Abstract: Based on the positioning observation of precipitation in the hinterland of the Badain Jaran desert and data from four surrounding gauges in the vicinity of the desert, the characteristic of precipitation in the hinterland of the desert is examined.The effect of megadunes on precipitation is primitively analyzed.The difference in precipitation amounts between the margin area and the hinterland of the desert is discussed.Results show that light rain dominates the hinterland and the most common rainfall events are likely to be short in duration less than two hours.Precipitation exhibits a great deal of seasonal variability, and the annual precipitation depends very much on a few rainy days.A good consistency is found in the seasonal distribution of precipitation between the hinterland and the margin area.During the observation, the precipitation amount of the hinterland is lower than that of the southern margin, but is evidently higher than that of the northern, northwestern and southeastern margins.It is possible for the hinterland region to encountering local heavy rainfall events with precipitation greater than 20 mm and the maximum intensity of precipitation exceeding 4 mm/h; however, the occurrence of such events is rather instantaneous and random.It is evident that a megadune can influence precipitation as the annual precipitation and rainy days on the top of the megadune are slightly more than those in the interdune areas, and so do the duration and accumulation of a single precipitation event.During heavy rainfall events, spottiness is likely to occur on an average scale of 16.8 km.The cross-correlation analysis demonstrates that the space correlation decreases significantly with the increase of distances in the summer time of a year.However, the space correlation to 50 km is still high in the winter time of a year due to cold frontal precipitation.
Abstract: Chute cutoff is one form of natural cutoffs on meandering rivers.This paper studies the patterns and development processes of chute cutoffs through field investigations and statistical analyses using remote sensing images.The natural chute cutoffs are divided into shoal-cutting pattern, ditch-scouring pattern and embayment-eroding pattern.The shoal-cutting pattern is caused by the direction of main flow turning to the shoal of convex bank during flood, which results in overbank flow on the shoal and a new chute on shoal.Such a cutoff is found on 67 meanders among the examined rivers.The average ratio of the bend curvature radius is about 3 times of the average stream width and the average angle of dividing flow is about 55. The ditch-scouring pattern is the result of pre-flood overflows forming several ditches, and one of the ditches is scoured, enlarged and deepened, and finally formed the cutoff.In the embayment-eroding pattern, the mainstream flow erodes the inside bank of river bends and forms an embayment, and then the flood erosion results in the downstream extension of the embayment until cutoff the meander.
Abstract: Equifinality is a difficult but unavoidable challenge in hydrologic modeling.A framework is established and presented to estimate the three baseflow parameters in the Variable Infiltration Capacity (VIC) model using soil properties.The new parameter estimation method is tested for streamflow simulations on three distinct catchments in hydro-climatic conditions in China.The simulations are compared to the previous calibrated results.The new method can reduce the number of VIC calibration parameters from six to three, thus decreasing model equifinality and uncertainty.The sensitivity of the calibrated parameters under the new framework is improved as demonstrated by the Monte Carlo simulations.The parameter uncertainty can also be reduced.In addition, the uncertainty of VIC simulations is assessed using the Generalised Likelihood Uncertainty Estimation (GLUE) method.Results show that the uncertainty of streamflow simulations (or, confidence interval) is low with the new parameter estimation method compared to the uncertainty resulted from the previous calibration method.The new method is applicable to the VIC model and other similar hydrologic models for streamflow simulations.
Abstract: Based on ArcGIS spatial analysis tools and four wetland remote sensing images from 1978, 1990, 2000 and 2008, the Nenjiang River basin can divided into 43 subbasins using the Soil and Water Assessment Tool (SWAT) model.A contrastive analysis is performed on marsh wetlands to investigate the differences between information on rainfall and runoff and wetland degradation provided by remote sensing images.Further analysis is done on the subbasins with serious issues on wetland loss and degradation.On the other hand, two land-use maps are used to generate the land-use transition matrix of the Nenjiang River basin.The result shows that the marsh wetlands in the f Nenjiang River basin have degraded seriously during the period 1978—2008, especially between 1990 and 2000.This can be closely related to the changes in precipitation and runoff, as well as the influence of human activities such as the conversion of land-use changes and water conservancy constructions.Furthermore, the variation of marsh areas and the basin runoff coefficient exhibit a significant positive correlation at the level of 0.01, and the Pearson correlation is 0.90. Under the influences of climate changes and human activities on the hydrological processes and water resources, the wetland areas have gradually been shrinking over the years, causing a negative impact on the balance of the wetland ecosystem in the Nenjiang River basin.
Abstract: A new method to evaluate the risk of water resources under climate change is proposed.The method is mainly comprised of three steps: ① build a dynamic model representing the water resources system; ② do stochastic analysis and then build a climate response function which allows linking the climate states to the performance indicator of the water resources system; ③ the climate information of GCMs is tailed to evaluate the risk.Finally, this method is applied to evaluate the climate change induced risk in Quabbin Reservoir, Massachusetts, United of States.Through 36 GCMs in A2 scenario within two periods 2036—2065 and 2066—2095, the results show that the risk with 100%-140% historical net basin supply (NBS) annual standard deviation is between 0.25 and 0.30 in 2036—2065, and between 0.30 and 0.45 in 2066—2095.
Abstract: The Mcmahons Creek catchment is located in southeast Australia, where a bushfire occurred in February 1983.The catchment is selected for a case study to investigate the bushfire impacts on the streamflow regime.The Australian Water Resources Assessment System Landscape (AWRA-L) model and the Chinese Xin'anjiang model are used for hydrological simulations on the catchment.The impact of bushfire on the streamflow regime can be measured by the difference in runoff before and after the occurrence of the bushfire.The result shows that the average of annual runoff in the first 14 years (1983—1997) after the bushfire is increased by 140 mm for the AWRA-L model, and 123 mm for the Xin'anjiang model.The corresponding increases are 33% and 29%, respectively.This is compared to that before the bushfire averaging for the period 1974—1982.During the period 1998—2004 (or the second 14 years after the bushfire), another increase of 43 mm (10%) is obtained for the AWRA-L model.While for the Xin'anjiang model, the extra amount in annual runoff is 33 mm (8%).The study demonstrates that although there is a substantial increase in annual runoff in the immediate post-fire period, the increment of runoff generation will be gradually reduced due to the recovering of plantations.Logging is an important factor for the runoff increase in the first 14 years after the bushfire.The study also provides a reference to the practice of water resources management in forest catchments.
Abstract: A two-dimensional numerical model is presented, which employs a finite volume method based on an unstructured triangular mesh, and uses the Roe-MUSCL scheme and the predictor-corrector procedure for time stepping.In the model, the source terms for the transport of cohesive and non-cohesive sediments are respectively calculated by different methods.Besides, the formulae of incipient velocity and erosion source term for cohesive sediments are both applied.The model is first validated against the available observed data obtained from a flume experiment.It is then applied to simulate the processes of hydrodynamic and sediment transport in the Haihe Estuary.The model predictions generally agreed with the observed data measured during the neap and spring tidal cycles in September 1995, which demonstrates the capability of the model to simulating the transport process of both cohesive and non-cohesive sediment in muddy estuaries. The use of different sediment transport treatments on model simulations is further investigated.The result shows that it is necessary to consider the transport of both cohesive and non-cohesive sediments in muddy estuaries.
Abstract: The flow and sediment regimes downstream of Three Gorges Reservoir have undergone a significant change since the beginning of its impoundment in June 2003.Accordingly, the spatial variations in downstream channel morphology will be adjusted, in particular in the Jingjiang reach of the middle Yangtze River with eroded bank materials.In this study, the lateral migrations of channels in the Jingjiang reach in response to changes in flow and sediment regimes are investigated.The turbulent flow and sediment transport as well as the bank erosion process are simulated by two- and three dimensional numerical models.No significant changes can be found in the overall evolution of channel planform in the Shishou segment in the lower Jingjiang reach.However, localized bank collapses and plane deformations are likely to intensify due to the reduction of sediment transport, especially on the apex of bend.For the Shashi-Xinchang segment in the upper Jingjiang reach, the overall evolution of channel planform is reduced compared to that before reservoir impoundment.Up to 50% reduction can be expected in some local segments.
Abstract: Taking the accretional mudflats on the Jiangsu central coast as an example, a process-based morphodynamic numerical model is built.Mechanisms for the evolution of double-convex cross-shore profile are studied for the dominant long-shore tidal current and sufficient supplies of abundant sediments.The result shows that the flow velocity decreases sharply from the subtidal flats to the low waterline, and then decreases slowly landwards.The abrupt change in flow regime brings a high sedimentation rate along the low waterline, and forms the upper convex point in the area.During neap tides, the sedimentation rate will be greater than the erosion rate during spring tides over the middle subtidal flats, inducing a higher siltation rate.Furthermore, weak ebb current over the middle intertidal flats is unable to transport sufficient upwind sediment seawards, which induces a lower sediment concentration and a lower siltation rate over the upper subtidal flats during the final stage of ebb tides.Eventually, a low convex point will be formed over the middle subtidal flats.With the accretion of tidal flats, the levels of the upper and lower convex points will have a shift trend to high water level and low water level, respectively.Our results may not be in good agreement with other studies.More field observations are needed to support further researches.
Abstract: Aimed at addressing the problem of overexploitation of water resources, the current study focuses on the issues concerning economic accounting for water resources and its depletion and environmental degradation.The reasonable threshold value can thus be determined for water resources development and utilization.Based on the UN System of Integrated Environmental and Economic Accounting (SEEA) tool, an evaluation model is developed to estimate the water environment adjusted net domestic product (WEDP) after consideration of the consequences of water resources depletion and degradation.The pros and cons of water resources depletion and degradation are considered in the model development.The maximization of WEDP is set for the objective of water consumption, and is used as the reasonable threshold value for water resources development and utilization.For the Haihe River basin, the current and 2020 threshold values should be 29.2 billion m3 and 28.7 billion m3, respectively.However, the status quo on water resources development and utilization has already exceeded these reasonable threshold values, causing eco-environment damages across the basin.
Abstract: Focusing onthe problems of continually declining shallow groundwater levels on the Hufu plain of North China, the variations and response mechanisms of groundwater levels, grain and vegetable planting intensity, effective irrigated areas and precipitation are studied.A large amount of observational data collected in the past 50 years is analyzed using statistical methods and the MapGIS technology.Results show that before 1980s, the magnitude of decline in groundwater levels is small in response to the increase in the grain and vegetable planting intensity.The decline would be 0.36 m and 0.43 m, respectively; should the planting intensity and the sown area of summer grain crops and vegetables increase 0.01 and 10000 hm2, respectively.However, a significant decline in groundwater levels has been observed since 1980s.The decline would be 0.69 m and 1.15 m, respectively, with the same changes in both planting intensity and sown area of summer grain crops and vegetables.Such a decline is not only the result of the increase in the grain and vegetable planting intensity, but the result of the decrease in annual precipitation on the plain.Should there be a reduction of 100 mm in annual precipitation; the groundwater exploitation for agricultural irrigation would be increased by 35.7 mm.
Abstract: A combined approach of evaporation experiment and mathematical modeling is used to analyze the influence of osmotic potential on the bare soil evaporation rate.The result shows that the osmotic potential is proven to be the main reason for the decline of evaporation rates in saline soils when no salt precipitation occurs.The rate decline is almost linearly proportional to the decrease in osmotic potential, and is also affected by air temperature, air relative humidity, soil temperature, and soil matrix potential.When a constant water flux is supplied to the topsoil, the evaporation rate would always tend to be the constant value.However, the evaporation rate in saline soils is rather slower if the saline water is supplied to the topsoil, and the steady evaporation rate would tend to be a bit slower than the water supply rate.
Abstract: A numerical model of the Northwest Pacific is developed to study tidal system and tidal level changes due to mean-sea-level rise in marginal seas near China. The results show that after mean-sea-level rise, phase lags are increased to the east and decreased to the west of amphidromic point. The amplitude is enhanced to the north and diminished to the south of amphidromic point. Due to mean-sea-level rises, the mean tidal range is enlarged in the Liaodong Bay, the upper reaches of Bohai Bay, seas east of Liaodong Peninsula, coast of Haizhou Bay to the south of Shandong province, the north coast of Jiangsu province, the Taiwan Strait to the east of Zhejiang province, and the South China Sea. The maximum range is 0.40 m after mean-sea-level rise 0.90m. The mean tidal range is reduced in estuary of Yangtze River, Hangzhou Bay to Tsushima Strait, the west coast of Korea, and Laizhou Bay. With the increase of sea level rise, tidal range varies with relatively stable rate in the Bohai Sea, Taiwan Strait, and it with fluctuation in the Yellow Sea, East China Sea and South China Sea. Variation of mean high water level is in accord with tidal range. It uplifts more over than the mean-sea-level in areas where tidal range raises. That means the risk would increase of coastal areas to protect storm surge and other marine disasters.
Abstract: A series of channel experiments were carried out to investigate salt intrusion lengths with different tide ranges. The experiments show that there is a critical tide range value, with which the salt intrusion length reaches its minimum. Tide range increasing results in rapidly decreasing salt intrusion length if tide range is smaller than the critical value, while salt intrusion length slowly increases with increasing tide range if tide range is higher than critical value. Analyses of fresh and salt water mixing based on the experiments data uncovered the essence of the phenomena: ① The stratification is broken during the tide range changing, which changes the forces resulting in salt intrusion; ② Gain of salt is mainly due to the exchange flow if fresh water and salt water is stratified, stronger tide strength could damp the stratification and reduce the exchange flow salt flux, causes smaller salt intrusion length; ③ While if fresh water and salt water is mixing well, gain of salt is mainly due to diffusion, stronger tide strength could provide stronger diffusion, causes longer salt intrusion length.
Abstract: To better understand the wave-induced longshore currents in nearshore region, a numerical model is developed based on the second order fully nonlinear Boussinesq equations.The governing equations possess optimum linear properties and second order fully nonlinearity characteristics in medium water depths.The relaxation zone method is used to generate non-reflective and higher-order nonlinear waves, and the periodic lateral boundary conditions are imposed to mimic open sea boundaries.Utilizing the developed model, the effect of involved parameter values on the numerical results are investigated by conducting numerical experiments.Good agreements between numerical results and experimental data demonstrate the accuracy and applicability of the model.The effects of different wave conditions on longshore currents are also investigated numerically.
Abstract: The local inflow is an important factor affecting the accuracy of hydrodynamic models, but its value is difficult to determine and quantify in real-world applications.From the viewpoint of inverse problems, a method is proposed to determine the local inflow.Firstly, the continuity equation is integrated along the reach to have the analytic expression of inflow correction, and then the response function between the nodal stage and the local inflow can be obtained by numerical discretization.Finally, based on observed tidal data, the local inflow is evaluated by the iterative algorithm.A numerical experiment is conducted to validate the feasibility of the proposed method.Excellent agreement is obtained between the inverse values and the real ones as revealed by the deterministic coefficient of 0.996.The method is applied to the hydrodynamic modeling of the reach from Datong to Zhenjiang in the Yangtze River.The generalized process of local inflows in the reach is obtained and further refined.The result demonstrates the validity of the method.
Abstract: Main ions and hydrogen, oxygen isotopes were measured in samples of lake water, river water and spring water, which were collected from various locations of the Tajikistan region during the period from September through October 2011.The spatially distributed characteristics of these hydrochemical variables are analyzed to further explore the causes of formation and their environmental significance.The results show that the ion product of water can be used to represent the environment character in different areas of Tajikistan.Ca2+ and HCO3- are the dominant ions in lake water and spring water, which are mainly come from the calcite and dolomite weathering.Ca-SO42- and Na-HCO3- are found in few water samples resulting from the evaporation and silicate weathering.The lakes of Tajikistan are mostly located in the east mountainous area with the quality types of Mg-SO42- and Na-Cl-, impacted by long term evaporations.Slight saline and saline lakes are most common in the area induced by the arid climate condition.The hydrogen, oxygen isotopes of river and spring water in Tajikistan vary from -129.38×10-3 to -65.19×10-3 and -17.06×10-3 to -9.33×10-3 respectively.Spatially, these hydrochemical variables are enriched gradually from east to west, which indicate that the water supply of rivers and springs in the east is replenished by glacier melting and those in the west, precipitation is the main source of water supply.The relationships between hydrogen and oxygen isotopes of east and west river water are significantly different as the result of different sources of water supply.The variation of hydrogen, oxygen isotopes in lakes mainly reflect the amount of evaporated water from lake surfaces.
Abstract: China is a country facing water resources shortage in general and often coexists with droughts and floods. In recent years, the frequency of extreme hydrological events has been increasing, while the attenuation of water resources in the north became evident, the situation has turned out to be severe. On account of the hydrologic regimes in China, as well as the research practices on the coordinated routine and emergency management of hydrology and water resources in aspect of utilization of stormwater, strategic reserves of water resources, and water storage spaces, the paper promoted the concept of establishment of the coordinated routine and emergency management of China's hydrology and water resources. That is, combining routine management in the normal state with emergency management in the abnormal state base on the overall annual and interannual hydrological processes, to implement water resources management in the whole process of circulation of natural water cycle, so as to realize the integration of development and utilization of water resources, and flood control and drought relief, promote the efficiency of circulation of water cycle, and enhance the level of water security.
Abstract: The study reviews the advances of the last decade and summarizes the driving force of sediment resuspension and the coupling effect, the release mechanisms for phosphorus as well as possible influencing factors via sediment resuspension.Relevant researches on the subject show that the driving forces can be in the form of either acting alone or intercoupling.The latter is subject to a great deal of spatial and temporal variability.Reducible sediment suspends into oxic overlying water resulting in the removal of endogenous soluble reactive phosphorus (SRP) via oxidation reactions of Feand Mn and absorption of resuspended sediment particles.While endogenous organic phosphorus is transformed into SRP via biomineralization and photolysis.Factors, including sediment physicochemical properties, hydrodynamics, aquatic organisms and physiochemical properties of overlying water, can affect migration and transformation of phosphorus during sediment resuspension.It is proposed that future studies should improve the understanding of the multi-process coupling effect during endogenous phosphorus migration and transformation via sediment resuspension, transformation of sediment phosphorus forms as well as their bioavailability via resuspension, and mineralization and photolysis mechanisms of organic phosphorus and their regulating factors in frequently-disturbed waters.
Abstract: China frequently experiences large scale drought events.The latter have become one ofthe most important restraining factors affecting the socioeconomic development.Drought frequency analysis can reveal the characteristics of drought occurrences and their spatial and temporal distributions.Such an analysis is essential to the water resources planning, designing and management, as well as the risk-based management of drought disasters.In this paper, research progresses are systematically reviewed on the definition and identification of droughts and on the point to regional frequency analysis of droughts.The concerning issues are also reported on.In addition, the drought definitions applicable to drought frequency analysis are highlighted.The main problems in drought identifications are discussed.Three approaches for regional frequency analysis of droughts are summarized.Finally, it is proposed that the description and identification of droughts should take full advantages of the regional information on the hydrographical and meteorological characteristics, the atmospheric circulation condition, as well as the cause and extent of droughts.The basic theoretical issues in the distribution of variables, the drought return period and the empirical frequency need to be further studied.There should be paid more attention on the analysis of regional drought frequency and drought characteristics related to runoff, soil water and water system.