Abstract: To analyze the relationship between the urbanization development degree and extreme rainfall change, hourly rainfall data from 22 rainfall stations in the Pearl River Delta region from 1973 to 2012 were selected. Methods such as spatial analysis, linear regression, sliding average, and the Mann-Kendall trend test were used to analyze the spatiotemporal distribution and variation characteristics of extreme rainfall and rainstorm patterns in the Pearl River Delta region under the sense of high urbanization. The results showed that extreme rainfall in highly urbanized areas of the Pearl River Delta increased by 44.3 mm/(10 a), showing a significant increase in the trend, while the other adjacent areas showed no significant change. The significant increase in extreme rainfall during the first rainy season was the main reason for the increase in the annual extreme rainfall in highly urbanized areas. In addition, the rainstorm pattern in the Pearl River Delta region was dominated by unimodal patterns, among which the proportion of type Ⅰ rainstorms was the highest (approximately 33.7%). The occurrence frequency of type Ⅰ rainstorms in highly urbanized areas has increased significantly, which easily leads to an increase in rainstorm flooding events. Therefore, flood control and drainage work in highly urbanized areas should be strengthened.
Abstract: In this work, Water shortage problem is severe in the Haihe River basin (HRB). Furthermore, there is a statistically significant decreasing trend in runoff in the HRB. Quantitative assessment of the attribution of runoff change has important scientific significance to investigate the mechanism of water cycle and to support the sustainable utilization of water resources. Using regionalization approach, the model parameters of the VIC model are estimated for the whole HRB, and the natural runoff has been reconstructed. A quantitative attribution assessment framework for runoff change driven by temperature change, precipitation change, underlying surface change and water withdrawal has been constructed. The results indicates that human activities are the main reason for the runoff decrease in the HRB during 1956-2010. Generally, climate change and human activities account for 1/3 and 2/3 of the runoff decrease, respectively. In climate change, the contribution of precipitation decline (30%) is much higher than the impact of temperature increase (4%). In human activities, the influence of water withdrawal (55%) is greater than that of underlying surface change (11%). Spatially, from north HRB to south HRB, the impact of temperature change decreases, while the influence of precipitation change increases. Relatively, the breakpoint of runoff is later in the Luanhe River Basin, the contribution of water withdrawal in the north HRB and south HRB is higher than that in other regions, and the decreasing trend in runoff is slight and the attribution is uncertain in the Tuhaimajia River basin.
Abstract: To obtain a high-quality record of actual evapotranspiration (ETA) with which to investigate water cycle changes in the context of climate change, this study developed a method for reconstruction of ETA based on gravity satellite observations. The proposed method used GLDAS assimilated land surface water storage data to downscale GRACE equivalent water thickness to finer spatial resolution. Then, subbasin-level monthly ETA data for the Jinshajiang River basin were reconstructed based on the water balance during 2002—2016. Results showed that: ① The reconstructed ETA data (ETRecon) had high quality and compared well with three satellite-retrieval products, i.e., ETPLSH, ETJung, and ETMODIS; the strongest correlation was with the ETPLSH product (r=0.82) and the lowest root mean squared difference was with the ETJung data. ② Multiyear mean ETA in the study area was 410.8 mm/a with a gradient of increase from northwest to southeast. Temporally, it showed a significant upward trend during 2002—2016. ③ Seasonally, summer ETA was highest and it showed an upward trend over the study period; conversely, ETA in winter had the lowest value and it showed trivial change temporally.
Abstract: The alluvial river flooding problem in Inner Mongolia is prominent along the upper reaches of the Yellow River. Studying the scour and silting evolution of the river and the response mechanism of the floods can provide technical support for flood prevention and disaster mitigation in this river section. According to data on ice flood and scour and silting evolution, this paper produces the response relationship between a scour and silting evolution characteristics indicator and an ice flood condition change representation indicator based on formulaic calculations and related analyses. The results show that bankfull discharge, a characteristic indicator of river scour and siltation evolution, is closely related to the characterization indicators for ice flood sub-ice flow capacity and trough water storage increment. The under-ice flow capacity is about 1/5 that of bankfull discharge, and it decreases as bankfull discharge decreases. In addition, the channel detention increment increases as bankfull discharge decreases. The safety flow capacity in the main channel for ice flood control should not be less than 2 000 m3/s, and the increment in water storage should be kept below 1.4 billion m3 in the reach. The preliminary results can serve as a major guide for ice flood control in Inner Mongolian reaches.
Abstract: The Niyang River basin is the fourth largest tributary of the Yarlung Zangbo River. Affected by glaciers, snow, and frozen soil, the water cycle relationship is extremely complex. To further study the hydrological cycle process in the region, based on the climate and geological characteristics of the Qinghai Tibet Plateau, a distributed water cycle model (WEP-QTP) for the Qinghai Tibet Plateau, which includes a "snow soil gravel layer" continuum and "snow glacier" hydrothermal process simulation, was established by improving the WEP-COR model. Through the simulation of the flow process of the Niyang River basin from 2013 to 2016, it was found that the monthly flow Nash-Sutcliffe efficiency coefficients of the Gongbujiangda and Niqu stations reached 0.810 and 0.752, respectively; these values are significantly higher than the those (0.430 and 0.095, respectively) before the improvements were implemented. Taking 2015 as an example, the flow process simulated by the WEP-QTP model during the flood season, especially before the main flood season (frozen soil thawing period), does not show large fluctuations, and the Nash-Sutcliffe efficiency coefficient of the daily flow obtained from the simulation increased from-0.67 to 0.54 compared with WEP-COR. The model improved the regulation of the groundwater aquifer, making the flow process more stable and closer to the actual measurement, for use in the hydrological simulation of the Qinghai-Tibet Plateau.
Abstract: The comprehensive rainstorm formula applicable to different durations is an important basis for coordinating urban pipe network drainage and regional flood and waterlogging control. The 65-year monitored rainfall series of Xujiahui meteorological station, which was selected to be the representative rain station of Shanghai City, was collected to establish the relationship between rainstorm intensity and duration in different return periods. The rainstorm attenuation characteristics was revealed to formulate the single rainstorm formula of each return period. The long duration comprehensive rainstorm formula applicable to different return periods was explored with reference to the rain force formula, and the rainfall return period formula was derived. Results show that the rainstorm intensity attenuation index between 1 hour and 24 hours in different return periods are approximately 0.74. The obtained long duration comprehensive rainstorm formula could be used to calculate the design storm of any duration (1-24 hours) and any return period (2-100 years), and the relative and absolute root mean square error of the formula are 1.9% and 0.009 mm/min, which meet the requirements of the criterion, respectively. Also, the rainfall return period formula could be applied to ascertain the return period of any rainfall event between 1 hour and 24 hours so as to serve urban flood prevention and control decision making effectively. Notably, the research achievements have been incorporated into the local standards of waterlogging control in Shanghai City and are of significant reference value to other cities.
Abstract: The calculation of movable bed roughness plays an important role in modelling of flood routing and bed deformation in alluvial rivers. Bedforms in the Lower Yellow River (LYR) vary greatly under different flow and sediment regimes, which cause complicated variation characteristics of movable bed roughness. Therefore, it is necessary to propose a formula of movable bed roughness, in order to improve the predictive accuracy of morphodynamic models for the LYR. Based on 686 runs of measurements at seven hydrometric stations such as Huayuankou, Gaocun and Lijin in the LYR during the period 1958-1990, Froude number (Fr) and relative water depth (h/D50) were selected as the representative factors influencing the magnitude of movable bed roughness in the LYR, and then a formula of movable bed roughness based on the flow regime partition was proposed and calibrated by these measurements. Finally, the accuracy of the proposed formula was verified against 2 288 runs of measurements at these stations during the period 1991-2016. Main results obtained from this study indicate that the magnitude of movable bed roughness decreases with an increase in Froude number or relative water depth; the calculation accuracy of the proposed formula of movable bed roughness based on the flow regime partition is obviously higher than the formula without considering the flow regime partition and the existing four formulae proposed by other researchers, with the determination coefficient between the calculated and measured data at each station generally greater than 0.80. Therefore, flow-sediment conditions and bedforms play an important role in the variation of movable bed roughness in the LYR.
Abstract: The tidal flat evolution law is an important basis for protecting and developing tidal flat resources. The complex flow-sediment conditions and high intensity of human activities in Hangzhou Bay have led to complex tidal flat evolution mechanisms. The tidal flat evolution law and its mechanism on the south bank of Hangzhou Bay under the influence of flow-sediment variation and human activities in the past 60 years were analyzed based on the hydrographic and bathymetrical monitoring data of Hangzhou Bay in the period of 1959-2019, combined with the process of deposit-promoting and reclamation. The results show that the tidal flat on the south bank of Hangzhou Bay has been deposited since 1959, with a deposition rate of approximately 6.70 cm/a during 1959-2003, and increased to 12.59 cm/a during 2003-2019. Large-scale reclamation projects and the increased tidal range are the main reasons for the increase in the slope gradient of the tidal flat profile. The periodic evolution of the plane morphology of the Andong tidal flat is related to the cycle of high and low runoff, showing the increased/decreased curvature in wet/dry years. The reduction of incoming sediment from the Yangtze River has not significantly affected the deposition of the tidal flat on the south bank of Hangzhou Bay. The reclamation project is the main reason for the increased deposition rate and decreased tidal flat width of the south bank of Hangzhou Bay.
Abstract: The knowledge of backwater effects of the Yellow River expansion is crucial to the decision-making of river regulation and training works in the Yellow River. In this study, we propose a new method, translation correlation analysis, based on the spatiotemporal propagation characteristics of headward and downward erosion and deposition. Waterlevel data for 1950-1990 were used to analyze the process and extent of effects of headward erosion and deposition resulting from the evolution of the Yellow River Estuary on the channels of the Lower Yellow River. The results show that water levels in different sections of the Lower Yellow River increase overall with fluctuations and that water level variation is not completely spatially synchronized. At the same time nodes, water levels differ greatly in different sections, showing the propagation characteristics of disturbance waves. In the Lower Yellow River, downward erosion and deposition development are rapid, and it takes approximately one year for erosion and deposition disturbance waves to propagate from the Huayuankou cross-section to the Gaocun cross-section of the Yellow River, while changes in erosion and deposition are basically synchronized between the Gaocun and Aishan cross-sections. Headward erosion and deposition are relatively slow, with a lag effect. Changes in erosion and deposition in the Luokou cross-section have mainly been affected by the cumulative effects of changes in erosion and deposition in the Lijin section over the past 8 years. Headward erosion and deposition due to the evolution of the Yellow River Estuary mainly influence lower reaches downstream of the Aishan cross-section, which is located approximately 350 km from the Yellow River Estuary.
Abstract: The presence of vegetation changes the flow and thereby modifies the river bedform. This study explores the characteristics of the bedforms and their interactions with the overlaying flow through submerged vegetation. Different types of turbulent flows are generated in a laboratory flume, and the bed topography and turbulent statistical parameters are measured. Results indicate that the bed morphology is characterized by the horseshoe scour holes around individual plants and the gully-ridge pattern in the wakes. These bedform features do not significantly influence the hydrodynamics in the free shear flow. However, the horseshoe scour holes, the gully-ridge pattern and sand ripples intensify the vertical variation of the flow velocity and promote the vertical momentum exchange in the bed shear flow. Besides, the horseshoe scour holes, the gully-ridge pattern and sand ripples persist in the 'quasi dual-flow' regime. These bedforms are found to promote momentum exchange and inhibit turbulent sweeping within the canopy layer. Above the vegetation canopy, however, these bed features are found to inhibit momentum exchange and promote turbulent ejection.
Abstract: To quantify stage variations in the middle reaches of the Yangtze River that are affected by backwater effect and channel adjustments, the hydraulic characteristics of selected typical reaches were analyzed and the applicability of previous stage-discharge rating methods was studied. Furthermore, a hydrological data-based stage-discharge rating method for non-uniform flow was proposed. Results indicated that the influences of channel adjustments and backwater effect cannot be separated using stage-discharge rating methods for uniform flow. Moreover, previous rating methods for non-uniform flow were difficult to use when only stage, but not discharge, should be estimated. Although channel morphology is irregular in the middle reaches of the Yangtze River and the flow roughness coefficient varies at different discharges, evident laws for channel hydraulic geometry factors and roughness-discharge relation were observed. The momentum equation for steady non-uniform flow can be simplified on the basis of the hydraulic features of the channel to obtain the rating function between the upstream and downstream stages and discharge. By using the proposed rating method, the upstream stage can be estimated via the rating function based on long term data. Meanwhile, the residuals between the estimated and measured stages represent the effects of channel adjustments. Lastly, the proposed method was applied to three typical reaches to examine its accuracy and applicability. The results showed that the coefficient of determination (R2) between the measured and estimated stages exceeded 0.99 when the channel was not altered. Therefore, the proposed method is capable of identifying stage changes caused by channel adjustments.
Abstract: The formation and dynamics of slope runoff as karst aquifer recharge process are rarely described specially for the karst area of South China. A spring which discharge epikarst in Yaji experimental site was selected as the research point. The hydrological and hydrochemical dynamic process under different precipitation conditions were obtained through multi-parameter monitoring for a hydrological year. Understanding the dynamic characteristics of runoff formation conditions as well as water source composition of slope flow were formed using hydrological and hydrochemical analyzes. According research there are strong seasonal changes which reflected on the hydrological processes for slope runoff. The total duration of low water level is half of the year, the continuous duration is more than 3 months, and more than 40 days are continuous dry-up throughout one hydrological period. All this indicates instability and variability in slope runoff, and it is necessary to apply certain measures in regulating this process. The hydrochemical dynamics controlled by carbonate dissolution show the merging of runoff from different geological formation. The oscillation of electrical conductivity as well as other indicators show that the runoff formed in bare rock surface plays vary important role. According to the geological structure of slope area regulation through three approaches is proposed: reducing runoff leakage in bare rock area; improving permeability of the epikarst zone; exploring karst conduits in dolines. These measures will help to increase the storage capacity of water tank and improve the utilization efficiency of runoff.
Abstract: Three-dimensional instantaneous flow velocity was measured by an Acoustic Doppler Velocimetry(ADV) in a combined fishway with an overflow notched weir, and a vertical slot with an identical layout. Turbelent structures, such as time-averaged velocity, turbulence intensity, Reynolds stress, correlation function, and turbulence scales in the fishway pool were analyzed based on the jet mechanics and statistical theory of turbulence. The experimental results showed that flow patterns in the combined fishway pool of the overflow weir and the vertical slot, exhibited complex three-dimensional turbulent structures. The effects of the overflow weir on turbulence intensity and Reynolds stress were more considerable, relative to the vertical slot, especially in the pool surface layer. But correlation of the eddy structures in the weir flow region was better than that in the wall jet region, due to vertical slot. Also there were larger eddy structures in the weir flow region, whereas the eddy size in the wall jet region was smaller. Compared with the single fishway, turbulent structures in the combined fishway were more complicated. These studied results can provide an important guide for optimizing fishway design and rehabilitating fish habitat.
Abstract: A CFD-DEM-IBM method with high resolution is proposed based on the immersed boundary method (IBM) to describe the sedimentation phenomenon accurately and to investigate the underlying influence mechanism between fluid and particles in dense fluid-particle systems. The fluid phase is analyzed by the computational fluid dynamics (CFD) while the discrete element method (DEM) is utilized to simulate the motion of individual particles. The IBM is introduced to tackle the moving boundaries of particles and the interaction forces between fluid and particles are considered by an extra body force added to the Navier-Stokes momentum equation. The strongly coupled fluid-solid system is then achieved through the successive iterative scheme where several iterations are required within each time step until the convergence conditions are exactly satisfied. Sedimentations of one, two and multiple particles are simulated, which reveal that the proposed method could obtain the accurate interaction forces among discrete particles and fluid along with the fully resolved fluid phase around the particles compared with the conventional unresolved CFD-DEM method. The agreement between present results and previous work demonstrates the accuracy and validity of the presented method, and the applicability together with the superiority of the CFD-DEM-IBM method is also proved when the dense particulate flows occur.
Abstract: Sediment connectivity is closely related to geomorphology, topography, ecological hydrology, soil erosion, nutrient and pollutant movement, and water quality conservation. As one of the hot topics in soil erosion research during the past decade, sediment connectivity is required to be fully examined from the perspective of soil erosion. Sediment connectivity describes the interactions of sediment cascades between different topographical and landscape units in a system which is usually quantified with the structural connectivity and functional connectivity in four dimensions, i.e., lateral, longitudinal, vertical and temporal. Its impacting factors include climate, lithology, geomorphology, watershed characteristics, topography, soil properties, vegetation, hydrological processes, soil erosion and human activities as well as their temporal and spatial variations. The specific influencing mechanisms vary among these factors and among different spatial scales, therefore resulting in distinct responses of sediment connectivity. Field survey and mapping, graph theory, index and model simulation are frequently applied to investigate and quantify sediment connectivity. The theories behind these methods are different, so do the required data, specific procedures, and the corresponding results. The index of connectivity (IC) is the most widely employed in the quantification of sediment connectivity. Nevertheless, IC well reflects the structural connectivity, rather than the functional connectivity. From the perspective of soil erosion, future studies regarding sediment connectivity should focus on the concept, influencing factors and their dynamic mechanisms, method comparison and index optimization, relationships of sediment connectivity with hydrological connectivity, soil erosion and sediment delivery ratio, as well as the effects of soil conservation measures on sediment connectivity and the corresponding mechanisms.
Abstract: As an essential part of riverine, lacustrine, and coastal wetland ecosystems, aquatic vegetation (AV) provides important ecosystem services, and many of the ecosystem services arise as AV has the ability to alter local hydrodynamic conditions. Studies on vegetated flow are helpful not only for scientifically illustrating the environmental and ecological effects of AV but also for guiding the practice of ecological restoration and pollution regulation in rivers and lakes. Considering two kinds of hydrodynamic environments (i.e., unidirectional open-channel flow and waves), this paper summarizes the main findings on the influence of AV on flow structures and sediment movement domestically and abroad. Under unidirectional open-channel flow conditions, research on the influence of AV on hydrodynamics has mainly focused on the flow resistance caused by AV and the turbulent flow structures and scales within canopy. Related studies on waves have mainly focused on the effect of AV on wave damping and the mean and turbulent flow structures. Dominated by hydrodynamic conditions, sediment movement under the influence of AV has recently received a lot of attention on the incipient sediment motion and bed load transportation under unidirectional flow conditions and sediment resuspension under waves.