Abstract: Since ancient times, the changes of water issues have led to the transformations of water governance patterns. At present, China is confronted with multiple water problems such as waterlogging, water shortage, water pollution as well as water ecological damage, which is essentially a crisis of governance. The core of the solution to the water problem of China is the reformation of the water management patterns and then to realize water control goals. In order to break through the water-control dilemma that the water problems often rebound, we must fully learn lessons from rivers and lakes governance at home and abroad. Taking the implementation of river governor system as an opportunity, we should change the current situation of empirical, decentralized and terminal governance to the government-led approach. This has the advantage of one-party domination, multi-party cooperation, multi-rules unification, multiple benefits acquisition, technology leading, systematic management and accurate strategy implementation. In the process of water management, we should not only understand the nature and the society, but also human beings and their spiritual activities. Water science must be integrated with natural science, social science and the humanities. The fundamental goal of ecological river and lake construction will be truly achieved while the accurate concepts and the scientific patterns of water treatment have been roundly established. In summation, we should strengthen the scientific and technological guides and supports, and then carry out the comprehensive improvements of regional water problems.
Abstract: The evolution and scientific regulation of water resources in water shortage basins in relation to a changing environment is not only a key issue that is of global concern and study, but also a primary challenge China has to face in terms of water resource safety. This study aims to improve the ability of water resources allocation to solve the acute contradiction between the supply and demand of water resources in a basin affected by drastic environmental changes. The project recognized 5 key scientific issues:evolution of supply and demand of water resources, adaptive estimate, efficient sediment transport, water allocation plan optimization, and integrated dispatching. This project proposed a general framework to study the water resources optimization and comprehensive operation in the Yellow River Basin. This was done by analyzing the evolution mechanism between the supply and demand of water resources, conducting a comprehensive adaptive estimate for the water allocation plan, producing hydrodynamics condition building technology of efficient sediment transport in river-reservoir linkage, utilizing the dynamic equilibrium allocation theory of water resources, and implementing a multi-dimensional synergistic operation platform for the Yellow River cascade reservoirs. A water resources allocation and scheduling technology system was then constructed in a water shortage basin, which provided a method reference to improve the water resources management ability and comprehensive operation technology level.
Abstract: The non-stationary nature of watersheds due to changing environments has invalidated the assumption that hydrological model parameters reflecting the physical characteristics of watersheds were time-invariant. To improve the performance of a hydrological model, it is thus necessary to consider the time variation of the model parameters. In this paper, the linear and nonlinear functions of five environment-related indicators (Normalized Difference Vegetation Index, population, gross domestic production, grain production, and irrigated area) were employed to describe the temporal variation of the parameters of the two-parameter monthly water balance model to reflect the impacts of vegetation change and human activities on hydrological processes. Impacts of four different scenarios of the temporal variation of two parameters were investigated for the upstream catchments of six hydrological stations, i. e., Zhimenda, Zhangjiashan, Xianyang, Hengjiang, Danjiangkou, and Xiajiang, by comparing the model performances under different scenarios. Results showed that the hydro-meteorological characteristics of the study catchments was non-stationary during the period 1982-2006. Compared with the baseline scenario with all time-invariant parameters, the model with time-varying parameters could improve the monthly runoff simulations and provide more skillful predictions. Specifically, the Nash-Sutcliffe efficiency coefficient (NS) of the model with time-varying parameters improved by 10.3% and 8.8% in the calibration and validation periods, respectively, at the Zhimenda hydrological station. This research can provide the theoretical basis and technical support for reservoir operation and water resources planning and management.
Abstract: In order to quantitatively analyze the hydrological performance of vegetative swale facilities and optimize the value of their design parameters, the feasibility of SWMM model to simulate the effects of vegetative swale facilities on rainwater storage in urban roads was verified through simulated runoff experiments conducted by the experimental vegetative swale. The optimized design parameters of facilities were put forward through model scenario analysis, and the influence of facilities on improving road drainage standards and long-term runoff reduction was evaluated. The research results show that SWMM model has good accuracy in simulating the hydrological performance of vegetative swale facilities. For smaller rainfall return period and slope ratio, larger storage depth, vegetation coverage rate and area load ratio, vegetative swale facilities have stronger storage capacity. It is suggested that the design rainfall return period should not exceed 10 a, storage depth should be above 10 cm, slope ratio should be at least 3, vegetation coverage rate should be above 0.5, and area load ratio should be above 5%. The drainage standards of 3 a, 5 a, and 10 a can be raised to 15 a, 20 a, and 30 a respectively after simulating the use of the vegetative swale in an urban road in Beijing, and in 64 years of operation, the vegetative swale can remove almost all runoff in itself and catchment area, which can provide reference for the design and application of vegetative swale facilities on roads.
Abstract: Composite roughness is a vital input parameter for hydraulic calculations of ice-covered channels. Two general equations for deriving composite roughness coefficient in ice-covered streams, based on the principles of flow continuity or force balance, are presented in this paper. Taking parabolic, rectangular, and trapezoidal under-ice flow sections as the representative geometries, this paper systematically summarizes the assumptions (e. g., equalities of wetter perimeters, subsectional mean velocities, and hydraulic radii) used in the derivation of six formulae:those of Pavlovskiy, Einstein, Lotter, Sabaneev, Larsen and its modified form. Laboratory measurements and field observations were used to examine the performance of those above-mentioned formulae. Comparative results indicated that the modified Larsen formula had the best overall performance and therefore its use is recommended in engineering practice. The first five formulae produced relatively large errors in the prediction of composite roughness of ice-covered streams because the main assumptions of equalities of velocities and hydraulic radii are only valid for few special cases. In particular, care should be taken when using the Lotter and Pavlovskiy formulae because of their underestimation of the composite roughness in high-grade asymmetric channels.
Abstract: Zoige Peatland has important functions of water storage, carbon sequestration, and ecology. The rising or reducing of groundwater level determines the expanding or shrinking of wetland area, but the changes of groundwater hydrological process and dynamic water budget in peatland are still lack of field monitoring and studies. In combination with the meteorological data at the Hongyuan station, field in situ monitoring has been conducted in May, July, and September 2017 in a typical small watershed in the peatland of the upper Black River in Zoige Plateau. Based on the MODFLOW model, a three-dimensional dynamic groundwater movement model in this small watershed was established to simulate the groundwater movement process, and calculate the dynamic water budget and gully drainage capacity. Results demonstrated that the daily precipitation is the dominant source of groundwater recharge, accounting for 60% of the total recharge volume. Gully drainage is responsible for the main outflow of the peatland, i. e., the highest proportion of gully drainage is up to 53%, and the proportion of the evaporation loss, 26%. The drainage capacity under the condition of gullies cutting through peat layer is roughly 2.5 times higher than that non-cutting through peat layer. The groundwater level in Zoige Peatland is seasonally fluctuated by rainfall, which is rising by about 0.5 m in the rainy season.
Abstract: Pumping well water to melt ice is one of the most effective measures to resolve the ice problem for diversion power station in high altitude and cold regions. In order to investigate the water temperature attenuation process of diversion channel for pumping well water to melt ice in winter, the prototype observations were conducted at Hongshanzui Hydropower Station in February 2013 and January 2014, respectively, which verified the numerical simulation results. Based on the numerical simulation results in the RNG k-ε model, the water temperature attenuation process of diversion channel was analyzed from the point of heat flux ratio. The analysis reveals that the water temperature attenuation process included three periods:rapidly-reducing period, transitional period and slowly-descending period. Each period was influenced by different thermal conditions. In addition, the curve of water temperature attenuation followed a power function with a correlation coefficient of 0.98. Compared the water temperature attenuation processes with the changes of atmospheric temperature, the attenuation rate of water temperature significantly increased with the decrease of atmospheric temperature. The turning point of the water temperature attenuation process was at -10℃. When the atmospheric temperature was above -10℃, the attenuation law of water temperature remained consistent and was mainly influenced by the ratio of heat flux. However, if the atmospheric temperature was below -10℃, it significantly affected the channel water temperature.
Abstract: This paper evaluated the risk of reservoirs collapse caused by nature-flood-based dam overtopping using a Bayesian network. Probabilities of single and cascade reservoirs collapse were calculated for reservoirs in Sichuan Province. The analysis demonstrates that Bayesian network is intuitive and user-friendly to investigate the risk of reservoirs collapse under multiple risk sources. A same conditional dam overtopping probability magnitude of 10-6 is derived, indicating a low risk of single reservoir dam overtopping. However, the conditional probability of dam overtopping is over 0.8 when the water storage level is higher than normal, meaning there is a high probability of dam overtopping under this condition.
Abstract: Since there is no consensus about how to assign weights in Global Circulation Model (GCM) ensemble, this paper uses the Dempster-Shafer (DS) evidence theory to synthesize the following three the basic probability assignment (BPA) methods:the equal probability, the probability for statistic characteristics of the mean annual inflow, and the probability based on the relative monthly inflow variation. Then, DS evidence theory-based Adaptive Operating Rules (DS-AOR) are derived, in order to mitigate the adverse effect of climate change. The objective is to maximize the weighted average annual hydropower generation for all future scenario, and then the Simulation-Based Optimization (SBO) method is implemented to optimize the parameters of DS-AOR. The case study of the Jinxi Reservoir shows that:under uncertain future climate change, DS-AOR is an effective and robust strategy. Compared with Historical Operating Rules (HOR) and adaptive operating rules based on Equal Weights (EW-AOR), DS-AOR results in an increase in hydropower benefits by 0.76×108 kWh and 0.61×108 kWh, and an increase in hydropower reliability by 0.5%-11.17% and 3.50%-9.34%, respectively, and it performs more robustly. It is concluded that DS-AOR facilitates adaptive reservoir management under climate change.
Abstract: Under the extreme weather condition, the sediment-water mixture with high concentration that is caused by the wave would give rise to the sudden silting of the channel, and then increases the channel silting volume. Based on the field hydrological data during typhoon Malka, it establishes the three-dimensional tidal current and sediment mathematical model of the Yangtze River Estuary under the wave-current interaction, which is used to study the problem of sudden silting in North Channel. The mathematical model verifies the process of North Channel's water sediment during typhoon Malka, and the result shows that its similarity is better. By separating the wave, the writer discusses the different of sediment concentration and channel siltation under the combined action of both tide and wave flow and studies the influence of the typhoon wave on the silt of channel. The studied results show that the wave of typhoon has a great influence on the sediment concentration with the depth of -15 m in shallow water area. Meanwhile, the sediment concentration of North Channel increases gradually from the upstream to the outside and as a result it changes the distribution trend of sediment concentration as High in the middle and low in both ends of North Channel under the normal weather. The wave of typhoon has less influence to the back silting distribution of inner waterway of North Channel entrance, and the sediment deposition increases dramatically at the outer waterway of North Channel entrance. That is to say that the sudden silting of channel mainly takes place outside the North Channel.
Abstract: To examine the erosion and deposition response mechanisms to river basin sediment reduction in different areas of a tidal reach, this study investigates the Chengtong reach of the Yangtze River. The reach is first divided into two sections based on their hydrodynamic characteristics, namely the Jiangyin-Tianshenggang section and the Tianshenggang-Xuliujing section. Then, the differences between the two sections' erosion and deposition responses to river basin sediment reduction are compared by using and integrating hydrological and sedimentological data during 1950-2014 and topographic data during 2005-2014. The results demonstrate that the upstream Jiangyin-Tianshenggang section is sensitive to river basin sediment reduction and switches from deposition to erosion relatively quickly. The downstream Tianshenggang-Xuliujing section was affected by the reduced wet-season average runoff and the enhanced uplift action by tide during 1998-2004; thus, the erosion rate decreased. After 2004, the wet-season average runoff increased while the uplift action by tide weakened, and sediment from the river basin further reduced. These changes jointly led to an increase in the erosion rate. The critical wet-season average runoff, at which tidal dynamics no longer promote deposition and instead cause erosion in the Tianshenggang-Xuliujing section, is 36 000 m3/s. This is also the critical runoff threshold at which the insignificant uplift action by tide in the Jiangyin-Tianshenggang section becomes significant. At present, river basin sediment reduction has intensified the erosion of the entire Chengtong reach.
Abstract: A series of wave-flume tests were performed to study the characteristics of regular waves breaking on coral reefs, including the breaker type, breaker height, breaker position and surf-zone width. The tests were performed on the composite slope section of a reef rim at the specified conditions combined with serial wave heights and wave periods for two water levels. The test studied the criteria for differentiating the breaker types, assessed the applicability of the four breaker indexes on coral reefs with a composite slope, and provided an experience formula describing the breaker position and surf-zone width. Thus the following conclusions were drawn:the breaker types could be differentiated by the ratio of reef-edge water depth to the deep-water wave height; in the relational expressions of four breaker indexes, the correlation between the ratio of breaker height to deep-water wave height and the deep-water wave steepness was the best; the deep-water wave height and reef-edge water depth had great influence on breaker position and surf-zone width; with the increase in the ratio of deep-water wave height to reef-edge water depth, the dimensionless breaker position (the ratio of distance between the breaker point and the reef edge to the reef-edge shallow-water wave length) decreased and the dimensionless surf-zone width (the ratio of surf-zone width to reef-edge shallow-water wave length) increased.
Abstract: This paper studies the heat exchange between the tidal sediment and seawater to explore how the tidal flats affect seawater temperature. A sediment temperature model was developed to simulate the heat flux in the tidal flats based on the data measured at a southwest Korean coastal area. The model is to simulate the spatio-temporal distribution of the vertical temperature profile of sediment in the tidal flats and heat transfer between sediment and water under scenarios with different tidal occurrences. Through the modelling scenarios, the effects to the heat flux were analyzed for the impact factors such as seasons, tidal locations, and solar-tidal phases. The modeled sediment temperature well matched the measurements. A large amount of heat exchange was found between the tidal sediment and seawater, which occurred mostly during the first three hours of interactions with a maximum heat flux rate of 398.7 W/m2. Net heat was transferred from seawater to sediment during the winter months while, in opposite, net heat was transferred from sediment to seawater during the summer months. Relatively great heat exchange was found when tidal flats was inundated near noon or within three hours after noon, which can reach a value of 2.0 MJ/(m2·d). Cumulative heat fluxes decreased with reducing exposure-time rate of tidal flats. This research provides a solid background and technical supports in exploring the effects of tidal flats to the changes of the near-sea water temperature in future studies.
Abstract: Ecohydrology provides a framework to assess pressing environmental issues related to water and ecological degradation of wetland ecosystem. The ensuing discipline, wetland ecohydrology, can thus be used to promote conservation and rehabilitation programs, integrated water resources management as well as watershed-scale climate change mitigation measures. In this paper, we summarize the historical development of wetland ecohydrology using literature bibliometric analysis. We present a comprehensive survey of major research programs and key academic conferences on wetland hydrology, ecohydrology and water resources. Three developmental eras of wetland ecohydrology are broadly proposed:① the embryonic era (the 50-80th of the 20th century), ② the developement era (the 90th of the 20th century) and ③ the flourishing era (from 2000 up till now). Each area is characterized by representative research achievements; illustrating the progress of wetland ecohydrology. We conclude that future research on wetland ecohydrology will primarily focus on the study of:① multi-factors, multi-processes and multi-scale interactive mechanisms between ecology and hydrology of wetlands; ② response mechanisms of wetland ecohydrology to climate change and potential adaptive regulations; ③ coupled hydrological-ecological-social interactions and mutual feedback mechanisms of wetland systems; ④ integrated water resources management for efficient allocation of water to wetlands. Finally, given the current situation, we present preferential research areas and suggestions for future development of wetland ecohydrology in China.
Abstract: Groundwater-dependent ecosystems (GDEs) refer to ecosystems that partly or completely depend on groundwater. Research on GDEs is essential not only for understanding the eco-hydrological characteristics and processes of GDEs, but also for protecting the ecological environment and promoting sustainable use of groundwater. This paper presented a comprehensive review on the recent progress that mainly focused on the impacting factors from natural and human activities, methods of classification and identification, simulation of eco-hydrological processes of GDEs. It also discussed the issues and shortcomings in present studies and gave perspectives for future research. It was concluded from this review that GDEs were largely impacted by climate change and use of groundwater, the classifications of GDEs should be convenient for field investigations and groundwater management, the identification of GDEs should integrate hydrogeological survey, "3S" technologies and groundwater fauna sample analysis. This review has also suggested that simulations of eco-hydrological processes for GDEs need to be focused on the interactions of surface and subsurface flows, and contributions of groundwater to vegetation, solute transport and heat exchange.