Abstract: Sponge city has become one of the hottest topics in many industries and technology fields recently, while the current construction of sponge city in China is facing a lot of controversies with different understanding on the connotation of sponge city, as well as its construction objectives, content and practical results. Considering the water problems in the process of urbanization in China, combined with the authors' research and survey experiences, this article analyzed the concept of sponge city from the perspective of urban hydrology process. Then, a discussion was made on several issues, including construction objectives and indicators of sponge city, function development, underground rainstorm storage system and construction & management institution. Finally, a summary of the related discussions was given. Key points of this paper are that sponge city is a reshape of the urban water system and the urban living environment. Integrated functions will be a presupposition of the success in sponge city construction. Urban water system including rivers and lakes are supposed to be cores in the construction of sponge city and an overall program on the basin and city scale is especially needed. The sponge city construction must base on the advantages from multi-sectoral and cross-sectoral collaborations and need to be designed systematically.
Abstract: In this paper, we predict the air temperature and precipitation of the Yangtze River basin in five years with abnormal precipitation by the Regional Climate Model (RegCM4.5). We compare the prediction results of air temperature and precipitation with three land surface parameterization schemes and two spatial resolutions. The results show that high spatial resolution can improve the accuracy of air temperature and precipitation prediction; Different land surface schemes can cause different temporal-spatial distribution of surface net flux and evapotranspiration, leading to uncertainty prediction performance of air temperature and precipitation in the Yangtze River basin. Through the comparative analysis, we found that CLM4.5 with 30 km resolution is the best combination of predicting light rain, and BATS with 30 km resolution is the optimal choice of predicting heavy rain. CLM3.5 with 30 km resolution gives the best performance for predicting air temperature in the Yangtze River basin.
Abstract: Modeling the joint distribution of hydrological drought associated with non-stationary drought properties under the effects of uncertain drought events and low flow variability is difficult. Daily streamflow data from gauging stations in Dongjiang River basin, South China are used. On the basis of run theory for truncating drought events, alterations are analyzed in terms of mean values for hydrological drought properties and their non-stationary statistics with changes in pooling and exclusion ratios. Bivariate copula functions are built for modeling the joint distribution of hydrological drought according to the test method of Cramer-von Mises statistics associated with Rosenblatt transfer. Furthermore, a pair of designed drought values for predefined joint return periods is calculated using the equalized probability method. Changes in drought properties associated with dependence and joint distribution, as well as water shortage under a changing environment in Dongjiang River basin, are investigated by comparing two subseries of droughts separated by the change point in low flow. Results demonstrate that the pooling and exclusion ratios set to 0.1 and 0.3, respectively, are rational. Despite positive dependence between drought properties, the bivariate and univariate models for hydrological droughts vary under different time series and variable pairs. The remarkable decrease in drought duration and water shortage in the middle and lower streams is attributed to the regulation of water reservoirs, particularly the Xinfengjiang Reservoir. When the joint return period exceeds the threshold by 2 years, the designed duration periods, total volumes, and daily maximum water shortage levels decrease by 63%-71%, 71%-84%, and 30%-47%, respectively. However, they still account for 12-18 d, 61.14-90.30 million, and 7.150-9.290 million m3, respectively, provided that instream flow satisfies the water demand in Dongjiang River basin.
Abstract: As the water and sediment of the Yangtze River are diverted at the three outlets into the Dongting Lake, the relationship of rivers and lakes in the middle Yangtze River is mainly determined by the changes of the flow diversion ratio at the three outlets (FDRTO). To reveal the variation characteristics of FDRTO, average daily discharge of hydrometric stations both in the Jingjiang reach and the diversion channels in recent 60 years are employed. Abnormal hydrological conditions and major human activities have been proved as the main factors induced the FDRTO changes. Besides, Reduction calculation of runoff at Yichang station considering without TGR water was conducted based on balance approach, by compared with the field data, the influence of TGR on the diversion flow can be estimated. The studies show that ① catastrophic flood and major human activities cause a 4 to 5-year trend-adjustment period of the FDRTO, the flow diversion ratio was continuously decreased during such period, and then became stable in the following balance-adjustment period; ② From 2003 to 2014, the runoff diverted from Jingjiang reach increased by 0.800 0 billion cubic meter every year under the low compensation operation of TGR in dry season, but decreased by 2.900 billion cubic meter every year effected by impounding water of TGR after the flood season. The comprehensive influence of TGR on the diversion flow of the three outlets is about 2.100 billion cubic meter every year, accounted for 4.29% of its total annual runoff.
Abstract: In order to explore the inherent law of slope flow structures under vegetation, we systematically researched, by testing via artificial vegetation simulation, the influence of submergence on the kinetic characteristics of slope flow in conditions where the vegetation is submerged or unsubmerged. According to the research:given the same gradient, both the average flow velocity and Reynolds number have a positive correlation with the degree of submergence; under flexible vegetation, slope flow changes from slow to rapid as the degree of submergence increases, the overall resistance coefficient drops with the increase of submergence degree; while under rigid vegetation, slope flow always remains slow, the overall resistance coefficient varies in a curve like single hump, the degree of submergence is 0.9 when the resistance coefficient peaks. The influence of submergence on the relative friction velocity is opposite to that on the resistance coefficient, the coefficient of determination of an empirical equation for calculating the resistance can be more than 0.97 based on the degree of submergence; the influence of submergence degree on hydrodynamic parameters is dependent on the slope gradient, so for conservation of soil and water on slopes, appropriate vegetation heights should be determined according to the slope and water depth of hilly regions.
Abstract: The sand in a natural riverbed is usually non-uniform and is considered as the basis for simulating and forecasting the evolution of the natural riverbed, to accurately understand the movement of non-uniform sediment particles. In this study, a flume experiment with non-uniform bed load movement was conducted under uniform flow condition. The particle size range of the bed material was 0.10-20 mm. The motion process of sediment particles over the rough bed was filmed using a high-speed camera mounted on the top of the flume, and basic motion parameters such as motion trajectories, velocity, and motion/rest time of the non-uniform bed load were obtained. The particle size range of the bed load was 0.74-8.19 mm. The results showed the following:the motion direction of bed load is changed by aggregates or large particles on the non-uniform bed surface when compared to results of uniform sediment; the longitudinal velocity decreases and the transverse velocity increases on non-uniform bed load; the longitudinal velocity of bed load follows an exponential distribution, the single velocity meets Γ distribution, the transverse velocity and bed load velocity vector angle meets the normal distribution.
Abstract: Bed load transport is closely connected with the turbulent structures of open-channel flow. Studies on the interaction between the movement of sediment particles and flow turbulence are of essential significance to both fluid mechanics and river dynamics. Flume experiments with low equilibrium transport of uniform sediment at different flow conditions were conducted to study the mechanism of interaction between turbulence and sediment movement. The motion of particles on the whole bed were identified by examining the gray difference between the two successive images. Analysis of the measurements yields the following findings:① Influenced by the transverse distribution of flow intensity, the probability for sediment movement was symmetric transversely, reaching its maximum at the center and decreasing gradually toward the side wall; ② Under the influence of turbulent coherent structure, particles accumulated at the region of low-speed streaky structure and were scoured at the region of high-speed streaky structure. The probability for sediment movement exhibited high-and low-speed streaky regions alternatly in the z direction; ③ The increase of friction Reynolds number led to an increase in the interval of the nearby high sediment transport rate regions, ranging from 0.13 to 0.24 times as the width of flume; ④ Under different flow conditions, the values of D/H remained 2, which corresponded to the conceptual model of streamwise vortex, indicating that the structure of streamwise vortex was an important factor to the formation of the alternating concave and convex sediment structures.
Abstract: For understanding the issue of retrogressive erosion induced by excessive sand excavation on riverbed, including the influential factors, migration and prediction method, this paper provides a numerical model which is based on a set of equations consisted of the one dimensional Saint-Venant equation, the bed load transport equation, and the Exner equation under clear-water conditions. The MUSCL-Hancock method, a type of TVD (Total Variation Diminishing) scheme, was used to distinguish the governing equations with space-time second-order accuracy. The finite volume and finite difference methods were used separately to determine the water-flow and Exner equations to speed up computation. The model was validated by laboratory experiments which were also used to investigate the erosion process. Results show that erosion rates appear high in the early scour stage, and the retrogressive length at the early 30% time reaches to 80% of the equilibrium retrogressive length. The erosion rate increases significantly as inflow intensity, headcut height and hydraulic drop increase. The linear increasing ratio of equilibrium retrogressive length to flow discharge is 0.8 which is higher than that to height of hydraulic drop. The maximum erosion depth is approximately half of the height of headcut. Once retrogressive erosion occurs, it develops rapidly and depends on inflow intensity and height of the hydraulic drop. When considering reasonable water-sediment interactions the present model can accurately and quickly predict the erosion process.
Abstract: In order to accurately identify sediment sources in the gully and hilly zones of the Loess Plateau, this study was used a composite fingerprinting method that was based on two types of fingerprint factors (14 physicochemical properties and 23 biomarker properties (n-alkanes)) with source samples and sediments derived from check dam. The results showed that, neither the individual physicochemical properties nor biomarker properties cannot effectively identify sediment sources. The physicochemical properties were showing the limitation in identifying forest and cropland, and the n-alkanes were showing the limitation in identifying the gully. However, the optimum composite fingerprint consisted of three physicochemical properties and three biomarker properties (CPI, Ca, TP, C20, C29 and Fe) could correctly distinguish 90.5% of the samples. The results showed that in the study area, gully was the main sediment source in this catchment, reaching 60.8%, while the cropland contributed 20.7% of the sediment, and forest and grassland contributed 11.3% and 7.1%, respectively. This research demonstrates that using the composite fingerprint consists of traditional fingerprint properties and biomarkers to identify the sediment source are more accurate, it would be suitable for the area where the geologic variations of a study area are small. The study is meaningful for designing sediment management and soil erosion control strategies in Loess Plateau.
Abstract: Qiandao Lake water diversion project will change the runoff process of the Fuchun reservoir and the salinity of Qiantang River estuary. A two-dimensional numerical salinity model which including tidal bore's action is established. Based on tide and salinity testing, the distance of saltwater intrusion and the exceeding period of important water inlets caused by the project are calculated. Results showed that, it will be significantly effected in the low flow year by the current scheduling scheme, the distance of saltwater intrusion is increased 3 700 meters and time available for water inlets time along the river is shorten 0.2~3.6 days, but it is little effected in normal and high flow year. In order to reduce the influence of the salt water intrusion which happened due to the project in low flow year, a reservoir optimal operation is necessary.
Abstract: Taking the typical main canal of the middle route of South-to-North Water Transfer Project as an example, the numerical simulation of sudden soluble water pollution in complex channel is carried out. First, the rapid prediction formulas of characteristic parameters (i. e., peak transport distance, pollutant longitudinal length and peak concentration) are presented based on numerical simulation, mathematical induction, and statistical analysis method. Then the rapid prediction formulas are verified by demonstration project. The results indicate that:① The peak transport distance and the add value of pollutant longitudinal length is decreasing with the channel velocity decreasing, but the peak concentration is increasing with the channel velocity decreasing; ② The relative errors between physical model test, numerical simulation and measured results are less than 15%. The rapid prediction formulas can provide decision support for managers making emergency control measures.
Abstract: Based on the latest research both on the mechanisms of river ice and on the theories of hydrodynamics, river mechanics, thermodynamics, river ice hydraulics, and mechanics of solids, this study developed a synthetic and dynamic mathematic model of river ice for the Baishan reach of the Songhua River (China). This model incorporates hydraulic, ice transport, thermal, and ice components, and the equations of the model are solved numerically using a finite difference method. The presented model was validated fully against 15-year series of comprehensive field observations including geomorphological, meteorological, hydrological, thermodynamic, and ice regime data, and the calculated results agreed well with the measured data. This study revealed that the Dawaizi reach, which is 4 km downstream of the Baishan dam, freezes first, and then the front of the ice cover progresses gradually upstream. Furthermore, the shape of the accumulated frazil ice on the underside of the ice cover is similar to that of the longitudinal profile of the riverbed in the Baishan reach. The presented results will be of value to studies of both river ice and ice damage control in northeastern China and in other cold regions.
Abstract: The purification effects and suitable operation conditions of bio-swale on urban road runoff are investigated through experiment and simulation. Two types of bioswale system were designed:one with semi-permeable substrate, and another with impermeable substarte. Each type consists of 5 bioswales with different typical media. The experimental conditions were selected through multi-level orthogonal test with different influence factors and single-factor analyses. The results show that media combination is the most important factor affecting the overall treatment effect. The bioswales achieved the best purification effect with fly ash mixing sand as the media, and the overall removal rates were 83.12% and 73.18% for the impervious and semipermeable types. The optimal submerged zone height was 150 mm. Multiple regression models among the pollutant (TN, TP) removal rate, discharge rate and operation factors were derived with high determination coefficient (R2) and Nash-Suttcliffe coefficient. The Hydrus-1D model was then used to simulate the TP vertical migration in the bioswale under three influent concentrations. The mean relative errors of effluent concentration between simulated values and measured data were 14.11%, 17.33% and 26.57% respectively, indicating good modeling results.
Abstract: According to the requirements of National Action Plan for the Prevention and Control of Water Pollution, rational treatments of subbasin, subregion and substage water sources should be established in the critical watersheds to promote their environmental management based on the control units in the 13th National Five-year Plan. We developed a unit dividing method combining the county administrative boundary and watershed management, integrating natural water characteristics and three-level zoning of water resources. In addition, the factors of pollution distribution, socioeconomic factors, and land use were also considered. Based on the method, the major basins of China are divided into 1784 control units, which facilitate the issue of 343 national control units by Ministry of Environmental Protection. As a result, the water quality need is improved in the 13th National Five-year Plan in June 2016. We hope the method can provide scientific rationale and technical support for the accurate and differentiated watershed environmental management based on control unit with clear responsibility for the local government during 2016-2020.
Abstract: In order to protect aquatic system health of Wujiang River and achieve the win-win goal of the water energy resources development and ecological environment, the ecological operation of cascade hydropower stations along Wujiang River in Guizhou provience is studied. The minimum, suitable and ideal ecologically flow demands of the Hongjiadu, Wujiangdu and Silin stations were analyzed. And the multi-objective combination optimization scheduling model of Cascade Hydropower Stations there was built and solved. Mean annual and typical year generating capacity of 9 reservoirs are calculated. Ecological water period guaranteed rate and the scheduling process of 3 main control sections are showed. The results show that this study can increase the ecological water period guaranteed rate of Wujiang River, as well as guarantee benefits of flood control and power generation. As for low flow year, it is hard to reach the ideal ecological flow demand.
Abstract: Under the global change, water crisis was identified as the most critical issue of the world crisis in the coming 10 years. The topics of most concern in the water crisis are the transboundary water dispute and its geo-cooperative competition in international rivers. Many scientific and technical problems need to be solved for transboundary water security and benefit sharing. In this paper, the research progress of water security and water benefit in international rivers were reviewed, and their problems and challenges identified. Focusing on the establishment of theories and methods for transboudary water benefit sharing adapting to the global change, the key scientific and technical problems, and the innovative approaches were proposed; the major objectives and contents, and the general scheme and technical routes for multi-discipline researches, have been set. These researches will facilitate the development of water science of international rivers, and strengthen the capacity building to governance the transboundary water risks under the global change.
Abstract: In order to meet the significant demands of enhancing our interdisciplinary research ability and protecting the national interests in the field of global change and response, this research is to focus on the evolution of atmosphere-land surface-hydrological processes in the context of global change, and to integrate the new disciplinary theory and technological progress in meteorology, climatology, hydrology, water resources, and system engineering. According to the technological scheme of mechanism recognition-law understanding-situation diagnosis, researchers will publish the global terrestrial gridded data of generalized water resources and water cycle flux of spatial resolution, streamflow and flood events of river channels from 1st order through fourth order in the past sixty years, by taking long series of highly-dense prototype observation, multi-scale mechanism experiment, numerical simulation with physical mechanisms and geographical information technology as a key support, and making full use of the functions and advantages of cloud-platform storage, computing and management. The outcomes of this research project would provide an important foundation for China's participating in global climate negotiation and international climate governance, and implementing national strategies, such as ‘the Belt and Road Initiative’, so as to produce a remarkable socioeconomic benefits.