Abstract: Of the total water resources in the Yellow River, the contribution of surface water accounts for about 84%. However, the surface water status has undergone a significant change during the past nine decades mainly due to the combined influence of climate change and human activities. The study analyses the variability of annual runoff in the upper and middle reaches of the Yellow River. The analysis uses methods of the Mann-Kendall rank correlation test, the flow duration curve and the double mass curve. Observed stream flows for 1919—2010 at the Shanxian and Hekouzhen stations on the river are used for the analysis. Results show that there have been abrupt reductions in the observed annual runoff in both upper (at Hekouzhen) and middle reaches (between Hekouzhen and Shanxian) of the river since 1985, with a slight higher reduction in the middle reach. This is despite the fact that there have been no significant changes in precipitation over the drainage areas for the two stations during the same period of time. Apparent periodicities (low—high—low) can be observed in the variation of annual runoff in both upper and middle reaches of the river. At present, the river is experiencing it low-water period. The analysis of the double mass curve method indicates that human activities are respectively responsible for 88.1% and 84.9% reductions of annual runoff in the upper and the middle reaches of the river. Therefore, human activities appear to be the main influential factor for the change in annual runoff in both upper and middle reaches of the Yellow River.
Abstract: Daily precipitation data covering 1961—2005 from 67 meteorological stations across the upper Yangtze River basin are used to analyze spatial-temporal variability characteristics of precipitation structure in the context of climate change and human activities. The autocorrelation component in precipitation time series is eliminated by the Trend Free Pre-Whitening method, while the variability and trend in the precipitation structure are detected by the nonparametric Mann-Kendall method. Results show that over the upper Yangtze River basin and its sub-basins, the incidence rate of precipitation events for different durations decreases exponentially with the increase of precipitation durations; while, the corresponding contribution rate is found to be first increasing and then decreasing, with predominantly by short-duration precipitation events. It is detected that the year of 1976 was marked by an abrupt change for the contribution rate of short-duration (1 d and 2 d) precipitation events; while, the timing of abrupt changes for incidence rate and contribution rate of the precipitation events with long-durations of 6 and 10 days was in 1984 and in 1999 respectively. An upward trend is detected in the number of consecutive occurrences of short-duration precipitation events, with higher precipitation intensity and contributing to larger portion of total precipitation amount; while, the opposite is true for long-duration precipitation events. Tests are all significant for both above characteristics of precipitation structure amongst the Min River basin and the Dadu River basin, which are the sub-basins of the upper Yangtze River basin, as well as its main course areas.
Abstract: The Ruoergai swamp had been experiencing a rapid degradation since 1960s. However, the mechanism causing the degradation in Ruoergai swamp remains unclear, as a few studies concerning the issue can be found. The rapid degradation of swamp affects the wetland ecosystem and causes a reduction of flow rate draining into the upper Yellow River. In this study, we investigate the mechanism using the combined approach of field studies conducted in 2010—2013, and analyzing meteorological and hydrological data and remote sensing images. Results show that climate change may not be the main cause of the wetland degradation as the overall amount of annual precipitation remains steady in spite of a slow rise in temperature in the past 50 years. The analysis of remote sensing images reveals that there exists an artificial drainage system with a total length of 920 km developed for animal husbandry purposes. Water is thus drained from wetlands by the system, which causes a reduction of 648.3 km2 in Ruoergai swamp, accounting for up to 27% of the wetland degradation. Therefore, excavated artificial ditches as an intense disturbance of human activity are an important reason on rapid shrinkage of swamp. Headcut erosion of countless tributaries inside the swamp continuously draining water, lowering groundwater water level and cutting into the inside of swamp, is another important natural degradation mechanism. Connection of artificial channels and natural river networks strengthens the effect of riverbed incision and drainage.
Abstract: To improve the accuracy of land surface fluxes estimated by the Surface Energy Balance System (SEBS) under drought water stress conditions, the normalized difference water index (NDWI) as drought water stress information is integrated into SEBS to modify the value of parameter (kB-1) based on linear, exponential, and S-curve equations, which decreases with the increase in water stress. The proposed scheme is calibrated and validated by meteorological and fluxes observations in 2008—2009 from the Yingke oasis station of Heihe river basin, China. Results show that the revised SEBS model can significantly improve the land surface flux estimation in arid and semi-arid regions under drought water stress conditions. The issues of underestimation of sensible heat fluxes and overestimation of latent heat fluxes with the standard SEBS can be significantly improved by the revised SEBS. Biases in estimated sensible and latent heat fluxes are reduced by 35 W/m2 and 25 W/m2, respectively.
Abstract: Based on indoor rainfall simulation tests carried out with a soil bin, measurements are made for various physical processes including the rainfall infiltration, the surface runoff, the sediment yield, the velocity of interrill flow and the velocity of rill flow on the purple soil slop containing different rock fragment contents. The quantitative relation between rock fragment content and soil loss is thus established. Result show that soil mixed with rock fragments can have both positive and negative influences on rainfall infiltration. The infiltration capacity of soil is enhanced when the content of rock fragments less than 20%~30%, while the capacity will be reduced after the content reaching 30%. Through different action mechanisms, soil mixed with rock fragments has different influences on velocity of interrill flow and velocity of rill flow. The increase of the rock fragment content can lead to an increase in the mean velocity of interrill flow, while decreasing that of rill flow. Through altering the composition and structure of soil, soil mixed with rock fragments can improve both soil anti-erodibility and anti-scouribility. With increasing of rock fragment content, values of sediment concentration and sediment yield will be decreased significantly. The relationship between rock fragment content and soil loss ratio can be expressed by a negative and exponential function with a high degree of reliability.
Abstract: Field simulation experiments were conducted to identify the water source of the wet dune in Alxa Desert. We simulated 59 mm of precipitation, and found that the maximum infiltration depth in the dune profiles was only 46 cm, suggesting that the rainfall infiltration through sand to the groundwater is nearly impossible in this area. In the four dune profiles, δD, δ18O, and Cl- concentrations in the soil water, and the moisture contents of the wet dune at different depths, were analyzed. In Alxa Desert with strong evaporation, groundwater in the form of film water evaporates, condensates, transports to the surface, and finally discharges by evaporation. The isotopic compositions of springs, wells, lakes, and soil water show that they all originate from the groundwater, whose source is exogenous. We suggest that deep-circulation water channels may exist in Zaduo-Yabrai and the Langshan-Shigatse basement fault zone, and water leakage from the Qinghai-Tibet Plateau may be the main recharge source of the groundwater in Alxa Desert.
Abstract: This work discusses the temporal variation of various physicochemical species in the meltwater runoff of Laohugou Glacier No.12 and their correlation with dust particles in summer 2012. During melting periods, large amount of dust particles are melted from ice and snow of the glacier and dispersed into the meltwater, then transporting, which is very important for the change of physicochemical characteristics of glacier meltwater. We find that, the volume-size distribution of dust particles in the meltwater of glacier No.12 is mainly composed by three parts, which is fine aerosol particles (with diameter of 0~3.0 μm, mainly PM 2.5), atmospheric dust (with diameter of 3.0~20 μm), and local dust particles (20~100 μm), respectively. Comparison of dust particles in the snowpack and meltwater runoff indicates that, large part of dust particles in the meltwater may have originated from dust of the snow and ice, and transported into the meltwater runoff. Moreover, the temporal variation of dust and major ions (especially crustal species such as Ca2+, Na+, Mg2+, K+, and Cl-) is very similar with each other, showing great influence of dust particles to the chemical constituents of the glacier meltwater runoff. Particles concentration is relatively high in July, and decrease in August, which is well correlated with glacier melting velocity in this region. However, SO42- and NO3- concentration show an increasing trend during June to September, which may be caused by anthropogenic species input. SPM and TDS also show a similar change trend with dust particles in the meltwater, implying significant influences of glacier dust particles to TDS in the glacier region of Laohugou in Qilian Mountains in central Asia.
Abstract: Formation and development of thermokarst lakes have great influence on the cold region environment, and its lateral heat erosion can cause the embankment instability in permafrost regions. However, lake water with different physical and chemical composition has obviously different impact on cold region environment and permafrost engineering. In order to understand the chemical properties of thermokarst lakes and find out the relationship between chemical properties and their distribution along the Qinghai-Tibet Engineering Corridor, a corridor from Chumaerhe high plateau to Fenghuoshan mountain passing along the Qinghai-Tibet Highway was selected. Our study area included three sub-regions, the Chumaerhe high plateau, Hoh Xil hill region, and Beilu River basin. Nineteen thermokarst lakes along the north-south direction were observed separately for its depth, area, and shape and lake water was sampled and major cations and anions were analyzed at the State Key Laboratory of Frozen Soil Engineering, Chinese Academy of Sciences. The relationship between the physical and chemical properties of the 19 thermokarst lakes and the regional environment and thermokarst lakes distribution were studied. The results showed an obvious difference in chemical properties of the thermokarst lakes at these three sub-regions. For example, salinity of the thermokarst lakes in Chumaerhe high plateau gradually increases from north to south and the lake water belongs to saline or hypersaline water. This may be due to the lakes' spatial configuration with the big area and shallow depth, the cold and windy weather, and the high evaporation. In contrast, the salinity of lakes in Hoh Xil hill region and Beilu River basin is lower than those in Chumaerhe high plateau, and the lake water is fresh or slightly saline. The lakes at these two sub-regions are deep and the terrain is hills or basin, which reduces their evaporation. The study provided guidance for the disease control of permafrost embankment and the future engineering planning and design along this corridor.
Abstract: In this study, we develop an integrated model of hydrodynamic-sediment-heavy metal transport, which includes physical and chemical dynamics during the process of heavy metal adsorption in sediments. For this model, the traditional surface complexation model is modified to include sediment surface discharge, and then applied to represent the chemical bonding activities between heavy metals and sediment surface groups. In addition, according to the conditions of chemical reactions, two layers (aerobic layer and anaerobic layer) are included to considering topography evolution. The model is finally calibrated by simulating the transport of Ni, a trace metal, in a flume experiment. A comparison between observed data and the simulated results indicates that the integrated model is rational and can properly describe the complex process of heavy metal transport in sediments.
Abstract: The two-dimensional river ice dynamic model DynaRICE is used to study the optimal design of ice deflection booms in a channel bend with an intake diversion channel. The coupled hydrodynamic and ice dynamic equations are solved by the finite element method and smooth particle hydrodynamics method, respectively. The flow characteristics and the ice movement and accumulation patterns in the channel, as well as the force on ice deflection booms are examined. The result shows that the surface ice moves along the outer bank of the bend and accumulates at downstream of the intake. The effect of the transverse circulation on surface ice movement can be neglected. Ice deflection booms with an appropriate angle and length upstream of the intake can prevent ice from entering the diversion channel. However, ice can still accumulate at downstream of the intake and extend into the intake. A downstream ice boom is needed to prevent this from happening. This study provides a method for the design of ice booms to prevent the ice accumulation problem in river bend intakes.
Abstract: Numerical simulation of a vertical round jet in wave-current environment was performed using the Large Eddy Simulation (LES) method. The zero-gradient condition combined with a sponger layer was imposed at the outflow boundary to reduce the numerical reflection. The linear and non-linear superposition of wave and current boundary conditions were adopted at the inflow boundary respectively. The latter was proved to be of higher precision by comparison of the velocity profiles with the experimental data. Numerical results show that under the combined effect of wave and current, an apparent "water masses" phenomenon appears on the upper part of jet body and the jet velocity vectors are deflected closer to the bottom than that in a pure current environment, which is consistent with the previous experimental observations.
Abstract: In view of the gradual riverbank collapse, a hydrodynamic model for assessing riverbank stability is established on the base of soil mechanics and river dynamics theory. Combined with generalized model tests and numerical calculation, the mechanism of riverbank stability is analyzed, and the failure reason for slight slopes is explained. Results show that the slope should be stable when the seepage exit gradient on the slope surface is less than the critical gradient of infiltration failure. After the toe of the slope was washed away by current, partial infiltration failures on the slope begin to appear and will develop with the increase of the seepage exit gradient due to the shortening in seepage path length. The back soil mass will fail successively due to lack of support. The gradual soil mass failure will develop backward with time leading to the collapse and destruction of the entire slope eventually.
Abstract: Sediment transport induced by wave breaking on the sandy sloping seabed leads to bed profile changes. Research on the mechanism of sandy seabed morphology change under the action of breaking waves is of great important to analyze the beach evolution. Experiments in this study are carried out in a wave flume on a 1:20 sloping artificial seabed, which is made of sands with median diameter of 0.47mm. The bed profile variations and the suspended sediment concentration on the top of the sandy bar are measured. By calculating the sediment transport rate in the surf zone as well as the dimensions and moving speed of the sandbar, the evolution of the seabed profile under breaking waves is analyzed. Experimental results show that the suspended sediment concentration in the surf zone on top of the sandbar is closely related to the local water depth and bed morphology. The concentration of the suspended sediment is larger when the sandbar forms and moves horizontally. There are both onshore and offshore movement of the sandbar and the back-and-forth movement of the sandbar on the slope have a random period. The dimensions of the sandbar tend to be stable and the net sediment transport tends to be zero under the action of wave trains. The result provides a reference for further study on the beach evolution.
Abstract: Low Impact Development type's Best Management Practices (LID-BMPs) have been regarded as cost-effective measures for mitigating urban runoff impacts. However, as the implementations of LID-BMPs are interacted with many factors, the research on LID-BMPs planning is still lag behind expectations. Based on the survey of LID-BMPs research and practices, a novel method for LID-BMPs planning is proposed to meet the needs of LID-BMPs implementations to China. A college campus in the Foshan city of China is chosen as a case study site to test the proposed method. Four planning scenarios for the college development are proposed, which are the natural condition before development, the existing campus development plan without LID BMPs, a least-cost LID BMPs implementation scenario (i.e., scenario 1) and a maximized LID BMPs performance scenario (i.e., scenario 2). System for Urban Stormwater Treatment and Analysis Integration (SUSTAIN) is a decision-support GIS tool developed by the U.S. Environmental Protection Agency for strategically placing BMPs in urban watersheds. SUSTAIN is used in this study to support the scenario optimization. The scenarios analysis emphasizes on the effects of runoff quantity (runoff volume and peak flow) and quality (SS, COD, TN, TP) controls. The scenario optimization uses the reduction rate of annual runoff volume as the objective. Scenario 1 and scenario 2 are further optimized by SUSTAIN, and the best cost-effective scenario is obtained.
Abstract: In order to quantify the water utilization in grain production from different perspectives, an analysis is performed on multiple water productivity indexes including the gross inflow water productivity (Pwg), the irrigation water productivity (PwI), the evapotranspiration water productivity (PwET) and the generalized water productivity (Pwu). The spatiotemporal variation of the four productivity indexes and the correlations among them for irrigated land in China are examined. Results show that the national values of the four indexes being 0.694, 1.361, 1.314, and 0.860 kg/m3, respectively. Moreover, these water productivity indices had increased between 1998 and 2010 in almost all of the provinces studied, although their spatial distributions remained similar in 1998, 2005, and 2010. The highest and lowest values are found for the provinces in and around Huang-Huai-Hai Plain and for the provinces in northeastern China, northwestern China, and south of the Yangtze River, respectively. The degree of spatial difference decrease as follows: PwI >PwET >Pwu > Pwg. We have found significant linear correlations between each pair of indexes, with correlation coefficients greater than 0.950 between Pwu and all other indexes. Despite considerable differences between the four indexes in terms of their applicability and numerical performance, all of them can be used to measure differences in the water productivity of grain crops between provinces.
Abstract: This study takes the Luoshan drainage area in Four-lake Watershed in Hubei Province as an example. The drainage modulus is calculated with an empirical formula. The effects of water surface ratio, proportion of paddy field to dry land area, urbanization, irrigation mode and underlying surface changes on the drainage modulus are analyzed. Results show that the drainage modulus decreases with an increase in the proportion of paddy field to dry land area, and decreases with an increase in the water surface ratio, as well as increases with an increase in ground hardening rate. In addition, the effects of water surface ratio on the drainage modulus are greater than those of the proportion of paddy field to dry land area, and the ground hardening rate. The drainage modulus is smaller with intermittent irrigation than that with traditional irrigation. Based on the water logging control standard of a three day rainstorm with a 10 year return period, the drainage modulus had increased from 0.38 m3/(s·km2) in 1994 to 0.46 m3/(s·km2) in 2011 because of underlying surface changes. In 2011, the drainage modulus met approximately the water logging control standard for a three day rainstorm with a 19 year return period, based on the underlying surfaces in 1994.
Abstract: To explore the possibility of using the Continuous Stress-Day Index (CSDI) of waterlogging and excessive soil water as a drainage standard for rice paddy fields, consecutive and dynamic experiments on waterlogging and excessive soil water are conducted in testing pits during the heading and flowering stage of paddies. An CSDI model is developed to deal with waterlogging and excessive soil water issues. The model solution and the weight coefficient of waterlogging (CW) are provided. The relationship of rice yield and CSDI is established through the analysis of experimental data. Results show that the stress and continuous stress from surface and subsurface waterlogging can reduce the rice yield in various degrees. The degree of yield-reduction is relatively high due to the continuous stress from surface and subsurface waterlogging. The weight coefficient CW is a state variable that varies with the status of surface and subsurface waterlogging. A linear relationship between relative rice yield and CSDI can be observed under the condition of continuous stress from surface and subsurface waterlogging. Thus, the index CSDI can be utilized as a drainage standard for paddy fields, and the controlled drainage rules could be developed using the CSDI model.
Abstract: Nowadays, engineering hydrology is facing many challenges such as the extrapolation or regionalization of the observations of watershed behaviors. The difficulties in producing concise, easily understood explanations of watershed behaviors have been considered as a theoretical bottleneck by the Prediction in Ungaged Basins (PUB) of the International Association of Hydrological Sciences (IAHS). An applicable solution is to develop a classification system based on dimensionless similarity indices, group watersheds into distinct groups, and then transfer observed results from gauged to ungaged basins under the frame of hydrologic similarity. In this study, it is found that hydrology does not have a theoretical system of classification and similarity as hydraulics, chemistry and biology, etc. By reviewing and comparing the similarity theory in other disciplines, we discussed the concept of hydrologic similarity, its basic methodology and three primary components, i.e., driving, structural, and hydrodynamic factors. Finally, two useful methods for hydrologic similarity (mathematical and dimensional analysis) as well as the future directions are discussed.
Abstract: As the key content and core element identified in the practice of drought disaster risk management, it has become a hot-button issue on how to properly assess the drought disaster risk in the field of both science and technology. Starting with reviewing the definition of drought disaster risk concept in the scientific community, the differences between the concepts of the drought risk and the drought disaster risk are made clear in this study. The mechanism of drought disaster risk formation is then investigated and elaborated. A quantitative framework for assessing drought disaster risk is first proposed, this is achieved by establishing the quantitative relationship among three important parameters: the drought frequency, the potential loss and the drought resistance capacity. The key techniques used in the framework are highlighted and discussed, which include the drought frequency analysis, the drought disaster loss assessment, the drought resistance capacity assessment, and the drought disaster risk characterization. The active issues and difficulties related to the techniques are also respectively addressed.