Abstract: The precipitation lapse rate (altitude effect of precipitation)and the zone of maximum precipitation in Tianshan and Qilian Mountains regions are studied using TRMM(Tropical Rainfall Measuring Mission)precipitation data.The results indicate that the annual TRMM precipitation compares well with the gauge observation over the two regions,the precipitation lapse rate and the zone of maximum precipitation can be quantified using the TRMM data.The annual precipitation in the Tianshan Mountain region is well correlated to the altitude over the two mountainous regions;the correlation coefficients are 0.90,0.81,and 0.58 on the Southern,Northern and Western slopes,respectively.The correspondmg multr-year average of precipitation lapse rates are 11.0 mm/100 m,6.3 mm/100 m,and 7.4 mm/100 m,and the zones of maximum precipitation on the three slopes are located at altitudes of 2200 to 3 500 m,3 200 to 3 700 m,and about 3 000 m,respectively.And in the Qilian Mountains region,the precipitation increase with the elevation,the effect of altitude on precipitation is more pronounced in the eastern part of the region compared to that of the western region.The precipitation lapse rate is 11.9 mm/100 m in the east,while,the zone of maximum precipitation is in the area with altitudes of 4 000 to 4 500 m.
Abstract: The parameters in the temperature-based Hargreaves method for the estimation of potential evapotranspiration(ETP)are calibrated by the FAO Penma-Monteith method and daily data during the period 1959-2008 at 20 meteorological stations in the Weihe River basin.To study the impact of(limate(hangs on potential evapotranspiration, the projected daily maximum and minimum air temperature(Tmax/Tmin)of HadCM3 CCM under A2 and B2 scenarios are first downscaled onto local meteorological stations using the statistical downscaling model(SDSM).Using the calibrated Hargreaves method,the future ETP,Tmax and Tmin time series under A2 and B2 scenarios can then be calculated.The spatiotemporal characteristics of these series are analyzed.Results show that the calibrated Hargreaves method reproduces well the observed potential evapotranspiration at each of the 20 meteorological stations;upward trends in daily Tmax and Tmin and annual ETP could be significant compared to that of the baseline period 1961-1990 under both scenarios;the increase in meteorological variables would be greater under A2 than B2;over different regions of the Wei River basin,the annual ETP could be gradually increasing for the three future periods,the 2010-2039,the 2040-2069 and the 2070-2099;and the greatest increase of ETP could be expected in the south bank of the basin, while the lowest increase might be found in the north bank.
Abstract: The performance of twenty-two General Circulation Models(CCMs)in simulating precipitation and temperature are evaluated and validated in the Yangtze River basin.Simulations of these CCMs were used in the IPCC Fourth Assessment Report(AR4).The Bjerknes Center for Climate Research(BCCR)Bergen Climate Model (BCM)2.0,or BCCR_BCM2.0,and other six CCMs stand out from the twenty-two evaluated CCMs.Using an artificial neural network and climate changs projections from the selected seven CCMs under A1 B,A2 and B1 scenarios, the hydrological response to future climate changs in the Yangtze River basin is studied.The projective on the subject is presented.The result shows that there could be a decreasing trend in the mean annual streamflow in the future.At the Yichang station,a dry year condition would be likely to become more common in a warmer world.The reduction of mean annual streamflew could reach as much as 520 m3/s for dry years,while such a reduction would be 250 m3/s for a normal year at the Datong station.The decrease in available water could be a bid challenge to the practice of water allocation and management in the western and central routes of the South-to-North Diversion project.The mean monthly streamflow would be projected to be increasing during January to June,while,the opposite should be true during the second half of the year.At Yichang and Datong,the streamflow increases would be 29.6% and 13.8% during,Tanuary to,Tune and decreases could reach as much as-18.2% and-11% during the second half of the year,respectively.The variation of streamflow could he expected to be larger at Yichang than at Datong.During flooding seasons,there would be a decrease of-8.5% in Yichang streamflow,and a slight incerease for other reasons.In contrast,the Datong streamflow would have a 2.3% increase during flooding seasons,and a slight decrease in non-flooding seasons.
Abstract: Setting ecological protection goal of Ulungur Lake is the foundation of the rational and efficient allocation of water reso nrees in this watershed.Baced on the characteristics of breeding of freshwater fish in cold water,the paper puts forward a new approach suitable for the lake in arid area on how to determine the lowest ecological water level subject to the relationship among the lake salinity,fishes and water quantity.According to the new approach,the ecological water demands for reserving the lowest ecological water level in typical years are calculated.The result shows that the lowest ecological water level of Buluntuo Lake is 476.12 m,while,Jili lake is 478.12 m.Deducting the precipitation and 400 million m3 of water diverted from outside river basin,there is still a deficit with an amount of 644 million m3,533 million m3,220 million m3 and 106 million m3 respectively by the year with precipitation frequency of 92%,81%,46% and the normal.Finally,an analysis on the reliability of results is done.
Abstract: Uncertainties associate with parameter estimation in modeling the water cycle can be reduced to a certain extent by expanding the utilization of modeling information and increasing the amount of data for parameter estimation.This is done through collecting and using the isotopic composition of water within the water cycle in model identifieation.In this study,the isotopic information is used to estimate the steady-state infiltration rate in Philip's two-parameter equation and the estimated parameters are validated through the indoor experimental data.The result shows that the estimated steady-state infiltration rate is in food agreement with the measurement.Analytical previsions of hydrogen and oxygen stable isotopes will have some impact on parameter estimation using isotopic information.
Abstract: In order to understand the effect of temperature on soil moisture movement and dynamic parameters, a combined study of laboratory experiments and theoretical analysis is conducted to examine the variation of soil moisture movement parameters due to temperature changes.The study involves the soil moisture retention curve, the hydraulic conductivity, the soil moisture diffusivity and the specific moisture capacity.Results show that soil temperature has a significant effect on soil moisture characteristics and soil structures.The effect of temperature variation can be quantified and described by examining the changes in soil moisture dynamic parameters.The effect of temperature changes on soil moisture characteristics is mainly through altering the kinetic energy and potential energy of the moisture, while on soil structure is mainly reflected in the potential energy of the moisture.Additionally, there has been a noticeable variation of the effect for different soils.The temperature effect on soil moisture movement can be neglectable for sandy soils,for clay soils;however,the opposite is true.
Abstract: Large-scale soil column experiments for simulation water-salt movement in clay interlayers under normal growing conditions were carried out in an easily-salinized region for different textures of soils and groundwater condidons in the Huang-Huai-Hai alluvial plain of China.In this study,the 20-year measurement was analyzed to examine the effect of clay interlayers on soil water-salt movement in easily-salinized regions.Results show that the clay interlayer has a significant positive effect on the water-holding capacity in the soil and acts as a filter obstructing the salinity infiltration.This is especially true for restraining the penetration of surface accumulated salts.The thicker the clay interlayer is,the greater the effect will he.The range of depth to groundwater is likely to he smaller in the area with surface accumulated salts and clay interlayers around 1.0 m than that with silt loam soils around 1.5 m.And in the latter case,the salinization of soils is easily induced when the groundwater level is lower than a threshold value of 2.5 m.The amount of accumulated salts is found to be higher in clay interlayers than that in silt loam soils.Thus, proper monitoring and measures are necessary to prevent the secondary salinization of soils in the practice of water resources management.
Abstract: The riverbed morphology is quantitatively evaluated using the generalized data from flume experiments to calculate the fractal dimension of riverbed surface(hereinafter referred to as the BSD).Discussions are given on the method of BSD calculations,on the fractional characteristics in meandering channels,as well as on the relationship between the BSD and the bed form resistance.The result shows that the BSD value is able to represent the longitudinal change in talweg,transverse geometric changer in foreshores and deep channels.The scouring and silting extent or bending river bed surface,exhibits clear fractal characteristics.BSD can be used as a measure of the bed surface roughness height.The relationship between the BSD and the bed form resistance is thus established.The bed form resistance is proportional to BSD.There are two distingue regions in the different relationship between the BSD and the bed form resistance,and can be identified by flow rates.
Abstract: Since traditional methods to measure bed shear stress fail to world in the presence of seepage,alternative approaches to study the response mechanism of bed shear stress to seepage are limited to some theatrical analyses with some assumptions and indirect estimation.The issues of whether seepage reduces or enhances bed shear stress are still matters of considerable debate.To this end,a special-designed device is deployed to directly measure the bed shear stress in the open channel flume with varying seepage rates.Experimental results show a close relationship between changer in bed shear stresses and the relative seepage intensity vs/U.Variation in bed shear stresses with seepage has an inflexion and a critical value when the |vs/U| is about 0.2% and between 0.2% and 0.4%,respectively.Therefore,it is clear that the range of vs/U investigated experimentally is the leading cause of the contradiction in the literatore.
Abstract: A coupled 1 D-2D numerical model for simultaneous hydrodynamic simulation of river-lake systems is presented.The Water Stage Prediction-Correction(WSPC)method,which is originally proposed to treat the inter-reach coupling at junctions in river-network hydrodynamic calculation,is adopted herein to treat the inter-model connection conditions between 1D and 2D models at the coupled boundaries.Under the WSPC framework,the execution processes of 1D and 2D models during each time step are totally independent,implying that we can male use of the existing model at a minimum modification.Compared to traditional decoupling techniques,the WSPC method gives the advantage of fully fulfilled inter-model connection conditions,whose accuracy also may be controlled by tuning the numeric tolerance.The proposed model is verified by hypothetical and practical cases,and the results show its reliability and good prospects in application.
Abstract: Accuracy and efficiency are two key factors for the numerical simulation of N-S equations in computational fluid dynamics.In this paper,the Eulerian-Lagrangian alternating direction implicit(ELADI)finite difference method for 2D shallow water equations in orthogonal curvilinear coordinate system is extensively discussed together with the basic principle and discretization methods.The ELADI method combines the alternating direction implicit method (ADI)with the Eulerian-Lagrangian Method(ELM).The numerical diffusivity of the ELM method is analyzed.The ELADI method is compared with traditional methods using the laboratory experiments conducted in a curved flume,as well as field measurements from the Haoxue river bend in the upper,lingjiang Reach of the Yangtze River.The result shows that the ELADI method improves computational efficiency greatly with satisfactory accuracy.For the test case, ELADI even allows the Courant number reaching 40 and reducing the computational cost by 90% compared to the traditional method.
Abstract: Correctly describing the flow process near the breach site and the variation of breach discharge is essential to the prediction of overtopping flow and flood propagation,which provide valuable information for breach blocking and disaster preparation,as well as flood damage assessment.Based on the observational result from a series of bend flume experiments,the erosion process during overtopping breaching of non-cohesive embankments can be divided into four stages,overtopping,groove formation,breach stretching and stability.The analysis involves the variation in water levels and flood discharge in the river after overtopping breaching,the water-level difference between the inner and cuter river,and the influence of embankment materials on water-level changer near the breach site.Finally,the study snmmarizes the relationship among the breaching discharge,the breach width and the water head near the site.
Abstract: Sediment deposition in Three Gorges Reservoir(TCR)is likely to increase significantly after the filling of TCR.The causes of reservoir sedimentation pattern in the vicinity of Three Gorges Project(TCP)during the early filling of TCR are examined using the observed data and a 3D mathematical model for flow and sediment transport.Results show that the sedimentation characteristics in the vicinity of TCP are not only related to the 3D properties in flow patterns,but also related to the characters of deposited sediment particles during the early filling of TCR.The formation of fluid mud is the result of deposited fine sediment particles in the vicinity of TCP during early filling.The particle is in a fine form and the initial dry unit weight of deposited sediment is also small,which exhibit a typical feature of fluid mud.The sedimentation volume value nearby TCP is tremendous due to the lower flow velocity.The deposited sediment particles in the form of fluid mud slide move downward to the lowest position of cross-sections under the influence of gravity,and then accumulate there in a horizontal form following the thalweg line.
Abstract: It would he beneficial to better understanrl the emission conditions through measuring the greenhouse gas (CHG)emission from the Xiangxi River,an anabranch of Three Corges Reservoir,as well as to study the influence of the alga bloom on the CHG emission.Using floating chambers,CO2,CH4 and N2O emissions from the Xiangxi River were measured by 11 times field observations from October 2009 to October 2010.The observational result shows that the average CO2 emission is 76.52mg/(m2·h),and the intensity is negatively correlated to the chl-a concentration.The CO2 intensity falls below zero during the alga bloom,showing absorption.While the CH4 and N2O emissions,the average values are 0.244 9 mg/(m2·h) and 0.011 7 mg/(m2·h),respectively.Compared to the resuits of other studies in various regions of Three Corges Reservoir,the average CH4 emission from the Xiangxi River is low,which is obviously different from the(alculation based on some international approach based on the average for the entire region of the reservoir area.
Abstract: To investigate the influence of the operation of the Three Gorges Reservoir (TGR) on the salt water intrusion (SWI) from the North Branch (NB) to the South Branch (SB) of the Yangtze River estuary (YRE), a study was conducted by analyzing salinity observations before and after the TGR operation.The results indicate that SWI from the NB of the YRE started earlier in a typical year; the intensity of SWI increased from October to November, while it reduced from December to April of the next year due to the operation of the TGR; the reduction rate of the intensity of SWI is much less than the increasing rate; during the period from January to April when SWI is the most serious and the intake of fresh water from the YRE is the most important, the reduction of SWI is not great enough, so the effect of the operation of the TGR is not significant during this period; the operation of the TGR has little effect on the reduction of SWI of the whole year, but it has reduced the intensity of the most serious SWI from the NB to SB, which can contribute to the safety of the supply of freshwater in the YRE area.
Abstract: To understand the influence of dams on connectivity of riparian plant communities,three small hydropower plants from up-to-downstream of Modaoxi River were surveyed in September 2008.Plant samples were taken from the small hydropower plants,as well as at the upstream dams,downstream dams and downstream outfalls.Species richness and biodiversity of herbs and shrubs were determined in consecutive 1 m2 quadrats and 25 m2 quadrats,respectively,along a 50 m long belt transect.157 plant species were recorded on a total sample size of 63 quadrats.The resuit shows that the construction of small hydropower plants has significant impacts on river physical variables(such as current velocity,water depth and substrate types)along the nine sampling locations.The riparian plant community has been more or less affected by the dam construction.The overall species richness and herbs varied significantly in different locations.In contrast,the variability in trees and shrubs is found to be insignificant.Local differences in species diversity are also significant.Hygrophyte species richness has been found to be greater in the upstream and outlets than that of in downstream.The construction of small hydropower plants has disturbed the continuity of riparian plants and has a negative impact on the protection of the plant diversity in the river.
Abstract: An experimental study was conducted in an indoor soil tank to examine to nitrogen infiltration and movement through unsaturated soil in topsoil layer of riparian zone.The timing of seepage flow from the tank and the seepage sequence at different sampling points were monitored.The variation of nitrogen concentrations(e.g.,total nitrogen TN and ammonia NH4+-N)was also observed.Results show that the vertical velocity of percolation water is larger than the horizontal one during infiltration into the unsaturated topsoil layer of riparian zone.In the process from dry-towet and wet-to-dry,the TN and NH4+-N concentrations first has a sharp increase and then gradually decrease until reaching a stable state.This is true for every monitoring point.In addition,the nitrogen retention capacity in the topsoil layer of riparian zone is high under unsaturated conditions.Along the 1.08 m long slope and 11 hours after the experiment began,the TN and NH4+-N、oncentrations at points 12cm below the surface reduce by 74.23% and 68.02%,respectively.
Abstract: A Y-shape apparatus,which stimulates the resuspension-sedimentation process of indoor sediment,was deployed to study the resuspension and settlement process of sediments from the estuary of Tianji Port in Conghu Lake under the influence of different wind strengths.More suspended substance(SS)will be released into the water the increases of wind speed.The increment of ammonia nitrogen(NH4+-N)is negative under the three types of wind.The gross of phosphate(PO43--P) exhibits a decreasing trend under the condition of light to moderate wind.The gross of PO43--P rises significantly under strong wind,about the increase of 46% compared to the initial value.The release and adsorption of PO43--P are dynamically balanced under a simulated wind condition between 5.1 m/s and 8.7 m/s and an apparent value equals to the initial value.The gross of total nitrogen(TN)and total phosphorus(TP) Increases as the wind strength gets stronger.Compared to the initial value,the increase of TN and TP can be as much as approximately 2 and 17 times,respectively.The gross of TN and TP almost returns to the initial value after wind stops.For the typical type of wind,the vertical distribution of nutrient shows not clear patterns.
Abstract: Sediment resuspension characteristics are studied using the laboratory wave flume with different sediment bulk densities(1.34g/cm3,1.47 g/cm3,1.55g/cm3 and 1.59g/cm3)and wave hydrodynamics.Results show that the vertical concentration of suspended sediments is almost uniform without the influence of wave action.Only local sediment resuspension can be observed for small wave amplitudes.The vertical variation in suspended sediment concentrations is insignificant.When the wave height reaches 9cm,the bottom shear stress will be much greater than the critical shear stress.Thus,there will be a sudden increase in suspended sediment concentrations.The concentration will be 10 to 15 times higher than that for small wave amplitudes after 10 minutes.The resuspension quantity can account for about 80% of the gross resuspension within 60 minutes.Large variations are observed in the vertical profile of gross resuspension.The bulb density is highly correlated to the gross resuspension.The larger the bulb density is,the smaller the gross resuspension will be.
Abstract: According to the descriptive-explanatory-humanistic ideological system,the three main routes of evolution course in hydrological sciences were summarized from the following three dimensions:problems,disciplines,and methodologies.It can be seen from the dialectical analysis amongst different stages along the routes that the intersection of the main routes will generate the new frontier directions in objects of study,scientific recognition,and technical innovation for the field of hydrology.This paper also discussed and remarked the relationship between empirical method and theoretical formula,the compatibility between deterministic and stochastic approaches,in view of hydrosphere complexity around the Earth.Finally the authors emphasized the significance of the research on water cycle routes/processes organization by means of the organization of various sorts of logical thinking modes,because of hydrological variability,system diversity,changing environments,and more uncertainty in the real world.