Abstract: The monthly GRACE-based terrestrial water storage (TWS) data in upper and middle Yangtze River basin during 2002—2013 are compared with measured precipitation and discharge, and model simulated soil moisture from the aspects of temporal trend, correlation, and time lag. Four drought indices, including Standardized Water Storage Index (SWSI), Standardized Precipitation Index (SPI), Standardized Runoff Index (SRI) and Standardized Soil Moisture Index (SSMI), are used to assess the intensity and timing of drought events in the upper and middle Yangtze River basin. The results show that: TWS exhibits similar temporal variation as precipitation, discharge and soil moisture in the upper Yangtze River basin, exhibiting no significant trends, whereas TWS has the same significant upward trend as annual reservoir water storage in the middle Yangtze River basin, indicating significant impacts of human activities on TWS in the middle Yangtze River basin; the number of months with drought at various levels indicated by different drought indicators are close to each other, although not equal; the GRACE-based SWSI has poor capability to capture extreme droughts; the comparison of the timing of drought events indicated by different drought indicators shows lags between meteorological drought and hydrological drought and agricultural drought.
Abstract: Based on those observing series of annual water and sediment volumes from 1950 to 2010, a nonlinear response model was built statistically at the Toudaoguai gauging station in the Upper Yellow River in this paper. And the contribution rate of those leading driving factors in the model were estimated quantitatively. The results showed that: From 1950 to 2010, the annual mean runoff reduction is 0.223 billion m3/a, the annual mean sediment reduction is 2.7 million t/a. Especially from 1987 to 2010, the decreasing trends of annual runoff and sediment are more obvious, and the sediment reduction is greater than runoff reduction significantly. From 1969 to 2010, the contribution rate of climatic factors and underlying surface factors for annual runoff and sediment reducing modulus at the Toudaoguai gauging station is 2:8 approximately, underlying surface factors occupied a dominant position. Among them the water diversion in the Ningmeng Irrigation Area is the largest driving factor on the runoff reduction at the Toudaoguai gauging station, whose contribution rate reached 42％. The reservoir operation of Longyangxia and Liujiaxia reservoirs is the largest driving factor on the sediment reduction, whose contribution rate reached 34％. It can be predictable that in the future, the variation of runoff in the main channel of upper reach of Lanzhou, and sediment volume from those tributaries between Lanzhou and Toudaoguai will be the two natural driving factors for the annual water and sediment variations at the Toudaoguai gauging station in the Yellow River. Therefore the water diversion from the main channel for irrigating and integrated management of soil and water conservation in those tributaries will be key methods for controlling the variations of water and sediment.
Abstract: In order to analyze the relationship between deep layer moisture infiltration and rainfall in mobile dunes, using YWB-01 deep layer moisture infiltration recorder and soil water dynamics theory, this study explains the rainfall infiltration moisture transfer process in Mu Us Sandy Land mobile dunes, as well as the infiltration recharge characteristics at the soil layer of 150cm deep. The results showed that: the major source of deep layer soil moisture in mobile dunes was rainfall infiltration. The infiltration recharge amount was 141.4 mm for 2010 and 355.8 mm for 2011, counting for 55.1% and 68.2% of the total rainfall amount of that year. The major recharging season of deep layer infiltration lasted from May to November, and the recharge amount during these months counted for 95% of the total annual amount. When the soil moisture condition remained within the field moisture capacity, rainfall's recharging effect on 150 cm deep soil layer was mainly influenced by rainfall amount and density, with a significant positive correlation (P<0.01) between infiltration and rainfall amount. Water usually infiltrated into the 150 cm deep soil layer at 30 to 48 hours after the start of rainfall. The infiltration recharging rate increased rapidly in the first 3 to 5 hours, reaching its maximum at 3 to 8 hours, before decreasing slowly afterwards. The entire infiltration recharging process could last for longer than 96 hours.
Abstract: Rain gardens can be used effectively for retaining stormwater runoff and mitigating the negative impact of urban development on the aquatic environment. By monitoring the inflow and outflow processes of a rain garden over four years in Xi'an, China, this paper presents a study on the effect of a rain garden on storm runoff reduction; the sustainability of the rain garden operation was examined on the basis of soil sampling for particle size analysis and onsite measurements of infiltration capacity. The results showed that, for the experimental rain garden constructed with ponding depth of 15 cm and flow catchment area ratio of 20:1, only 4 storm events produced overflow from the rain garden out of the 28 monitored events, and the overflow volumes were generally small; there were no overflow occurred in two years, all inflow infiltrated in the rain garden; there was maximum 3 overflow events in one year, but the runoff reduction rate was as high as 96.8％; the storms that caused the rain garden overflow were all high intensity and short duration events. The onsite infiltration measurements showed no significant change in the infiltration capacity over the four years, the rain garden infiltration capacity was maintained at 2.400 m/d. The soil particle size analysis showed that, sand content at the surface layer of the rain garden increased from 7.36％ to 20.55％, while the silt and clay contents decreased accordingly. These results indicate that rain gardens can reduce storm runoff significantly, and the stable infiltration capacity entitles them a promising future in the study area. Findings from this research may provide theoretical basis and technical support for the sponge city construction in China.
Abstract: Water level and flow velocity are two critical factors for flood control and forecasting. However, to our knowledge, there are few universal models that have been able to simulate water level and flow velocity effectively especially in the river channels without observed discharge data or stable stage-discharge relationship. In this study, the derivative expression of the friction is proposed using dimensional analysis based on water balance equation and force equilibrium equation. Then, the bi-variable (water level and flow velocity) coupling model is established by solving the derived differential equation. The developed model is tested in four river reaches in the Qiantang River, the Ganjiang River, and the Guijiang River. Our results indicate that the model can provide good simulations of water level in the study area (with coefficient of determination larger than 0.7 during both calibration and validation processes). This study also confirm the rationality of the model structure and its effectiveness in simulating the river flow.
Abstract: Theory analysis and numerical simulation combination method were employed for simplifying numerical calculation process of two-dimensional cumulative infiltration under furrow irrigation. By analyzing the impacting factors of initial water content, water depth, bottom width, slope parameter, soil texture and bulk density effects on edge effect and fitting parameter γ, a relationship between fitting parameter γ and the main influence factors was built and a simplified method for cumulative infiltration of furrow irrigation was proposed. The results show that the initial water content, bottom width and slope parameter have slight influences on the edge effect, however, water depth, soil texture and bulk density have greatly influence on it. Being closely related with water depth, fitting parameter γ decreases with the increase of water depth, but is less sensitive to the initial water content, bottom width, slope parameter, soil texture and bulk density, therefore those impacting factors can be ignored. Based on the references, the reliability of the proposed method in this paper is verified. The results show that the calculated values of the cumulative infiltration agree well with the measured values and simulated values by the HYDRUS. Therefore, it is reliable to estimate the cumulative two-dimensional infiltration with the proposed method under furrow irrigation.
Abstract: In order to figure out the quantitative influence on wash-scour erosion at the bottom of high and steep slope of engineered landform caused by upslope runoff, the typical abrupt slope (36°) of engineering deposits along the expressway from Shenmu to Fugu was selected in the research to conduct a set of field runoff scouring experiments. Given that total runoff amount was kept constant, four types of upslope runoff were designed to conduct the subsequent analysis of the downslope runoff erosion response and sediment transport process on the abandoned spoil-deposit. The results indicated that: ① The type of upslope runoff had little influence on total surface runoff production at the bottom of the deposit slope, but it interfered the process of slope erosion and sediment yield, which increased the amount of soil loss; ② All the indicators of runoff depth, unit runoff erosivity, and stream power can well predict the intra-event sediment delivery modulus at the bottom of deposits slope induced by individual variable upslope runoff events; ③ The unit runoff erosivity based on flow discharge per unit width and runoff depth, can be used as the index to represent the change of runoff erosion power in single upslope runoff events, regardless of the type of upslope runoff. The results can be helpful in evaluating the intensity and degree of soil erosion, establishing erosion model in dramatically disturbed areas, and preventing from newly-arising water and soil losses against engineered landforms.
Abstract: The stability of mountain stream bed is directly related to the effects of artificial step-pool system on mitigation of riverbed incision and control of debris flow. In this paper four cases of artificial step-pool system constructed in 2006—2010 are analyzed to figure out the control effect and the causes of destruction of the system. The step-forming boulder is analyzed as an individual object and forces on the boulder is derived. A new model of step-pool stability is obtained, which can be used to analyze the impact of the incoming discharge and scour angle. The step stability primarily relies on the size of step-forming boulders, bed slope, flow discharge, and scour angle. The peak discharge in flood season and scour of downstream step are the fundamental causes of step failures. The stability of artificial step-pool system during flood peak is the key for long term use of the system.
Abstract: Large-scale flood flows discharged from high-dam reservoirs are extremely difficult to measure due to the presence of fast developing, highly fluctuating flow surfaces. This study presents a novel in-situ method suitable to monitor surface topography as well as velocity fields of such complex flows. The new method combines stereo photogrammetry and large-scale particle image velocimetry (PIV). The two-camera stereo photogrammetry adopts the SIFT approach for spotting and matching distinct points, and to enhance measurement accuracy and efficiency the internal and external camera parameters are calibrated separately. The large-scale PIV system traces texture of the surface flow through image acquisition, grey standardization, background removing, and median filtering. Real surface velocity field is constructed from velocity field and surface topography measured by two cameras simultaneously. Application of the new method to Xiangjiaba project has been successful.
Abstract: In order to study the distribution law of Shields curve in laminar regime, the critical tractive force for the onset motion of uniform non-cohesive glass beads is investigated based on the CCD (charge coupled device) imaging technology combined with laser scanning and computer image processing technology, using a mixture of water and glycerol. According to the laminar flow theory, the rolling model for the onset motion of non-cohesive particles is established and an equation for non-dimensional critical tractive force is derived. Experiments show that the particle Reynolds number versus Shields number is a systematic band distribution in the laminar region; further, fluid flow induces bed armoring and leads to the decrease in particle protrusion on the granular surface, the critical tractive force can be doubled consequently. This indicates that the structure of the granular surface has a significant impact on the critical tractive force for the onset motion of particles, and band distribution is a characteristic of Shields curve in the laminar regime.
Abstract: It has been proved that analysis of the two-dimensional pollutant concentration distribution characteristics during the expansion of contaminated zone in river-offshore discharge, and prediction of the concentration on the environmental sensitive sites have aroused a considerable attention of the academic and engineering communities. Its boundary reflection being taken into consideration based on the analytical solution of the simplified two-dimensional advection-diffusion equation for rivers, the formula of x1.2'threshold, which categorizes the wide-and medium-wide rivers based on the relative offshore distance a' (defined as the ratio between the distance from the discharge outfall a and river width B), has been proposed through series computational experiments on off-shore discharge, concentration distribution contouring, and mathematical induction and analysis. The definition of maximum concentration axis in river cross-sections has been proposed, along with its piecewise equations applying to each sub-situation classified by certain criterion. The thresholds xe' and xk' separating the x-axis segment, curved segment and near-shore segment of the defined maximum concentration axis are given with a simplified calculation formula for cross-section maximum relative concentration, relative concentration along the centerline and banks of the rivers for each segment. The results afford a theoretical basis for the prediction and assessment of the river water environmental impact.
Abstract: Based on the measured data and information about tidal current velocity, suspended sediment concentration (SSC), and surface sediments in the Laizhou Bay, the effects of tidal current, residual current, tidal bottom stress, and bottom sediment type on SSC variation were analyzed. The mechanism of suspended sediment transport is also addressed by using material flux analysis. The results show that: ① The sea area of study was controlled by semidiurnal tides and characterized by rectilinear current and the SSC exhibited cyclic tidal change, with the near-bottom SSC being significantly correlated with tidal current velocity and with tidal bottom stress during the flood and ebb stages, which indicates strong re-suspension; ② The type of bottom sediment is closely related with SSC value, and fine-grained material is more prone to suspension; and ③ Slack water transport and tidal pumping effects are the main dynamic factors contributing to suspended sediment transport in the Laizhou Bay area.
Abstract: In the vast northern regions, ice jam can be easily formed during winter times, which can further result in ice jam flooding. Due to the presence of bridge infrastructures, the flow field can also be complicated. To study the impact of bridge pier on ice jam, the present study was conducted. By using experimental approach, the mechanism of backwater height variation was measured. It shows that the presence of bridge pier significantly changes the backwater height during ice jam. The ice jam evolution can be classified as "before pier" and "after pier" conditions. Erosion on ice jam around bridge piers can also be noted, which further complicate the ice jam stage development. It is also found that with or without bridge pier, the mechanism of backwater height shows similar trend under different flow conditions and ice discharge. However, with a larger diameter, the backwater height variation is larger under the same flow and ice conditions. With the same blockage ratio, double piers can results in a higher backwater height increase comparing to a single pier.
Abstract: Joint operation of multiple water sources plays a significant role in alleviating the conflict between urban water supply and demand. Firstly, to achieve the effective distribution of various urban water sources, an optimization model based on the network topology of "Source—Plant—User" urban water supply system is proposed. The objectives of this model include social benefit and total water supply cost, subject to the capacity of water sources, water pipes and water plants, and the water demand of users. Secondly, NSGA-II algorithm is applied to solve the model, based on which the optimal condition for the equilibrium solution is obtained. Thirdly, as a case study, the water-supply system in Tianjin city is a complex multi-source water-supply system after the Mid-route of South-to-North Water Diversion Project (SNWDP) begins to divert water to Tianjin. The optimization results show that this model could successfully provide corresponding reasonable allocation solutions compromising social benefit and water supply cost under different wetness and dryness probabilities at water sources. And the causes of water shortage and the existing design deficiency in the urban water supply network could be reflected through result analysis. For example, the water supply capacity (1 473 million m3) of the worst condition could satisfy the water demand of Tianjin (1 377 million m3); whereas, the water shortage of recommended solution, which balances the social benefits and water shortage, is 244 million m3 with water supply cost of 3 260 million yuan due to the capacity restriction of the pipelines under the specific water supply rule. Above all, this model is feasible to a certain extent and provides technical support for ensuring urban water-supply security of Tianjin city.
Abstract: Within the cryosphere, glacier-fed streams exhibit distinctive thermal regimes due to glacier melt influences; accordingly, these streams host a unique coldwater ecosystem. The role of water temperature as a driver of various intra-ecosystem processes is particularly significant in glacierized basins due to the strong coupling and high sensitivity between atmospheric and in-stream processes. In this paper, we review studies of the temperature characteristics in glacier-fed river streams, the influencing factors, and the response in aquatic ecosystems. Previous analyses have shown that glacial rivers are characterized by low temperatures and remarkable spatiotemporal temperature variations. Influencing factors in glacial rivers can be summarized in four major categories: heat transfer at the air-water interface, heat transfer at the water-channel interface, runoff components, and climate change and human activity. The response of a glacial river thermal regime to its physicochemical properties results in changes to the river water quality and thermo-hydrological fluxes. While the response of the aquatic ecosystem changes the distribution and structure of aquatic system with changing glacial stream temperature, once a certain threshold is exceeded, the change will be irreversible.
Abstract: This study comprehensively concluded the water right allocation course of the Colorado River in America and America—Mexico to seize and learn the century-long water right law and the situation of the Colorado River. Each water law focuses remarks on the background, purpose, content, and their relationships. The water right allocation course of the Colorado River demonstrates that the persistence of the water right is assured by the cooperative development of both engineering and non-engineering measures. Meanwhile, natural resources, regional socio-economic development, ecology, and international environment should also be considered. Under the water right treaty framework, flexible market mechanisms can improve water resource efficiency, which is an effective manner in addressing changes in the demand and supply of water resources. The water right allocation of the Colorado River has an important reference value for China in both claiming transboundary river water right and optimizing local water resource management.