Abstract: This study evaluated the accuracy and consistency of TRMM rainfall at basin scale across China over the period of 1998 to 2013 based on gauged daily rainfall from 2 257 meteorological stations. The detection accuracy indices (POD, FAR, ACC, and CSI), Pearson correlation coefficient (PCC), and relative error were used. The results show that: ① Detection accuracy of daily TRMM rainfall events decreases from southeast coast to northwest inland in general; ② Average annual rain days from gauged rainfall is significantly larger than that of TRMM; ③ There is a good relation between monthly/annual gauge rainfall and TRMM rainfall at all stations, except for the stations in Northwest China; ④ Average annual rainfall estimated from TRMM is higher than that of the gauged rainfall in all basins, especially in the Southwest China. Relative error of monthly areal TRMM rainfall is smaller in the rainy season and larger in dry season; ⑤ Trends of annual areal TRMM rainfall is in agreement with that of annual areal gauge rainfall in all basins. Annual rainfall demonstrates a decreasing trend in the basins in southern China, and an increasing trend in the basins in northern China. As a result, the annual rainfall overall China shows a slight decreasing trend from 1998 to 2013.
Abstract: The river network flow concentration parameter Cs of the Xin'anjiang model is mainly controlled by topological and geomorphological characteristics of the river network. In order to address the issues of Predictions in Ungauged Basins (PUB), we developed a physically based method to estimate the values of Cs in ungauged basins from the numerical solutions of the partial differential equations with proper definite solution conditions, which describe the dynamic changes of flow concentration processes of the river network. This method can be easily applied to the ungauged basins. To evaluate the robustness and effectiveness of this method, we applied it to derive the Cs values of the Xin'anjiang model and calibrated the Cs parameter directly in 25 humid and semi-humid basins in China. The results show that both derived and calibrated values were comparable to each other in general. Regardless of whether the catchment was divided into sub-catchments, the proposed estimation method was applicable. Although the model simulations using the estimated Cs values were slightly poorer than those using calibrated Cs values, these simulations were within the range of acceptable errors and satisfied the flood forecasting standard. Additionally, using the estimated Cs and recalibrating the other parameters further improved the accuracy of resultant simulations. By adopting this method, the Cs value can be obtained in the ungauged basins and makes it easier to apply the Xin'anjiang model in the ungauged basins.
Abstract: In order to explore the influence of the rock interbed on downward soil moisture infiltration, indoor soil column infiltration experiments were conducted to examine the relationship between 2 different gravel particle sizes (10-20 mm and 20-76 mm) and 5 different gravel contents (0%, 10%, 20%, 30%, and 40%), as well as the cumulative infiltration, infiltration characteristics, and the process of the wetting front. The Horton equation and Philip formula were used to verify the variations in the infiltration characteristics, and the power function was used to simulate the wetting front during the infiltration process. The results showed that: ① The cumulative infiltration becomes smaller with the increase in the rock content of the gravel particles of the same size. For particle sizes between 20 mm and 76 mm, the obstructions to the cumulative infiltration were similar above 20% of the rock content. ② The initial infiltration rate, average infiltration rate, and steady infiltration rate showed an obvious decline, along with the increase of the rock content. The initial infiltration rate of the larger-sized gravel particles is greater than that of the smaller-sized gravel particles. ③ There is a negative correlation between the size of the gravel particle and its obstruction to the wetting front. ④ The Horton equation's validation results of the infiltration characteristics were superior to those derived from the Philip formula; the power function had a good fitting result for the elapsed distance of the wetting front over time in a soil-rock mixture.
Abstract: Long-term soil water data monitored in deep loess profiles under different land use patterns, combined with the hydrogen and oxygen stable isotopic tracer techniques, were used to investigate the effects of land use change on groundwater recharge in the Changwu Loess Tableland. Results showed that: ① Both piston flow and preferential flow coexisted in the process of groundwater recharge. The land uses, in order of decreasing the groundwater recharge by piston flow, are the fallow land, low-yield filed and high-yield field. ② The increased productivity and large scale conversion of cropland to apple orchards have resulted in reduced groundwater recharge by piston flow, combined with the increased groundwater mining, causing the groundwater table to decline continuously at 0.3 m/a. ③ The isotopic data indicate that preferential flow is currently the main path way for groundwater recharge. In order to achieve effective supply and sustainable utilization of groundwater resources on the Loess Tableland, it is necessary to regulate the land use structure reasonably and maintain an appropriate level of land productivity.
Abstract: Gullies are pervasive topographic features on the Loess Plateau. We selected two typical gullies in the water-wind erosion region of the plateau to study the effect of gullies on the spatiotemporal variability of soil-water. The distribution and variation of soil-water storage were evaluated using time-series analysis and classical statistical methods. Soil-water storage varied with distance to the gully borders. The spatial average soil-water in the study sites was 300 cm from the border. soil-water in the vertical direction was mostly dependent on the vegetation, and the gullies had little impact. The spatial distribution of soil-water at a slope scale presented different patterns. Strong upland winds increased the evaporation of soil-water, which rapidly dissipated. Soil-water storage at mid-slope near the gullies was as high as 949.9 mm. The bottom of the slopes had soil-water deficits of 4%. Soil-water storage was much higher in an apricot orchard than in shrubland dominated by Caragana korshinskii Kom. Soil evaporation, vegetation type, and the gullies increased the complexity of the pattern of soil-water.
Abstract: Coarse sediment movement in rivers is one of the key factors in causing changes in channel characteristics. The duration of the 2012 flood in the Inner Mongolia Reach of the Yellow River (IMYR) was the longest and the peak discharge was the biggest since 1989. The aim of this study was to investigate the impact of the movement of coarse sediment during the 2012 flood on the riverbed of IMYR, a coarse sand reach. The wide valley reach of IMYR is bounded by the Bayangaole, Sanhuhekou and Toudaoguai gauging stations from upstream to downstream. The coarse sand in the channel is one of the most important factors impacting riverbed erosion and deposition. Using real observational data, we analyzed the water and sediment characteristics of IMYR during the 2012 flood. By calculating sediment discharge of the bed load and comparing the river bottom of the fixed sections during the flood, this paper assesses the effect of the movement of coarse sediment on the river bottom adjustment. The results show that, ① the coarse sediment was scoured in the upstream part of the IMYR and deposited downstream during the flood in 2012; ② the open area beneath the fixed low water level followed the rule of scouring during the flood rising period and deposition during the flood falling period; ③ the open area under the low water at Bayangaole and Sanhuhekou gauging station expanded by 19 m2 and 29 m2 respectively, while the same at Toudaoguai gauging station decreased by approximately 100 m2. Owing to the imbalance of coarse sediment ejection after the flood, the actual elevation of the riverbed bottom did not get lower, and the flood risk remains at a similar level.
Abstract: Spatial heterogeneity is a basic characteristic of soil moisture and hydro-physical properties. We applied geostatistical approach to assess the spatial patterns of soil moisture and hydro-physical properties to identify the distribution and variability of surface soil (0-10 cm) moisture, bulk density, and maximum and minimum water capacity and their relationships with land use changes. The surface soil moisture, soil bulk density, and maximum and minimum water capacity displayed a strong spatial autocorrelation (spatial autocorrelation coefficient >0.87). These parameters showed similar spatial distribution patterns, changing gradually from the upperstream to middle and downstream watershed. Land use changes had a significant impact on the quantities and horizontal distribution patterns of surface soil moisture and hydro-physical properties. With respect to temporal factors, land use change and random distribution of sampling effects, the spatial autocorrelation of surface soil moisture was controlled more by random factors than autocorrelation factors. This resulted in its spatial autocorrelation to be less than other surface soil hydro-physical properties. This information would be useful in spatio-temporal soil moisture modeling and prediction and vegetation rehabilitation of degraded ecosystems in Lijiang River watershed.
Abstract: Step-pool is a controlling river bed form which frequently develops in mountain streams. Sediment transport significantly affects the stability of step-pool system by dislodging the keystone with large grain collision. The keystone of an individual step-pool was selected as the object for collision force analysis and the grain impact was quantified to add into the theoretical model for individual step-pool stability, which was then utilized for the analysis of critical conditions and the failure mechanism. The grain impact is positively correlated with grain size, grain initial velocity and the downstream scour of the step. The critical discharge for step-pool failure largely decreases under collision and larger grain size leads to the smaller threshold. The critical discharge would experience a decrease of over 50% if η > 0.55 (η=D1/D, where D1 is the diameter of the impacting grain; D is the diameter of the keystone), indicating that the large grains in bedload have a significant influence on the stability of an individual step-pool. When a flood event with long return time, landslide or debris flow occurs, the collision between the large grains and the step would enlarge the driving torque and reduce the critical discharge, resulting in much easier access to the failure of an individual step pool. This model could effectively evaluate the step-pool stability precisely when applied to step-pool reaches.
Abstract: Retrogressive erosion is a special phenomenon of fluvial processes, where the channel scour develops from downstream to upstream. Retrogressive erosion occurs due to the rapid reduction in water level, which is closely related to the engineering controlling conditions, water and sediment conditions, scouring time and duration, and initial reservoir conditions. Various impacts of destruction degree of a sandbar in a tributary on the retrogressive erosion in the main stream have been investigated. By use of a physical model for the Xiaolangdi Reservoir, which was constructed based on the similarity laws of sediment-laden physical reservoir model, four tests were conducted to investigate the effect of retrogressive erosion due to lower the pond water level quickly. On the constrain of different sandbars evolved in the tributary of Zhenshui, different flow processes and quantities from the interior tributary caused different sediment processes and quantities of the main stem channel below the branch. Restoration efficiencies of reservoir storage capacity for test 1 to test 4 was 11.6%, 6.8%, 12.2% and 6.6%, respectively. More water quantity would be released from the tributary for a severer sandbar destruction degree, which led to a higher restoration efficiency of reservoir storage capacity due to a larger volume of channel scour. In addition, a lower base level of erosion could produce the similar effects. When the volume of reservoir deposition reached 4.2×109m3, the scour effect of retrogressive erosion by lowering the pool level would be better than the case with the volume of reservoir deposition of 3.2×109m3. The results show that the calculated results are in close agreement with the experimental data. The formula for calculating the daily volume of retrogressive erosion has been improved, which was originally proposed by Tsinghua University and Northwest Institute of Hydraulic Science of China. The resulted from the improved formula indicate that a larger water volume released from the tributary could cause a higher amount of channel scour in the main-stem channel below the branch, and the calculations would be in close agreement with the measurements. These results can be used in comparing various schemes of water and sediment regulation of the reservoir in a sediment-laden river. Those enrich the subject content.
Abstract: Since the operation of the Three Gorges Dam (TGD), sediment deposition occurred primarily at the wide and curved reaches in the permanent backwater region, while no deposition occurred at the gorge reaches. Based on the measured data, sediment carrying capacities were calculated during the Pre-TGD (2001) and Post-TGD (from 2003 to 2011) period, indicating that the sediment carrying capacities decreased gradually due to the rising of the water level after the impoundment, and the deposition ratio increased step by step. The sediment carrying capacities at the wide reaches reduced greatly to the values smaller than the sediment concentrations, thus deposition occurred. While the reduction of the sediment carrying capacities at gorges was relatively small, and the sediment capacities were still bigger than sediment concentrations, no cumulative deposition happened consequently. The bigger the flow discharges, the smaller the sediment carrying capacities at the wide reaches were than the sediment concentrations, but the opposite at the gorge reaches, demonstrating that deposition at the wide reaches occurred mostly during the flood season and erosion occurred at gorges. Because of the flocculation and big erosion resistance of the fine cohesive particles, the best estimation of deposition amount was obtained when the recovery saturation coefficient was 1 for deposition and 0.01 for erosion. The estimated sedimentation at the curved reaches didn't agree with the measured values, indicating that the flow velocity had two-dimensional characteristics, and the one-dimensional sediment carrying capacity was not applicable for calculating the deposition at the curved reaches.
Abstract: Non-equilibrium sediments transport near the submarine pipeline results in local scour, thus endangering the operation of the pipeline. To investigate the sorting of sand grains in local scour hole under regular wave action, an experimental study is performed in the wave basin. The 1:15 slope with prototype sand, the median diameter of which is 0.219 mm, is tested against waves coming at 45 degree. The experimental results indicate that the evolution of the scour width, as well as the scour depth, can be divided into two stages: the primary stage and the secondary stage. The highest degree of bed coarsening is found to occur behind the pipeline rather than under the pipeline; bed coarsening grows with the increase of wave period, that is, the sand in the scour hole, compared with initial sand bed, will be refined under action of the short-period wave and coarsened by the long-period wave. However, the relationship between the wave height and the perturbation of bed sediment is not significant.
Abstract: In order to modify the spillway structure of a check dam and specify the geometry parameters of the spillway, the debris-flow pattern, scour depth, and energy dissipation were discussed under the conditions of different bottom surfaces and lateral contraction ratios based on physical modeling experiments. According to the buried depth design criteria for check-dam foundations and critical equilibrium for nonviscous particles under water, the rational value of the lateral contraction ratio was also discussed. The results indicated that the scour hole with deep scour depth was near the dam foundation when the spillway surface was a plate or curved surface with a large inclined angle. When a curved surface with a horizontal outlet was considered, not only was the scour depth decreased to some extent, but the distance between the plunging point and the dam toe was also enhanced. Generally, upon increasing the lateral contraction ratio, the energy dissipation rate increased due to the stronger interaction between the debris flows and erodible bed downstream if the debris-flow scales and spillway curvature were fixed. When the lateral contraction ratio was in the range 0.2-0.6, the scour depth behind the check dam satisfied the engineering design. Meanwhile, the distance between the plunging point and the dam toe was reasonable. This study can provide some reference points for the design of debris-flow mitigation in the engineering of check dams.
Abstract: Taking a channel downstream the Sheyang sluice as a prototype, a two-dimensional generalized morphodynamic model is established to investigate the siltation mechanism of a typical channel downstream floodgate in muddy coasts, China. The influence of runoff on hydro-sediment dynamics, as well as the souring and silting evolution in the channel, has been explored with and without considering the change of annual runoff distribution, respectively. A semi-empirical equation describing the relation between the equilibrium discharge and the ratio of runoff volume in flood season, channel averaged cross-section, offshore tidal range, tidal wave deformation, channel length and other related factors is established. For a particular channel which is practically in dynamic equilibrium state of erosion-siltation, the above-mentioned equation can be simplified as a simple form of expression of equilibrium discharge and channel averaged cross-section. And the simplified form of this formula is validated by observational data.
Abstract: The joint distribution and the risk probabilities of three variables (flood peak, flood volume and flood duration) were analyzed to provide reference for water conservancy project planning and risk assessments. Using the flood data of Gaoyao hydrologic station at Xijiang River in Pearl River basin as an example, the primary return periods and secondary return periods of trivariate flood joint distribution and the most likely design quantiles were computed by using the asymmetric Archimedean M6 Copula and the Kendall distribution function. The main conclusions of this study can be summarized as follows: comparing the risk probabilities of trivariate flood events among the different design flood return periods, the ‘OR’ primary return periods showed higher risk probabilities and the risk probability of ‘AND’ primary return periods were lower, while the secondary return periods more accurately depicted the flood risk probability under specific design frequencies. The estimated flood design quantiles of the trivariate ‘OR’ primary return periods and three variables with the same frequency were obviously higher than that of univariate floods. The most-likely design realization of the secondary return periods can serve as the new selection for the safety and risk management of flood control projects.
Abstract: In order to promote the development of socio-hydrology research and its application in basin water resources management, it is necessary to carry on a stage review of the researches and studies on socio-hydrology in recent years and recommend future research directions. The paper firstly introduces the establishment of socio-hydrology from the development of hydrology and explains its concept and connotation, then analyses the differences and similarities in content, method and theory between social-hydrology and traditional hydrology, eco-hydrology and hydro-economics; after that summaries the research progress of social-hydrology. The institution, policy and culture have been strengthened in the hydrological researches and some preliminary and exploratory researches have been carried out in case basins, however most of these studies were still based on either traditional hydrology, co-evolution or water resources management, the theory and method of socio-hydrology has not been fully developed. The following research actions are recommended for the future development of social-hydrology: strengthening quantitative research of its societal part, developing the process, historical and comparative socio-hydrology by historical analysis and hydrological reconstruction, and existing case studies; investigating the driving forces of the societal and hydrological systems to explore their dynamic mechanism; introducing the nonlinear dynamic theory to depict the complex feedback mechanism of the coupling human-water system, improving the generalized mathematical expression of the socio-hydrology; and promoting the application of the "big data" and knowledge mining technology in socio-hydrology research.
Abstract: Sandbars are the main morphological features of many wave-dominated sandy coasts and their dynamic behavior can serve as an important indicator for assessing beach stability. This paper presents a review of the progress and problems of the research on the cross-shore migration of nearshore sandbars including the bar-shape parameters, the formation theories, migration mechanisms and the methods of numerical simulation. Although considerable research on sandbar migration has been carried out by researchers both in China and abroad, there are still many problems that remain to be solved due to the complexity of dynamic processes involved, especially the coupling process between sediment transport and sandbar migration. The review highlights areas for further studies, which include differences in spatial characteristics of sandbar migration, the threshold of sandbar migration, the influence of breaking waves on near-bottom sediment transport, sandbar migration, the improvements of numerical models and the interaction mechanism between sediment transport and sandbar migration.