Abstract: A relatively narrow and deep channel can be formed, therefor visible change in channel width can be observed, at most of cross sections due to intensive channel adjustment during a hyperconcentrated flood in the lower Yellow River. The spatial and temporal distribution of sediment deposition was calculated for overbank hyperconcentrated floods by comparison of channel width after an overbank flood with that of non-overbank flood. Results shown that 59% of sediment that would be deposited in the main channel during non-overbank floods was removed by overbank hyperconcentrated floodsto the lower floodplain or floodplain. This indicated that overbank hyperconcentrated floods can reduce sediment deposition in the main channel comparing to non-overbank ones. Based on analysis of measured data, the relationship of channel contraction ratio, ranging from 15.5% to 44.0%, at overflow sections after floods to the channel width before floods was established. Correlation between sediment volume deposited on floodplain and the main hydraulic factors during overbank flooding period, as well as their physical meanings, was analyzed. Responding function of sediment volume deposited on floodplain to hydraulic factors was determined. A threshold index of flow and sediment load for floodplain deposition and main channel reforming during overbank hyperconcentrated floods was proposed, which was between 0.025 and 0.040. This research is significant to regulation of hyperconcentrated floods in the lower Yellow River.
Abstract: The response of channel thalweg is complex temporally and spatially, so investigating the characteristics of thalweg migration is crucial to the river regime and fluvial processes in the lower Yellow River. Section-and reach-scales thalweg migration widths were calculated based on 91 observed cross-sectional profiles during the period from 1986 to 2015, in order to investigate the characteristics of thalweg migration and to identify the key influencing factor of thalweg migration intensity. It is found that thalweg migration processes were reciprocating, and section-scale migration widths in upper reach were larger than those in middle and lower reaches. The magnitude of migration widths decreased dramatically after the operation of Xiaolangdi Reservoir, and it is discovered that the thalweg migration widths in the braided, transitional and meandering reach decreased by 47%, 37%, 41%, respectively. The incoming flow and sediment regime is the dominant factor, although channel boundary conditions (such as floodplain-channel elevation difference, bed material composition) can influence the thalweg migration intensity in the braided reach. The thalweg migration intensity of the braided reach can be expressed as a power function of the previous 4-year average fluvial erosion intensity, and the empirical equation has been verified using the data in 2013-2015.
Abstract: Among all of the uncertainties of precipitation records, the gauge under catch effect is one of the most important error sources. It not only affects the accuracy of the observational value and area-averaged precipitation calculation, but also leads to a false estimate of the long-term trends of the precipitation for any sites and regions. An accurate evaluation of the gauge under-catch effect is thus of great significance for understanding long-term change of precipitation and its possible causes and impacts. Based on observational data of daily precipitation and daily mean wind speed from 20 meteorological stations in Beijing area during the period 1976-2015, the effects of gauge under-catch on precipitation records and the estimates of the long-term precipitation trends were evaluated, and the urbanization effect on near-surface mean wind speed change was also discussed. The results showed that the mean values of precipitation catch rate ranged from 90% to 95% over last 40 years, but they had a significant upward trend and a heterogeneous spatial distribution with larger catch rates in urban area than in rural area. The urbanization process, which led to a lower wind speed in urban area, was the main reason for the observed difference of the under catch rates between the urban and rural stations especially after 2006. The effects of under catch differed among years and seasons significantly. In the past 40 years, the measured area-averaged annual precipitation was 552.2 mm, while the under catch adjusted area-averaged annual precipitation was 575.3 mm, with an average absolute error of 23.1 mm and an average relative error of 4.0%. The area-averaged precipitation intensity before and after the under catch adjustment were 7.9 mm/d and 8.3 mm/d respectively. The downward trends of the area-averaged annual precipitation for the past 40 years changed from -34.4 mm/10 a for the pre-adjusted data to -37.0 mm/10 a for the aft-adjusted data. Therefore, the original observed values underestimated the daily precipitation intensity by about 4.8% and the decreasing trend by 7.0%. Larger under catch errors occurred for the more intense precipitation processes, and the inter-annual variations of the under catch effects were generally greater at urban stations than those at rural stations. There existed a clear underestimate of precipitation record for the weak precipitation process at rural sites, but the underestimate was more significant for the intense precipitation process at urban sites.
Abstract: Interpretation on the mechanism involved in the "Sun-Climate-Water" system provides scientific guidance on the water resource management. Using correlation analysis, principal component analysis and wavelet analysis approaches, the combined influences of solar activity and El Niño Southern Oscillation (ENSO) on precipitation, river flow and groundwater levels in Yoshino River basin, Japan were investigated. And the results indicate the following:① Significant influences of solar activity and ENSO on the hydrological processes mainly concentrate in the periodicities of 11 and 2-7 a, respectively. ② The solar-modulated ENSO plays a critical linkage between solar activity and precipitation/surface water resource. However, this linkage doesn't act in the Sun-ENSO-aquifer system. ③ Both direct and indirect influences of solar activity on hydrological processes in the study area are obtained. The direct influence might act via the function of non-ENSO climate indices, while the indirect influence might act via the process of "ENSO-Western Pacific Subtropical High-East Asian Circulation-Water Movement".
Abstract: As an important energy and major grain producing area in China, the Yellow River basin has had a shortage of water resources, becoming a key factor in the restriction of energy and food development. And the system risk of water, energy and food has been escalated. An overall analysis framework model of water-energy-food based on the synergetic theory was established in order to optimize the relationship between water resources, energy, and food. Further, a total partition structure model was built, also known as the water-energy-food collaborative optimization model with an inter-feedback function. The support, restriction, and interactive bond mechanism and intelligent multi-factor balancing algorithm were also studied. Finally, the integration of the collaborative optimization distribution scheme and strategy for food production, energy, and water resource utilization in the Yellow River basin was demonstrated. Results show that, by collaborative optimization and comprehensive allocation of water resources, energy, and food, the average annual water supply is expected to be 53.560 billion m3, increased by 2.398 billion m3. Both the food production distribution and energy production structure and scale are to be optimized; with an increase of 12%, per capita yield of food will reach 416 kg. Coal mining, oil mining, and total thermal power installed capacity will increase by 2.86 times, 4.08 times, and 0.80 times, respectively. According to the results, a guaranteed degree of water resources for energy development and food production security can be significantly improved, with domestic and ecological water demand given the highest priority in the model. Meanwhile, increased food and energy production can be realized, as well.
Abstract: In order to research the appearance of agricultural drought under the actual water projects, the computational method for the return periods of drought events, based on the regional agricultural water consumption, is presented in this study. Through the drought index establishment of the anomalous percentages of agricultural water consumption(WA), on the basis of drought events recognized by the drought index PA of precipitation anomalous percentages, the drought characteristic variable of the severity and duration for drought events based on WA were extracted. Meanwhile, according to the frequency distribution curves FS(x) of drought severity and the frequency distribution curves FD(x) of drought duration obtained with PA as the drought index, the return periods T of drought events based on WA were computed by use of the simplified method of Copula. Finally, combined with the return periods T0 of drought events based on PA, the formula of relationship between T and T0 was obtained through the analysis of regression. The method was applied into Bozhou city as the exemplary region for the severest influence from the drought, and the empirical relation between T and T0 was built as per all the drought events from 1975 to 2007. The results indicate:compared with T0, the severity of drought events judged by T is more consistent with the reality; there is an essential correlation between T0 and T, and the regression equation of T can be accepted as the simple estimation formula of return periods T of drought events when it comes to actual drought resistance ability of one region, and is valuable for popularized application in the process of drought mitigation and loss reduction of one region.
Abstract: Based on theoretical unsaturated soil water movement, the effects of different bioretention structural layer parameters on ponding, outflow, and runoff regulation were studied under four types of rainfall using a numerical simulation method. Based on the results, ponding was significantly affected by the depth of the surface aquifer. With increasing depth from 20 cm to 30 cm, the overflow control water was increased by about 0.196 m3, while the ponding duration increased by up to 85 min. Bioretention structural layer parameters all had some influence on the outflow of the perforated pipe. As the soil layer to sand layer thickness ratio or the internal water storage zone height increased, the outflow of the perforated pipe was delayed and the peak of the flow decreased, while the increase in aquifer depth led to the advancement of the outflow time and increase in the flow peak. Under the four types of rainfall studied, the average runoff reduction rate of the five types of bioretention ranged from 16.71% to 37.31%, the average reduction rate of the runoff peak ranged from 41.53% to 63.90%, and the average runoff delay time ranged from 97.75 min to 166.50 min. In the case of overflow, the performance of bioretention methods on runoff regulation was significantly reduced, and the effects of structural layer parameters on runoff regulation were weakened.
Abstract: A comparative flume experiment was conducted with a movable-bed model, and a prototype, to elucidate the effect of applying different similarity criteria in model sand selection on the extent of sand wave similarities. The sand wave dimensions (wave length and height) at different water levels, and flow velocities, and their variations in the forms of sand wave produced under different discharge sections, were measured to compare the similarities of the sand wave dimensions with the change of flow intensity between the two. In the test, the sand particle sizes were respectively determined to satisfy separately a sediment incipient motion similarity law, and a sediment suspension similarity law, and then to satisfy them both simultaneously. The results showed that, when the specific gravity and shape of the model were similar to those of the prototype sand wave, the model sand wave that met the similarity of incipient motion criteria was more similar to the prototypical sand wave in terms of sand wave length and height, while the model sand wave that met the similarity of suspension condition had a greater sand wave height and length than the prototype in general. The extent of sand wave similarities for the model sand wave in terms of wave height and length met both of the aforementioned similarity conditions. The different similarity laws used in model sand selection did not affect the changes in the dimensions of the sand wave with increasing relative flow intensities. Although different similarity laws were applied, sand waves in all model tests, and the prototype test, could reach the maximum sand wave height at the same relative flow intensity, while sand wave lengths increased with increasing relative flow intensity. It demonstrated that the smaller the deviation from the sediment incipient motion similarity law, the greater the sand wave similarity between the model and prototype.
Abstract: Artificial digging was accomplished comprehensively in the Loess Plateau region during summer fallow tillage period. In order to elucidate the evolution processes on erosion as well as the flow hydraulic characteristics of its complicated slope surface under the condition of continuous rainfall, this study utilizes 3-D Laser Scanner and ArcGIS. They were employed to investigate the microtopography evolution process and hydraulic characteristics under intermittent simulated rainfall, following which it offers theoretical basis for tillage practices. The results demonstrate the following:① There are three processes which are splash erosion and sheet erosion stage, the formation of rill stage and the developing of rill stage. The rill density, average depth, maximum rill length and depth increased by 1.42, 1.72, 15.57 and 3.18 times as against initial rill forming stage with rainfall. ② The initial surface roughness of artificial digging is 1.706 which decreased linearly to 1.488 with the rainfall. In the process of accumulated rainfall reaching 81 mm, the runoff and sediment yield increased slowly with the decline of roughness, but increased dramatically later. ③ The flow velocity with fluctuation increased after the rill shaping, and the flow advanced from laminar to turbulent flow speedily, but keeping the subcritical flow all the way. Under the effect of surface roughness, the flow resistance comprised of grain resistance, rain resistance and form resistance which decreased with the rainfall duration, where the form resistance took the most significant position during the entire process. The slope surface of artificial digging might have a positive impact on soil and water conservation under the rainfall intensity of 1.5 mm/min when the rainfall is within 80 mm, but it may prone to suffer rill erosion under continuous extreme rainfall.
Abstract: In order to solve the engineering problems of secondary hydraulic jump and downstream river bed erosion due to insufficient energy dissipation in deep tailwater stilling basin, this paper compares the stilling basin flow fields of flat gate pier, conventional flaring gate pier and incomplete flaring gate pier based on the physical and numerical models. Results show that through increasing velocity gradient and lateral water level gap between adjacent chambers, the incomplete flaring gate pier can promote the lateral diffusion and collision of water jets to form growing vertical vortex from bottom to surface in the upper regions of stilling basin. This would significantly intensify energy dissipation to reduce the outgoing velocity, and completely solve the common hydraulic problems in deep tailwater stilling basin.
Abstract: Nowadays the 2-D PIV is widely used in the field of fluid velocimetry. The study of characteristics of 3-D vortices detected in the 2-D PIV experiment is helpful to deeply analyze measured data and further know the fundamental turbulent physics and the fluid-particle interaction. Based on the vortex identification scheme (the swirling strength criterion), the Euler's rotation theorem and the Burgers vortex model, analytic solutions for the detection of 3-D vortex in the 2-D PIV experiment are derived. The solution demonstrates that two factors (the elevation angle made by the 3-D vortex with the measurement plane and the circulation of the vortex) influence the detection and only when the circulation value is greater than a specified value (a function of the elevation angle), the 3-D vortex could be detected. The direct numerical simulation (DNS) data of fully developed turbulent channel flow is used for the statistical analysis of that detection condition. Results show that in the 2-D PIV experiment, the higher the detection probability is, the larger the elevation angle will be. For examples, 3-D vortex tubes with detection probabilities of 90%, 50% and 10% have elevation angles of 20°, 11° and 5° respectively.
Abstract: The objective of this study was to investigate the effects of hydrology processes on the nitrogen transport and transformation in a Tibetan Plateau irrigation district. Field experiments were conducted to measure the quality and quantity of leakage within the soil and loose rock medium and the surface drainage water in the Danniang irrigation district, Nyingchi, Tibet during the hulless barley growing periods in 2014 and 2015. The lateral seepage flux and the NH4+-N and NO3--N concentrations in the soil and loose rock medium and at the outlet of the drainage canal were monitored. A procedure using a stepwise method was proposed to describe the flow and transport processes in the loose rock, and a lump first-order kinetics method was used to describe the process of nitrogen transformation during the seepage and drainage processes. The deep seepage accounted for 26.2% of the total rainfall and 40.9% of the total irrigation. The total mass of NH4+-N and NO3--N discharged into the drainage canal accounted for 20.2% and 25.1% of the total mass of NH4+-N and the total mass of NO3--N leached from the soil into the loose rock, respectively. The mean values for system errors, Nash-Sutcliffe efficiency, the relative root mean square error, and the fractional gross error between the simulated and monitored flow rates and nitrogen concentrations at the outlet of the drainage canal were 0.043, 0.694, 0.081 and 0.242, respectively, indicating that the developed method was applied successfully to simulate nitrogen transport and transformation in the seepage and surface drainage processes.
Abstract: Groundwater artificial recharge has been widely used to effectively utilize abundant rainfall in rainy seasons for managing a number of environmental problems such as seawater intrusion and depletion of spring flow caused by groundwater overexploitation. However, physical clogging (including suspended solid clogging and gas clogging) is an important factor that may negatively affects efficiency of groundwater artificial recharge. To tackle the problem of gas-clogging (i. e., a large amount of bubbles contained in artificial recharge water), an indoor device for conducting column experiments is designed. A column is filled with sand of multiple layers, and the hydraulic conductivity of each sand layer is estimated based on the Darcy's law to investigate the processes and mechanisms of gas-clogging development. The laboratory results show that, due to gas clogging, hydraulic conductivity is not a constant but a temporal function of exponential decay. The results also show that gas clogging mainly occurs in the upper layer(0-30 cm)of the sand column, and that the clogging rate decreases gradually with depth. The results suggest that, to reduce the negative effects of gas clogging on efficiency of groundwater artificial recharge, it is necessary to occasionally pause recharge and to conduct degassing during the recharging processes.
Abstract: An estuarine reservoir in northern China is characterized by intermittent inflows, continuous outflow, and dynamic salt release from sediments. We developed a quantitative model coupling water quantity and salinity, and using the proposed Muguandao reservoir as an example, examined factors that influence salinity, specifically those that cause it to exceed the standard. We also explore methods to maintain standard salinity levels in a mixed estuarine reservoir. The results showed that the cumulative effects of millimeter-scale evaporation on salinity in reservoir water are noticeable when the water level decreases. Under adverse hydrological conditions, salinity in a mixed estuarine reservoir, affected by salt release from sediments, evaporation, and water outflow, tends to exceed the standard. In contrast with the constant water level conditions, salinity increased with increasing water outflow when water levels decreased. Therefore, decreasing daily outflow could help maintain salinity standards. To ensure water quality safety, the daily available water as determined from the integration of water quantity and salinity, should factor in the management of an estuarine reservoir.
Abstract: The Modaomen Estuary has evolved from a runoff dominated to runoff-and-wave dominated estuary, since waves are now one of the important dynamic forces. However, the wave effects on the currents and floods in the Modaomen Estuary have not been studied well. A coupled wave-current model is developed in this study to consider the effects of waves on currents. The currents are simulated using a depth-averaged shallow water flow model that includes the wave radiation stresses varying with tidal level. The wave properties are calculated using the mild-slope equation, based on the water level and depth provided by the flow model. The numerical results show distinct wave induced currents and circulations in both ebb and flood tides in the Modaomen Estuary, especially around the shoals, under normal wave conditions. Because the wave propagates from the deep to the shallow water, the wave-induced currents block the ebb tide currents and the runoff. Thus, the seaward residual currents around the sand bars are reduced and the landward residual currents are increased. The wave effects cause the estuary adjustment and force the flow returning to the main channels, so that the seaward residual currents in the main channels are strengthened. The wave effects pose a threat of blocking the flood and altering the ratio of flood discharge in the main channels and floodplains. Because the annual average wave height is small, its effects are in the shallow water areas and the overall threat is limited.
Abstract: "Connectivity" in a river ecosystem originated from landscape ecology, which plays a significant role in hydrological cycle, wildlife migration, and environment improvement. Now days, from the subjects of landscape, hydrology and ecology, many definitions of river system connectivity have been delimited as hydrological connectivity, landscape connectivity, and ecological connectivity, respectively, which are characterized as natural attribution. However, due to the role of human on a river system, river system connectivity should have social attributes and its concept should be extended to cover social connectivity as well. The connotation of connectivity could be illustrated from the mechanism of longitudinal connectivity and lateral connectivity and vertical connectivity. Particularly, these interaction mechanisms are dynamic. Many quantifying methods of connectivity, such as graphic method, hydrological and hydraulic method, landscape method, biological method and comprehensive index method, have been developed. However, as all these methods have their own limitation and disadvantages, they should be suited for many problems after being modified. In advance, it could be focused on research contents, methods and techniques. In the aspect of research contents, it should be significant to extend the connotation of the connectivity and investigate the responding mechanisms to many acting factors and develop the suitable measures of recovery connectivity. What's more, it should be paid attention to the fit scales and develop new methods and tools with integrated mathematic, landscape, hydrological models with GIS, network techniques and ect.
Abstract: Based on the typical properties of coastal aquifer along with characteristics of groundwater interaction, multiphase reactive transport incorporating colloidal behaviors are presented. Specifically, this paper clarifies the mechanism of colloid behaviors driven by seawater-freshwater displacement from the macroscopic and microscopic perspectives. The findings suggest that the colloid is the link of mass transfer between terrestrial and oceanic facies. Hydrochemical variation in groundwater influence colloid transport behaviors, which are controlled by a combined effect of multiple factors. Such factors include colloid type and quantity, surface potential, groundwater pH, and ionic strength, with uncertainties of size exclusion and structural aggregation during transport. The future challenge lies within the co-transport of colloid and pollutant in the multiphase system from microscopic dimension to field scale, within which the colloid population effect during the displacement together with the aquifer sensitivity to hydrodynamic and hydrochemical conditions being the key factors. Finally, in this review, the useful foundation is put forward for long-term pollution control and resource reuse in coastal areas.