Abstract: For evaluating the accuracy of the remotely sensed precipitation products of Tropical Rainfall Measuring Mission 3B42 (TRMM) and latest-generation Global Precipitation Measurement IMERG (GPM), four commonly used error metrics (R, ERMS, EMA and ER) and four category statistical indexes (RFA, POD, B and SET) were adopted to quantify the evaluations on GPM, TRMM products by comparing with the gauged daily precipitation data obtained from the 824 meteorological stations within Mainland China. Evaluations were carried out spatially over the Mainland China and the 9 drainage basins at the daily and monthly temporal scales. The results suggested that:① The accuracy of GPM generally outperformed TRMM in Mainland China at daily scale, the R, ER and SET of GPM and TRMM reached to about 0.73, 2.03%, 0.36 and 0.70, 3.75%, 0.33, respectively; ② At daily scale, both GPM and TRMM products exhibited high detection accuracy in the Haihe River basin, the Huaihe River basin, the Yangtze River basin, the Pearl River basin and the Southeast Drainage basins, while the data accuracy in the Songhua and the Liaohe River basin, the Yellow River basin and the Southwest Drainage basins were relatively lower and the detection accuracy in the Inland Drainage basins shown relatively the lowest; ③ As the improved capability of the GPM in detecting light rainfall and solid precipitation significantly benefited the accuracy increase of GPM over Mainland China, GPM performed obviously better than that of TRMM in winter precipitation detections at monthly scale. Overall, as the successor of the TRMM, GPM outperformed TRMM over each drainage basin as well as in whole Mainland China, which implied the great potential of its application in various studies. However, yet rather poor accuracy of the GPM precipitation product in high altitude and arid regions as well as high false alarm ratio for light precipitation over the drainage basins in the Southeast China remained a challenge to improve its IMERG inversion algorithm.
Abstract: How the topography of the Yangtze subaqueous delta has evolved in response to sediment decline has aroused wide attention. In order to examine the Yangtze subaqueous delta evolution and influencing factors during the past six decades, bathymetric data surveyed in eight different years during the period of 1958-2015 covering more than 7 000 km2 of the subaqueous delta in the Yangtze River Estuary were analyzed together with the river sediment dataset of the same period using Surfer software. The results show that the overall morphological evolution of subaqueous delta in the Yangtze River Estuary went through three phases:sedimentation, equilibrium, and intense fluctuation. The decline in sediment had led to net erosion in areas with depth less than 10 m since 2009. Sharp decline in sediment supply and sediments transported from the outer estuary induced by extreme whether are the two important reasons for the dramatic change in the erosion and deposition of the subaqueous delta in the Yangtze River Estuary in recent years. The annual sediment delivered from the Yangtze River Estuary to the open seas is likely to be less than 120 million tons in the past decades, which is almost equivalent to the sediment load in recent years, indicating that the entire subaqueous delta in the Yangtze River Estuary may gradually reach equilibrium state through internal adjustment in the future.
Abstract: The spatial and temporal evolution characteristics of the Qingshuigou channel during 1976-2015 were comprehensively analyzed to investigate the long-term evolution process of the channel. A calculation method for the erosion and aggradation volumes at the Qingshuigou channel was proposed on the basis of Delayed Response Model and by considering the effects of water and sediment conditions and channel extension and retreat. Results showed that the channel reaches at the upstream of the avulsion point were eroded and then aggraded during 1976-1980. Meanwhile, the sediment deposited at the downstream channel reaches and the deposition volume increased in the downstream direction as the channel and floodplain widened. The evolution of the upstream and downstream channel reaches became in-phase after 1980. Influenced by the water and sediment conditions and other factors, the channel was eroded during 1980-1986 and aggraded during 1986-1995. Erosion occurred again due to the artificial water diversion in 1996 and the implementation of water and sediment regulation scheme. The erosion rates decayed exponentially with time after 2002. The proposed method could accurately calculate the erosion/aggradation volume of the channel for a long time period, and it might be used to predict channel evolution in the near future.
Abstract: With the impoundment of the Three Gorges Dam (TGD), the dominant discharge in the reaches downstream of the TGD have changed. Studying the changes in dominant discharge and the factors driving these changes is of great importance to illustrating the changes and mechanisms of riverbed evolution in the downstream reaches. Based on data from 1981 to 2015, the Makayev method, frequency analysis and the bankfull level method are used to calculate the pre-and post-dam dominant discharge in Yichang, Zhicheng, Shashi, Jianli, Luoshan, Hankou, Jiujiang and Datong. The results show the following:① Both the flow process and sediment transport capacity are taken into account by the Makayev method, and the results are relatively reasonable. ② The post-dam dominate discharge at each station is reduced by 3 000-6 000 m3/s and is consistent with the adjustment area changing from bankfull channel to medium flow channel, which reflects the rationality of the results. Specifically, through time, the dominate discharge decreases clearly after 2009; spatially, the dominant discharge decreases from Yichang to Jianli and then increases from Jianli to Datong. ③ The dominate discharge is sensitive to the runoff of the incoming flow and peak discharge, and this relation exhibits a positive correlation.
Abstract: To study the characteristics of bed load transport during armor breakup and reformation, three groups of long-duration laboratory experiments were conducted without sediment supply. Each experiment group employed a stepwise increasing discharge. The bed materials used were composed of a fine fraction and a coarse fraction, with diameters of 1.22 mm and 3.74 mm, respectively. Accurate and high-resolution data of real-time bed load grain size and sediment transport rates were acquired from the experiments with the help of a newly designed sediment trap. Then, the evolution of the cumulative transported mass, bed-load transport rates and the grain size of the bed load were analyzed. The results show that the cumulative mass exhibits a power function relation with time and that there are turning points along the curves during armor breakup and reformation. The bed-load transport rates are highly unsteady, and the duration of the armor formation phase is 3.5 to 20.5 times longer than that of the breakup phase. The coarse fraction and transport rate of the bed load vary with time in a similar manner. When the transport rate peaks, the coarse fraction of the bed load is equal to the coarse fraction of the bed materials.
Abstract: An inherent non-equilibrium sediment transport regime introduces autogenic processes, which can dynamically alter the base level of upstream reaches of a river. This affects safety of navigation and flood protection measures therein. An experiment has been conducted to investigate the characteristics of autogenic processes, such as:the formation mechanism, evolutional characteristics, fluctuations, and trends in a riverine environment. Wandering of depositional lobes, headward silting and erosion, channel switching, and avulsion have been observed in the experiment, and the growth and wandering of lobes controls the autogenic processes. An intrinsic threshold was found to affect the aforementioned autogenic processes. The results of the experiment showed that the critical sizes of depositional lobes, time period of fluctuations, power of headward waves, and fluctuations in upstream water-level differed with different inflow and sediment discharges. The inherent driving force and criticality of autogenic processes, and their inter-relationship with deltaic morphology, were discussed on the basis of the experimental results.
Abstract: The goal of this study is to better describe the spatial interaction that general water demand cannot reflect. Using water resource demand field, this paper analyzes the spatial characteristics of water resources demand and discusses the driving factors of water demand by combining the socioeconomic potential energy and water resource demand field. By calculating and analyzing the socioeconomic data of Guangdong Province in 2014, it was found that:① The water field intensity in Guangdong Province decreases from the Pearl River Delta region to the surrounding area. The direction of the field intensity around the center of each city is directed towards the city center. ② The superposition of the water field will change the size and direction of the city's field intensity. ③ The correlation coefficient between socioeconomic potential and water resource is 0.924. This result confirms socioeconomic status is the main driving force in the demand of water resources. With socioeconomic potential energy being the prime mover, water resources flow to developed areas and city centers. This result can assist in providing basic support for water demand prediction and management.
Abstract: To resolve the problem concerning long-and mid-term ecological scheduling of reservoir groups, the Xinjiang Irtysh river basin was selected as the study object, and a network node map for reservoir scheduling was established. Long-and mid-term simulated reservoir group and optimum scheduling model oriented ecologies were established, and the two models were solved using the self-iterative optimal simulation and improved DP algorithms based, respectively, on water balance and big system methods. Results of the study demonstrate that the obtained water supplement adequately meets demands concerning comprehensive water-resource utilization, ecology usages, and the corresponding guarantee rate. Results obtained using the optimum model when applied to ecologies existing within and outside of the Xinjiang Irtysh river, Wulungu lake, Beijiang and agricultural irrigation was observed to be better compared to those obtained using the simulated model. At the same time, the relationship between incoming water and ecological supplements was revealed, and a reservoir operation chart was drawn. Additionally, an operational equation, which passed the rationality test, was set up. Results obtained in this study bear critical significance with regards to providing long-and mid-term strategies for comprehensive utilization of water resources and protection of the ecological security for the fish habitat and valley forests and grassland.
Abstract: The method of equal volume of storage is a general operation in flood control planning and real-time scheduling in China. It uses the trial method to calculate the three parameters, i. e., the flow of storage, the initial flow before control and the duration of control. To improve this method, this paper proposes an integer linear programming model based on equal volume of storage for reservoir flood-control (RFEV-ILP). It takes the flow of storage as an input parameter, with 0 and 1 representing storing and releasing water, respectively. Additionally, it defines minimum stored water volume as an objective function, calculating the duration by setting the continuity of the water storage constraint in storing. A case studied in the Tingzikou reservoir perfectly illustrates that the proposed model is more stable and has less than 1% in flood control capacity as calculated by compensative regulation. Based on the optimization model, the numerical relationship between flood control storage and the three parameters can be deduced. It can also reveal the relationship between the flood control risk and the flow of equal volume, as well as the effects of the distance between the reservoir and flood control station on the range of flow and corresponding flood control strategy.
Abstract: Water delivery and distribution for irrigation through canals is the most important part of the internet of water (iWater). The automatic control level of this component directly affects the efficiency and risk control ability of the whole water supply system, and is of great significance for efficient management and utilization of water resources. By discretizing and transforming the integrator-delay model, discrete-time state-space model is formulated. Then optimal state-feedback controller is designed based on linear quadratic (LQ) theory and uses canal automation simulation software SOBEK along with MATLAB to test the proposed controller on the multi-cascaded canals of Changma South Irrigation District (CSID) in Gansu Province. The simulation results show that LQ optimal controller can effectively handle designed changes in water demand, stabilize the system in a reasonable time and steadily maintain the water level within the operational range, and thus the performance of the designed controller is much better than classic decentralized PI controller. In short, LQ optimal controller can effectively cope with time delays, coupling characteristics and unscheduled water intake disturbances inherent in multi-cascaded irrigation canals, and thus achieve reliable water supply service and efficient irrigation canals operation control. However, since LQ controller only uses feedback control logic, it cannot cope with excessively large unscheduled water intake disturbances effectively.
Abstract: Prototype measurements, physical modeling experiments, and numerical simulation are effective tools for studying hydraulic issues related to water conservancy and hydropower projects. To investigate the adaptability of these three methods to a new energy dissipation technology called the horizontal gyrating discharge tunnel, which is based on the Gongboxia horizontal gyrating discharge tunnel, the results obtained by applying the three methods were compared and the adaptability of the methods for different parameters was determined. The results indicate that the simulated results of the three methods are in agreement for the macroscopic flow pattern, pressure near the wall, and energy dissipation ratio. The annular cavity length of the physical models and numerical simulation are different from the results of prototype measurement, which further affects the accuracy of the hydraulic parameters in the vertical shaft section; therefore, it is necessary to correct it in engineering design. The numerical simulation and the model test are feasible methods to study gyrating cavity shape and velocity in the gyrating discharge tunnel and can effectively overcome the limitations of prototype measurement technology; further, the numerical simulation has many advantages. A 1:40 and above scale model is an effective method to study the ventilation characteristics of the ventilating shaft in a horizontal gyrating discharge tunnel. The results can be used for the selection of research methods and correction of results for this type of hydraulic issue.
Abstract: To evaluate the permeability of a coastal formation in a seawater (saltwater) intrusion area and to introduce a method to select applicable slug test models, pneumatic slug tests were implemented using a Geoprobe system at different plane positions. Layered slug tests were also performed at several test sites. The matching-type curves method was used to calculate the hydraulic conductivity parameters of formation. The results show that, if the test target formation is a confined aquifer, good results are obtained from the calculations by analyzing either the overdamped oscillation slug tests using the KGS model or the underdamped oscillation slug tests using the Butler model. If the test target formation is an aquitard, the KGS model can be used to analyze the overdamped oscillation slug tests. The calculation results will be affected by the presence of an adjacent aquifer with high hydraulic conductivity and also by the inaccuracy associated with borehole logging. If the conditions of formation have unknown permeability grade, a reasonable slug test solution model must be chosen to calculate the hydraulic conductivity parameters precisely by analyzing concurrently the layer type, the formation type, the test well structure, and the characteristics of the water level recovery.
Abstract: Aiming to study the influence of rain garden design parameter on the hydrology effect of stormwater retention, we analyzed the long-term effect of a rain garden operation using the DRAINMOD model based on an experimental study, the factors considered include the rainfall characteristics, rain garden storage depth, runoff catchment area ratio and other design parameters. The results show that, DRAINMOD can simulate the hydrologic processes of rain garden reasonably well; the continuous simulation using the long-term meteorological data (1951-2007) showed that the average volume reduction of stormwater runoff was 18.5%; the rain garden treated runoff volume accounted for 76.1% of the annual total. There was a critical value for the rain garden storage depth, above the value, increasing the rain garden storage depth had no effect on rain garden retention capacity. Increasing the runoff catchment area ratio increased both the rain garden treatment volume and the overflow volume. Adding a 30 cm internal water storage (IWS) in the rain garden decreased the subsurface drainage by 19.2%; and increased the volume reduction to 33.5%. Rain garden with IWS may promote the volume reduction and water quality improvement, producing positive effect on urban stormwater management and non-point source pollution control.
Abstract: To compare the differences in water resource consumption among hydropower projects in the Lancang-Mekong River basin, we chose 37 hydropower plants as examples. Based on an analysis of remote sensing data, the water footprints of these hydropower plants in 2015 were analyzed using the improved water footprint method. The results revealed that the hydropower plants in Lancang River basin, which have the smallest water footprint of hydropower plants in China, indicating a high efficiency of electricity production. In contrast, the hydropower plants in the Mekong River basin located in Laos and Thailand had a larger water footprint, suggesting a low efficiency of electricity production and high consumption of water resources. Therefore, from the perspective of power generation efficiency and water resources consumption, the upstream section in China is more suitable for hydropower development, and the influence of water resources consumption in hydropower should be appropriately considered in downstream countries.
Abstract: In the coastal region, the characteristics of wave asymmetry are closely related to the sediment transport. It plays a crucial role in determining the structure failure of a coastal defense due to the toe scour. However, most of the researches related to the wave asymmetry focus on the normal incident waves, there have not been sufficient researches on the evolution of wave asymmetry for obliquely incident waves. Therefore, it is necessary to investigate the evolutions of wave asymmetries for obliquely incident waves in the coastal region. In this study, a numerical model is developed to conduct the numerical experiments, which is based on the fully nonlinear Boussinesq equations. Irregular waves with incident angles ranging from 0° to 75åre simulated. The effect of incident angle on the wave asymmetries is analyzed by comparing the numerical results obtained with different incident angels. The results showed that the parameters of wave skewness and asymmetry, as well as bispectrum in the shoaling process, are moderated with an increase in the incident angle. This indicates that the degree of the triad wave interactions could be weakened by increasing the incident angle, which leads to a decrease in the nonlinear wave characteristics. In conclusion, the empirical formulae for wave skewness and wave asymmetry by combining the influence of incident angles are recommended.
Abstract: Wave attenuation by coastal vegetation has attracted coastal engineers' wide attention. This study reviews present investigations and latest advances in typical approaches in laboratory experiments as well as theoretical analysis, as well as the analytical methods on micro and macro scales. Firstly, the governing parameters in vegetation modeling and theoretical models are summarized, such as those of vegetation, hydrodynamics and experiment setup in a laboratory experiment. It is revealed that the analytical methods can be classified into method of reduction in wave height and method of dissipation of wave energy, respectively. Finally, this paper points out that the scale effect in vegetation size and wave parameters is the main reason that limits the universal applications of analytical solutions, only applicable in 2-D flows. The further problems, coupling of multiple factors such as seasonality, motion of vegetation, wave breaking, the randomness and nonlinearity of waves, tidal currents, are desirable to be addressed.
Abstract: Water demand management is attracting increasing attention within the field of water resource management. Residents are the basic water use units and are the participants, executors and beneficiaries of water demand management. Research on the rules, influential factors and mechanisms of residents' water consumption behavior serves as the micro-foundation of effective water demand management strategies. From the standpoints of sociology, economics and computer simulation of residents' water consumption behavior, this paper gives a detailed review of research progress both within China and abroad to provide a reference for related research. The investigation shows that with the development of investigation techniques and theories, sociological research on residents' water consumption behavior gradually progresses from easily measurable objective factors to subjective factors that are difficult to measure. It obtains data through latent variables and observational variables, and uses the theory of planned behavior to deconstruct residents' water consumption behavior in myriad aspects. It also uses structural equation modeling, large-scale sociological survey experiments and environmental psychology repeated behavior models to reveal the impact mechanism. Economic research on residents' water consumption behavior aims to analyze the mechanism of micro-individual behavior under the influence of economic measures. This research also simulates the change of variables through econometric models to evaluate price elasticity of demand, impact of water pricing structures and billing frequency on demand, the comprehensive impact of water regulation and price regulations on residents' water consumption behavior, and how restrictions work with regard to economic measures. Research on computer simulations of residents' water consumption behavior that focus on improving simulation algorithms of micro-individual behavior, such as agent-based models expanding to multi-agent-based models, combined with complex network theory and social influence theory, can collectively summarize water consumption at the regional scale and repeat historical water resources events and simulation of water demand management strategies to provide recommendations for assessing and improving policy. Generally speaking, relevant domestic research is still in the follow-up stage; however, the focus is on improving the applicability of research methods in light of domestic practice. Future research needs to strengthen the synthesis of analytical methods such as sociology, economics and computer simulation, understanding residents' diversity issues, and explore habits, preferences, awareness, psychology and other potential factors behind residents' water consumption behavior.