels, sandbar and vegetation (channel migration rate, sinuosity, area, et al).We further analyze the morphological characteristics and evolution processes of complex braided channels.The results show that maximum migration rate of the main channel is 483 m/a, the sinuosity reduces by 3.43%, and the vegetation cover area increases up to 8.05 km2.Owing to the difference of boundary conditions and hydrological conditions, the main channel of the Milin-Paizhen reach oscillates laterally before the Niyang River flows into the YRT, and migrates laterally and longitudinally after Niyang River flows into the channel.Since 2013, 11.8% of the vegetation coverage in the river channel has a positive feedback of erosion inhibition and deposition promotion, and enhanced the stability of the sandbars.
Factors controlling sediment yield and prediction of ungauged areas in the Lower Jinsha River basin
TAN Yuning, LIU Huaixiang, LU Yongjun
2023, 34(2): 277-289. doi: 10.14042/j.cnki.32.1309.2023.02.011
Recent installment of cascade reservoirs in the Lower Jinsha River basin urges quantitative studies of sediment inflows from ungauged tributaries and sediment pattern in this basin.Based on existing observations from 18 gauging stations and a multi-factor dataset, the Spearman rank correlation analysis was used to examine the responses of sediment yield to potential controlling factors at the catchment scale.Dimensionality reduction and regression methods were integrated to identify different sets of factor variables for predicting specific sediment yield (SSY).The results show that proportion of slopes over 8°, temperature and catchment area together can best describe the regional mechanism of sediment yield, and the obtained model explained 92% of SSY variability.The estimated SSY of ungauged areas varied from 87 t/(km2·a) to 1 189 t/(km2·a) and has reduced by 50—300 t/(km2·a) over the past 50 years.This research detected both high-yield and low-yield tributaries in the Baihetan and Xiluodu reservoirs, as well as the declining trend of SSY spatial heterogeneity.
The influence of seepage on bank collapse of muddy tidal channel: three-dimensional physical model
GONG Zheng, TANG Shuai, ZHAO Kun, ZHANG Kaili
2023, 34(2): 290-298. doi: 10.14042/j.cnki.32.1309.2023.02.012
Tidal channels migrate frequently under the combined actions of coastal dynamics and bank collapse, significantly affecting the stability of tidal network systems. However, existing studies mainly focus on in-channel flow erosion during flood tides, while less efforts are devoted to bank retreat driven by seepage erosion during the ebb tides. It is thus urgent to understand the underlying mechanism of bank collapse that driven by seepage. This study investigates the impact of seepage head height on bank collapse through physical experiments, including bank collapse modes, bank line variations and bank retreat rate. Results show that the process of bank collapse is related to seepage head height. We observe a transition of bank collapse mode from cantilever failure to tension failure, with increased seepage head height. A positive correlation between bank retreat rate and seepage head height is found. Overall, this research reveals the mechanism of bank collapse driven by seepage, and explains the distinct failure process of bank collapse over ebb tides, which is of great significance to the study of tidal channel evolution.
Experimental study on turbulence characteristics of open channel flow beneath an ice cover
CHEN Gang, DONG Zengchuan, WANG Haijun, GU Shixiang, YANG Hongxuan
2023, 34(2): 299-309. doi: 10.14042/j.cnki.32.1309.2023.02.013
River ice, as a vital component of the terrestrial cryosphere, alters the structure of under-ice flows during its evolution.The hydraulic regimes of ice-affected streams may be classified as fully-open, completely-covered, and partially-covered.Using experimental measurements from an acoustic Doppler anemometer, the turbulence characteristics of steady uniform flow under three different hydraulic regimes were studied in terms of streamwise velocity, Reynolds stress, and turbulence intensity.The results showed that for the completely-covered case, the streamwise velocity profile exhibits an asymmetric -shape with the maximum value closer to the smooth boundary, the Reynolds stress profile is linearly distributed in the depth direction, and the turbulence intensity profile for two flow layers based on the two-layer hypothesis may be described by an index relationship.The flow structure in partially-covered channels shows a combination of hydraulic characteristics from fully-open and completely-covered flows.Owing to the effect of lateral momentum transfer, the vertical profiles of the Reynolds stress and the turbulence intensity in the under-ice, open-water, and transition subsections differ from each other.The experimental results can provide theoretical guidance for ice-related disaster prevention and water supply security.
Coastal dynamic geomorphology under high intensity disturbance: research progress and perspectives
WU Zhiyuan, JIANG Changbo, CHEN Jie, DENG Bin
2023, 34(2): 310-320. doi: 10.14042/j.cnki.32.1309.2023.02.014
The coastal zone is the strongest interaction zone among the land, ocean, and atmosphere, and it is also the area that is most affected by global climate, sea-level change, and human activities.The dynamic process of the coastal zone has obvious characteristics of the ocean-shelf-bay-coast multi-scale and multi-physical field, and its dynamic geomorphic process and response mechanism are special.The frequent occurrence of extreme meteorological events, such as typhoons, and the impact of strong human activities, such as engineering measures, have led to greater uncertainty in the dynamic geomorphic evolution of the coastal zone.The research progress of coastal dynamic geomorphology under high-intensity disturbance, extreme conditions, and strong human activities is summarized herein.Owing to the complexity of the multi-scale dynamic process of the coastal zone and the internal mechanism of coastal geomorphology response under the joint action of global climate change and human activities, it is necessary to study the characteristics of coastal dynamic geomorphology and explore the dynamic process and response mechanism of the coastal zone under high-intensity disturbance in the future from the multi-physical field perspective of atmosphere-wave-ocean-sediment, from the multi-scale perspective of ocean-shelf-bay-coast, and from the multi-process perspective of dynamic-sediment-geomorphology.
2023, 34(2): 321-321. doi: 10.14042/j.cnki.32.1309.2023.02.015