水科学进展

Investigation on the evolution trends and influencing factors of groundwater resources in China

CHEN Fei, XU Xiangyu, YANG Yan, DING Yueyuan, LI Jianqiang, LI Yuanyuan

2020, 31(6): 811-819. doi: 10.14042/j.cnki.32.1309.2020.06.001

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Groundwater resources have experienced significant changes in China in the past few decades. It is of significance to fully understand of the evolution trends and influencing factors of groundwater resources for groundwater management. Based on the data from National Water Resources Survey and China Water Resources Bulletin, the evolution trends and affecting factors of groundwater resources over past 60 years were investigated intensively. The results show that the quantity of groundwater resources has not changed a lot at the national level, but changes do occur in different areas in China; for instance, the groundwater resources of Haihe River basin, Liaohe River basin and Yellow River basin have dramatically shrunk. The recharge of groundwater has been increasingly influenced by human activities and artificial recharge has formed an important source for groundwater. More and more groundwater is discharged through human extraction while the discharge to river and evaporation from phreatic water decline. Additionally, the discharge of groundwater has already exceeded the recharge in Haihe River basin, Songhuajiang River basin, Yellow River basin and Northwest River basin, causing the imbalance of groundwater budget and overexploitation within these areas. Changes in precipitation, land surface conditions, and human activities were found as the main affecting factors for the evolution trends of groundwater resources.

Experimental study on the influencing factors of infiltration characteristics of abandoned grassland on slope scale in the loess hilly and gully region

XIAO Jing, WANG Bing

2020, 31(6): 820-831. doi: 10.14042/j.cnki.32.1309.2020.06.002

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To explore the influence of various factors on the infiltration characteristics of abandoned grassland in the loess hilly and gully region of the Loess Plateau, a natural rainfall field observation method was used to study the influence of rainfall characteristics (rainfall, average rainfall intensity, rainfall duration and the maximum 30 min rainfall intensity (I₃₀)), antecedent soil water content, slope length (10 m, 20 m, 30 m, 40 m and 50 m), and vegetation coverage on soil infiltration characteristics. The grey correlation method was used to determine the dominant factors affecting the infiltration characteristics of the abandoned grassland. It was found that the infiltration amount increased significantly with increasing rainfall, rainfall duration and I₃₀ (R²>0.55, P < 0.01). The infiltration supplement coefficient decreased with increasing rainfall, I₃₀ and average rainfall intensity (R²>0.12, P < 0.05). The average infiltration rate increased with increasing rainfall intensity and I₃₀ (R²>0.53, P < 0.01). The infiltration amount and average infiltration rate decreased with the increase of antecedent soil water content, whereas the infiltration supplement coefficient increased with the increase of antecedent soil water content (R²>0.13, P < 0.05). The infiltration amount, infiltration supplement coefficient and average infiltration rate increased as the slope length increased (R²>0.56, P < 0.01). However, there was a critical slope length between 30 m and 40 m. Rainfall characteristics and slope length were the main factors affecting soil infiltration, and the effect of vegetation coverage on soil infiltration was not significant as the infiltration efficiency was high.

Study on migration of different types water during farmland-wasteland-lake system in Hetao Irrigation District

WANG Guoshuai, SHI Haibin, LI Xianyue, YAN Jianwen, GUO Jiawei, LI Zhengzhong

2020, 31(6): 832-842. doi: 10.14042/j.cnki.32.1309.2020.06.003

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In order to find out the migration and transformation regularity of different types of water in cultivated land-wasteland-lake system, water samples were collected from representative sampling points in the system during the typical period from 2018 to 2019. The δ¹⁸O variation characteristics of different types water in different periods were analyzed, and the contribution rate of different types of water transformation was calculated by two-terminal element mixed model and soil hydrodynamics theory. The results showed that during the irrigation period, 82% of the irrigation water was stored in 1m soil, 18% of the irrigation water recharged the groundwater of cultivated land through leakage. 76% of the irrigation water of canal system contributed to the groundwater of cultivated land through underground lateral runoff. The average contribution rate of irrigation water and rainfall to cultivated land groundwater was 94% and 6%, respectively. The average contribution rates of cultivated land groundwater and rainfall to wasteland groundwater was 71% and 29%, respectively. The average contribution rate of wasteland groundwater and rainfall to lake was 43% and 57%, respectively. The amount of water contributed by canal system irrigation water to cultivated land groundwater through underground lateral runoff was basically transferred to wasteland groundwater. The transfer and transformation of groundwater was triggered by canal system water lateral runoff. The 5^th day after irrigation, saturated-unsaturated lateral recharge existed in 0-40 cm soil layer at the junction of cultivated land and wasteland. The 15^th day and 30^th day after irrigation, groundwater of cultivated land and the junction of cultivated land and wasteland recharged soil water in 40-60 cm(root zone), 80 cm and 100 cm soil layer. The 30^th day after irrigation, the irrigation water in the cultivated land disappeared. In non-irrigation period, wasteland groundwater and lake were consumed much water. Therefore, lake should be recharged water. The calculation results were demonstrated with relevant research, which were reliable and can provide important reference for water resources analysis of cultivated land-wasteland-lake system.

Experimental study on the effect of clogging on the inlet discharge capacity

XIA Junqiang, CHEN Qian, DONG Bailiang, ZHANG Xiaolei

2020, 31(6): 843-851. doi: 10.14042/j.cnki.32.1309.2020.06.004

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Street inlet is one of the key facilities in urbran drainage systems. Once street inlets are clogged, the surface water cannot be discharged efficiently into the underground pipes, which is one of the main reasons for the occurrence of severe urban flooding. In order to quantitatively investigate the influence mechanism and degree of street inlet clogging on its discharge capacity, experiments were carried out in a specific laboratory flume based on the condition of large incoming water depths, considering different clogging degrees of grate and lateral side tube respectively. A total of 608 groups of steady flow experiments were conducted. Experimental results show that the clogging of both grate and side tube can significantly influence the comprehensive discharge capacity of a street inlet, with the clogging of side tube having a more pronounced effect. The discharge coefficients were determined for weir and nozzle flows using these experimental data. Based on the dimensional analysis and the regression method, the formula of inlet discharge capacity expressed by a power function of clogging degree was proposed, and the coefficients were calibrated by experimental results. These results show that the latter calibrations based on the power function expression are better than that for the weir or nozzle formulae. The relationships between clogging coefficient and clogging degree were proposed respectively for inlet and side tube clogging, based on the non-linear fitting method and mean assumption of the power exponent. The unified formula for discharge capacity of street inlet was finally established, which can not only account for the weir and nozzle flow patterns, but also can reflect the effect of different clogging degrees of grate and side tube, and the proposed formula is applicable to large incoming water depths

Analysis of rainfall characteristics based on multiple types of rain gauges

LIAO Aimin, LIU Jiufu, ZHANG Jianyun, WANG Niu, LIAO Minhan, JIANG Guangxu

2020, 31(6): 852-861. doi: 10.14042/j.cnki.32.1309.2020.06.005

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A thorough understanding of the characteristics of rainfall helps conduct research on runoff simulation, soil erosion, climate change and so forth. In this study, in order to enhance the understanding of rainfall characteristics, six co mmon types of rain gauges (SL3-1, JDZ05, RG-3, Pluvio2, Parsivel2 and JQH-1) were deployed with pairs in the same experimental field, and the rainfall over five months was observed. The results of an intercomparison demonstrated the following:①Under moderate and heavy rain conditions (daily rainfall ≥ 10 mm), the total rainfall measured by SL3-1 and JDZ05 were within the error limit of 4%;however, under light rain conditions (daily rainfall < 10 mm), the total rainfall measured by the tipping-bucket and by weighing types of rain gauges were 4% less than JQH-1;② The frequency of rainfall intensity of ≤ 0.1 mm/min was almost higher than 75% for SL3-1, RG-3, Pluvio2 and Parsivel2, and the proportion of rain was more than 50% when the rainfall intensity was ≤ 0.2 mm/min; ③ The initiation times of rainfall, determined by Pluvio2 and Parsivel2, were 0.5 h and 2 h earlier than SL3-1, respectively, while the termination times of rainfall were 0.5 and 2 h later than SL3-1, respectively. These findings will allow researchers to select appropriate rain gauges to determine rainfall characteristics of interest.

Adjustment patterns and causes of the morphology of sandy riverbed downstream of the Three Gorges Dam

ZHAO Weiyang, YANG Yunping, ZHANG Huaqing, ZHANG Mingjin, YUAN Jing, YANG Baocen

2020, 31(6): 862-874. doi: 10.14042/j.cnki.32.1309.2020.06.006

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The operation of the Three Gorges Reservoir has altered the water and sediment conditions downstream of the dam, resulting in adaptive adjustments in riverbed by scouring and silting, as well as shoal and beach morphology. In particular, the sandy riverbed in the near-dam segment demonstrates the most sensitive response. In this work, the first sandy river segment of the Yangtze River was studied, and water and sediment data from 1955 to 2018 as well as topographic data from 1975 to 2018 were used to quantitatively study the characteristics and causes of riverbed erosion and deposition as well as the shoal and beach morphology adjustment. The results demonstrated that the riverbed underwent cumulative erosion as the sediment inflow from the river basin decreased. The amount of erosion in the low-flow channel accounted for 93.07% of the total amount of erosion in the river channel, and the area of shoals. After the 175 m impoundment of the Three Gorges Project, the scouring intensity downstream of dam on the riverbed increased, the near-dam segment with the greatest scouring intensity moved down to the sandy river segment, and sand excavation accounted for 15.9% of the scouring amount of the beach-level channel. The law of scouring and silting gradually changed from "scouring on low beaches and silting on high beaches" to "scouring on low and high beaches" since the impoundment. At the same time, the channel showed thalweg downcutting, the fluviatile facies coefficient decreased. Before the implementation of the waterway project, the evolution of beach groups demonstrated strong correlation. The channel bar development and downward movement of the head of the Taipingkou waterway caused the area of the upper section of the Lalinzhou point bar to decrease and recede. The tail area of the Lalinzhou point bar increased and the siltation width increased correspondingly, causing the area of the Sanba beach to decrease, the right edge to be eroded and recede, and the position of the beach body gradually move left. After the implementation of the waterway project, the correlation of beach group evolution was gradually weakened and the correlation between the channel bar of the Taipingkou waterway and the upper section of the Lalinzhou point bar was weakened. Moreover, the lower section of the Lalinzhou point bar was widened due to the influence of the waterway project as well as dredging and mud dumping, and the area of Sanba beach continued to decrease, with the right edge receding and moving left, causing the Jinchengzhou shoal to shrink and gradually disperse.

Variation in water and sediment conditions and erosion and deposition characteristics in the reach between Three Gorges Dam and Gezhou Dam

SHI Changle, NIU Lanhua, ZHAO Guolong, DU Linxia

2020, 31(6): 875-884. doi: 10.14042/j.cnki.32.1309.2020.06.007

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A correct understanding of the variation pattern of water and sediment conditions as well as erosion and deposition characteristics in the reach between Three Gorges Dam and Gezhou Dam is essential for studying the many engineering problems in the reach. In this study, abundant water-sediment topographic data were analyzed, and the application of the theory of sediment incipient motion in erosion prediction was discussed. Owing to reservoir construction in the upper reaches of the Yangtze River and the successive operation of the two major hubs, the annual runoff in the reach was slightly reduced, the monthly average runoff was redistributed by "peak load shifting, " the annual sediment discharge declined considerably, and the water-sediment relationship in the reach was significantly changed. The cumulative erosion and deposition quantity in the reach was under short- and long-term control by the extreme hydrological conditions and scheduling of the hubs. In terms of time, there were apparent phased characteristics; in terms of space, some sub-reaches were in an active state. The bed sediment was refined and coarsened successively with the operation of the hub. The incipient critical condition curve was drawn based on Sha's incipient velocity equation, and the estimation of the maximum particle size of movable bed sediment or critical water flow of the cross-section provided a reference for predicting the possibility of riverbed erosion.

Benefit simulation of flood control project in Taihu Lake basin under extreme floods

WANG Yanyan, WANG Jing, HU Changwei, LIU Liu, YU Qian

2020, 31(6): 885-896. doi: 10.14042/j.cnki.32.1309.2020.06.008

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Flood control benefit assessment is very important for flood control project investment decision-making and disaster mitigation countermeasures. A set of integrated models and methods related to flood control benefit assessment were established and applied to the Taihu Lake basin. The set of models includes hydrological analysis methods integrating rainfall production and plain rain calculation, a large-scale hydraulic model composed of a river network hydrodynamic model and a plain regional flood analysis model, and a comprehensive damage assessment model considering the social economy and inundation factors. In this study, the flood damage of the Taihu Lake basin was simulated under extreme flood conditions. In addition, predictions of the disaster reduction benefits of different flood control projects in response to the basin-scale extreme floods were carried out. The results show that direct economic damage would be 56.829 billion RMB under the 200-year return period rainfall of the 1999 type. The flood control benefits of 30% to 100% reinforced external power would be in the range of 2.669 billion RMB and 4.570 billion RMB, followed by the benefits of new polder building and Taipu River widening. However, the benefit was merely 65 million RMB when the pump capacity of polders was increased by 30%. Based on these research results, countermeasures and suggestions, such as adding drain pumping stations along the river and the coast, strengthening the scientific dispatching of polders, and coping with risks through insurance sharing, are proposed to provide support and serve as references for extreme flood prevention in the Taihu Lake basin.

Competition and cooperation relationship of water utilization in water shortage basins: a case study of Yellow River basin

SHANG Wenxiu, PENG Shaoming, WANG Yu, FANG Hongbin, WU Jian, XU Mingyi

2020, 31(6): 897-907. doi: 10.14042/j.cnki.32.1309.2020.06.009

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It is very important but difficult to resolve the conflict between the water demand and supply in water resources management in water basins with water shortages. This study is aimed at quantifying the competition and cooperation relationship of water utilization to provide a new way to assess and optimize the relationship between the water demand and supply in water shortage basins. Herein, the excludability and non-excludability of water resources are analyzed. The competition and cooperation relationship of water utilization is then defined, and ways to quantify the degrees of competition and of cooperation are developed. Targets for the optimization of the water demand process are proposed to reduce the degree of competition and increase the degree of cooperation using the Yellow River basin as a case study. The results show that a strong competition relationship existed in reaches below Lanzhou, while the degree of cooperation was small due to an instream water shortage in the 2017 flood season. It is predicated that the degree of competition will be high in the reach from Lanzhou to Hekouzhen and the reach below Huayuankou in 2030, while inter-basin water-transfer projects can effectively reduce the degree of competition. The degree of cooperation must be strengthened by considering the ecological function of high-flow events in the flood season and the water demand of sediment transport in the non-flood season when managing water resources in the Yellow River basin. If a proportion of sediment transport water demand could be moved to the non-flood season from the flood season, the degree of competition could be reduced and that of cooperation increased.

Optimizing the moderate size using floodwater in a large-scale shallow lake

WANG Zongzhi, LIU Kelin, LIU Youchun, CHENG Liang, YE Ailing

2020, 31(6): 908-916. doi: 10.14042/j.cnki.32.1309.2020.06.010

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Storing as much floodwater as possible to meet the current and near future off-stream water demand on the premise of ensuring flood control and river ecological security, is the goal of the shallow lake floodwater utilization. For considering the uncertainties of inflows, potential water storage space and utilization patterns and determining the reasonable size of floodwater utilization, a method of combining simulation and optimization was used to establish an optimal model for moderate floodwater utilization sizes of shallow lake basins, and the model was applied in the Nansi Lake. The results shows that:① Utilization scales of shallow lakes in which utility patterns are mainly shores reverse regulation are limited by triggering water levels and capacities of pumping stations and off-stream water storage space. This limitation reflects obvious threshold effect instead of linear relation. ② The moderate size of lake basin-wide floodwater utilization is 363 million cubic meters per year and 156 million cubic meters in a flood season on a multi-year average while the pumping capacity is 48 meter per second and the trigging water level is 33.75 meters, the needed off-stream storage size is 480 million cubic meters. This study can provide a basis for the determination of the utilization size of Nansi Lake floodwater utilization and also a reference for the development of flood resources in other similar basins.

Experimental study on flow and sedimentation characteristics under the effects of low-head, run-of-river dams

YAN Zili, ZHU Dejun, DUAN Yanchong, ZHANG Peng, LI Danxun

2020, 31(6): 917-926. doi: 10.14042/j.cnki.32.1309.2020.06.011

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Flume experiments were carried out to investigate the flow and sedimentation characteristics under the effects of run-of-river dams. Based on an image measuring technique, the flow field and sedimentation characteristics were analyzed. It was observed that the longitudinal velocity of the cross-sections behind the dam had an attenuation zone on the vertical line, which decreased when there was an increase in the flow intensity. The distribution of longitudinal and vertical velocity along the vertical line of the dam crest cross-section presented significant zoning characteristics, and the zoning boundaries were almost unaffected by the flow intensity. When water depth increased at the crest of the dam, the vortex center, in the downstream of the dam, moved towards downstream and river bed, and both its area and intensity increased. The characteristics of the sedimentation morphology were very sensitive to changes in the flow intensity. At low-intensity flow, the slope of sedimentation was close to the dam body, while at high-intensity flow, no stable sedimentation was formed finally. A dynamic and stable slope entailed sedimentation in the downstream of the dam. Due to the strong vortex at the dam downstream, dynamically stable sedimentations maintain therein, and their surface profiles approximately follow the parabola law with no observable variations among different flow conditions considered here.

Effects of the opening of the deflector on the flow characteristics in the vortex settling basin

LI Lin, WANG Pingyuan, WU Yangfeng, HOU Jie

2020, 31(6): 927-935. doi: 10.14042/j.cnki.32.1309.2020.06.012

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The water and sediment separation performance of the Vortex Settling Basin (VSB) depends on the characteristics of the velocity field. To understand the influence of the opening of the deflector on the flow field, VSBs with the deflector partially perforated on the non-overflow area entirely perforated and without any openings were tested with Particle Image Velocimetry (PIV) and simulated with a large eddy turbulence model. The results showed that:① The opening positions did not affect the vortex properties of the VSBs but did affect their strength. The swirl intensity of the entirely perforated VSB was the smallest, which made it difficult to extract sediment by centrifugal force. ② The VSBs without any openings were partially perorated helped the sediment to be transported along the radial direction, move down and be discharged, but the radial velocity and secondary flow in the entirely perforated VSB were reduced, which caused the sediment to be deposited on the floor. ③ The velocity on the partially perforated deflector was the greatest, which could prevent the sediment from depositing on the deflector. Therefore, to reduce the amount of particles deposited on the deflector of the VSB and to ensure a high sediment trapping efficiency, it is better to choose a deflector that is partially perforated on the non-overflow area.

Simulation of transient mixed flows based on the exact Riemann solver

SUN Wanguang, LI Chengzhen, MA Jun, FAN Baoshan

2020, 31(6): 936-945. doi: 10.14042/j.cnki.32.1309.2020.06.013

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The Preissmann slot method is simple to simulate transient mixed flows, but it has obvious non-physical oscillation. The key to the application of this method is to suppress the non-physical oscillations. The transient mixed flows are simulated based on the Godunov scheme and the exact Riemann solver. In order to solve the problem that the algebraic identity of the Riemann problem is not smooth at the boundary of open and pressure flow, an iterative solution method is proposed. This method combines the third-order convergence method and the dichotomy method to ensure the iterative convergence to the real solution. Considering the fact that the non-physical oscillation caused by the variable space reconstruction method cannot accurately express the real physical state of the variable in space, a variable space reconstruction method based on the exact Riemann solution is proposed. This method can accurately express the spatial distribution state of the shock discontinuity in the cell, and the non-physical oscillation is suppressed from the mechanism. The case study shows that the numerical results are in good agreement with the analytical solutions or the measured values. The research results provide a new method for the high-precision numerical simulation of the transient mixed flows.

Advances in research on changes and effects of glaciers in Xinjiang mountains

XU Liping, LI Penghui, LI Zhongqin, ZHANG Zhengyong, WANG Puyu, XU Chunhai

2020, 31(6): 946-959. doi: 10.14042/j.cnki.32.1309.2020.06.014

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Identifying the changes and impacts of mountain glaciers is of great significance to the healthy and stable development of the mountain-oasis-desert system in Xinjiang. This paper systematically combs through the research results of the physical changes, chemical processes, biological resources, climate response, and ecological effects of Xinjiang glaciers. The results revealed that:① Xinjiang mountain glaciers generally demonstrated a tendency of an accelerated melting, were affected by topography and climate, and there were pronounced regional differences in the glacier changes. ② Aerosols explained the composition and source of surface material on Glacier No.1 at the headwater of the Urumqi River, and findings revealed that the glacier isotope quantified the proportion of glacial meltwater in the runoff of each basin. ③ The effect of glacier changes on the living conditions and spatial distribution of extremophiles is relatively significant, but the comprehensive feedback mechanism between the changes and biological resources is still unclear. ④ The impact of glacier melting on water resources is aggravated from the inception of the inflection point of the glacier meltwater, resulting in the reduction of ecological services and the loss of ice and snow industries. The development of unified glacier extraction standards, broadening of research perspectives, comprehensive and systematic observation of glaciers, improvement in simulation prediction accuracy, improving the technique of disaster warning, and development of countermeasures are the focus of future research on mountain glaciers in Xinjiang.

Progress in development and utilization of non-conventional water resources in China

MA Tao, LIU Jiufu, PENG Anbang, ZHENG Jintao, WANG Wenzhong, ZHENG Hao, DENG Xiyuan

2020, 31(6): 960-969. doi: 10.14042/j.cnki.32.1309.2020.06.015

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The development and utilization of non-conventional water resources have become important measures taken by countries around the world to alleviate water resource crises. To deepen the understanding of the level and status of China's non-conventional water resource development and utilization and better support its management, in this study, the terminology and implications of non-conventional water resources are highlighted and explained based on field investigations on the development and utilization of different types of such resources. In addition, the current utilization level and modes in the development of non-conventional water resources are summarized, the main problems analyzed, and targeted countermeasures suggested. In recent years, China has intensified the development and utilization of non-conventional water resources, which has increased yearly, reaching 8.64 billion m³ by the end of 2018. However, non-conventional water resources account for less than 1.5% of the total water supply in the country. Moreover, problems still exist in its operation, such as incomplete systems and mechanisms, inadequate planning and design, and shortcomings in engineering technology. These restrict the systematic development and utilization of non-conventional water resources. The development and utilization of non-conventional water resources involve a wide range of fields and a joint effort between all sectors of society is required to usher in a new era in its usage.

2020, 31(6): 970-970. doi: 10.14042/j.cnki.32.1309.2020.06.016

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2020 Vol. 31, No. 6

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