Abstract: Using daily rainfall data at 738 stations in China from 1951 to 2004,and defining the 95th percentile as the threshold of extreme precipitation for each station,the characteristics of the spatio-temporal distribution and the linear trend of extreme precipitation events with different durations are analyzed.Results show that the frequency of extreme precipitation events is higher in the regions south of 35°N than in other parts of China,especially in the midlower reaches and the southern parts of the Yangtze River and in the southeastern part of the Tibetan Plateau with longer duration.And it happens more in summer than in other seasons.It is found that the frequency decreases rapidly whereas the mean intensity increases with the increase of duration of extreme precipitation events,especially in eastern part of China.The trend analysis shows that there is an increasing trend for regionally averaged relative frequency but a decreasing trend for the mean intensity of 1-day extreme precipitation events.They both increase significantly in the mid-lower reaches of the Yangtze River,in South China and in eastern Plateau and decrease significantly in some parts of North and Southwest China.The frequency and intensity of the extreme events lasting more than-days show a similar spatial distribution with that of 1-day events,but show no significant trends for their regionally averaged values.
Abstract: There exists ponding water during rainfall or irrigation inducing runoff into the unsaturated soil of farmland,and the soil chemical is lost into the surface runoff.A two-layer system model is established to describe the chemical transfer to surface runoff.An analytical solution for the model is obtained based on the chemical conservation laws and water balance equations,and the unsaturated soil experiment shows that this two-layer analytical model is reliable and reasonable.The effects of various soil properties on the chemical transfer to surface runoff are discussed by sensitive analysis of some parameters of the unsaturated soil in the model and experiments.It is found that higher adsorptivity of unsaturated soil will reinforce the ability of the soil chemical transfer to surface runoff,but the soil with greater bulk density decreases and higher initial volumetric water content of soil increases the soil chemical transfer to surface runoff.
Abstract: In this paper,the distribution and total amount of evapotranspiration (ET) is estimated under the diverse landscape over the Heihe river basin in Northwestern China in July 2004 by using MODIS data and meteorological data based on the aerodynamic method and the time upscaling scheme.Taking advantage of the high resolution Landsat-TM data,according to the contrastive analysis,we find that the influence of the heterogeneous underlying earth's surface on the estimation of water and heat exchange on the land surface by using the high resolution remote sensing data is obviously smaller than that by using the middle resolution ones.By comparing the estimates of ET with the observation data collected from "JTEX" experiment we conclude that,by using the high resolution data,the parameterization algorithm used in this paper can derive daily ET with a relative error of 10%.After analyzing the distribution of the derived monthly ET over the basin in July 2004,it is concluded that the mountainous area above 2000 m exhibits the ET twice more than that the area fronting mountains below 2000 m elevation; and the oasis and crop area take on an ET 12 times more than that of the desert and Gobi region over the area fronting mountains,and the former is the most significant region that consumes land surface water over the mid-downstream area in summer.
Abstract: In the absence of the long-term observations of the components of the water and land surface energy budgets,modeling can provide consistent fields of the land surface fluxes and states.We simulate the components of surface energy balance (SEB) equation using the land information system (LIS) of the global land data assimilation scheme (GLDAS) during the period of Novenben 2002 to Decenbero 2003 in China.The residual analyses of SEB indicate that the residuals distribution (RD) shows some spatial and temporal characteristics.The temporal characteristics of the RD suggest that LIS can simulate energy flux better in spring and summer than in other time.The spatial characteristics of the RD indicate that LIS can simulate energy flux better in places with relatively low latitude or low altitude than in the places with either the relatively higher latitude or higher altitude.This kind of the temporal and special distribution pattern is probablv related to the parameterization of snow albedo.The results of the comparison between simulated DLDAS and MODIS land surface temperature (LST) indicate that the main difference between two LST are within ±5 K.The scatter plots and standard deviation suggest that the simulated LST of night is 2-3 K more accurate than that of day time.
Abstract: This paper proposes a reservoir flood dispatching mode and method based on the case-based reasoning (CBR) techniqnes with the artificial intelligence (AI).By adopting relational database to resolve the representation,organization,index and storage of the flood dispatching cases,a database related to reservoir flood dispatching case is built.Based on the combination of the genetic algorithm and tabu search and nearest neighbor algorithm,a hybrid approach is constructed,improring the speed and quality of the case retrieval.The strategy of the case modification and study is presented by using the genetic algorithm to optimize case characteristics weight and adopting the multi-objective decision method to optimally select the case.Finally,the reservoir flood dispatching system based on CBR is developed.The research shows that for the reservoir flood dispatching the case-based reasoning method provides a new thought and method to simplify the knowledge acquisition,improve the efficiency and quality of dispatching,accumulate and reuse the knowledge concerned.
Abstract: To study the probability hydrological forecast and its application value,the Bayesian statistic forecast theory is adopted to formulate the reservoir middle-and long-term runoff forecast model,which describes the uncertainty of hydrological forecast by the distribution function.The gray correlation prediction model for the meteorological factors is presented to count the uncertainty of the input factor.The real-time meteorological information and history hydrological data are coupled effectively,which breakthrough the limitations on the information utilization and samples concerning the determined forecast method and improve the accuracy of hydrological forecast.The established model is tested on the runoff forecast of the Feng-man reservoir.The application results fully show that the superiority is apparent compared with the conventional forecast method.Not only does the model benefits the user to consider the uncertainty quantitatively in decision-making,but ulso improves the forecast accuracy expectatively.
Abstract: Urban rainfall-runoff model plays an important role in water resource management.Based on the storm water management model (SWMM),a drainage simulation system is established in Yalianfang catchment of Macau.The generalized likelihood uncertainty estimation (GLUE) approach is selected to analyze the parameters uncertainty of the complex rainfall-runoff model.Latin hypercube method is used to obtain sample sets,and Nash-Sutcliffe efficiency coefficient is used as the criteria of assessing the fitness between monitored time series and predicted one.The uniform pattern is determined as prior distribution of parameters.The results show that GLUE method is an efficient method to analyze parameters uncertainty of rainfall-runoff model,and the analysis results can offer information for further understanding to the modeling system.
Abstract: In coupling model of hydrology and hydrodynamics,the inaccurate calculation of hydrology model is the cause of the discrepancy between the lateral inflow of hydrodynamics and practical case,so the lateral inflow is updated by using the inverse analysis based on the principle of water balance.With water stage and discharge being state variables,the systematic state equation of Kalman filter is set up based on the Saint-Venant equations solved by the four point linear implicit form.Through the inverse analysis,the unbalance of water stage and discharge are put back to the lateral inflow and adjusted,then the updating water-inflow in forecasting period.The inverse analysis method of the interval inflow is applied to the flow calculation for the river section from Cuntan to Wanxian of the Yangtze River,adopting the flood information of construction period with reservoir storing water as high as 135 m and river section from Datong to Zhenjiang with hydrological information of 1998.The forecast of 6-hour lead time proves that the performance of the inverse analysis method is feasible.
Abstract: A series model method is adapted to the preliminary study of scale effect of discharge atomization-rainfall (A-R) model with the field observation result of discharge atomization for Wujiangdu power station.The effect of Re and We numbers of flow on the A-R intensity is analyzed.A conversion relationship of A-R intensity between prototype and model results is developed.The similitude criteria of the A-R range followed by discharge atomization model is discussed,and the conclusion is achieved that the surface tension of discharge A-R model is ignored when We number is larger than 500.
Abstract: Based on the study of the hydraulic characteristics of the aerated flows,the theoretical calculation of the aerated water depth and the energy dissipation rate is derived by using the momentum equation on the pre-aerator stepped spillway.The relationship of the aerated water depth and the energy dissipation rate with the step sizes can be obtained theoretically through the equation.The calculated results agree well with the experimental date and are applied to the practical projects.The results indicate that the pre-aerator stepped spillway has the advantage of the easy control of the concentration of the aeration near the bottom floor,ensuring the sufficient aerating of the high energy dissipation rate in the bottom area,and suitable for the project with large discharge rate.This study provides the theoretical and experimental basis for the extension of the earlier study of stepped spillway design.
Abstract: Less attention if paid to the study of the sediment surface morphology and the adsorbed pollutant.In this paper,the field emission scanning microscope is used to measure the surface microscopic morphology of sediment particles and detect the location of the adsorbes copper ions.And the surface curvatures of the copperions absorbed are computed to analyze the adsorption characteristics on sediment surface.The results show that the copperions are mainly distributed in the ridge and valley of the particle surface and fewer ions are located in the other textures of the sediment surface.The curvature Cu reflects the adsorption capacity of copperion on the complex surface.The area with Cu = 1.1 has great potential to adsorb copperions.
Abstract: Based on the multiple observation methods,we conducted a field study at the Chongming Dongtan salt marsh in July 2007.The collected data is analysed systematically in this paper.The observation results show that (1) Time variation of the creek water level at field site is different from that of the coastal sea,which might be affected by the damping of the creek and marsh surface.The rising phase is steeper than the falling phase one.During the ebb period of the creek current,the rise of the local water table is not likely related to the tidal water entering creek.It banks up while the ebb creek water met the rising tidal water.(2) Wind plays an important role in hydrodynamics of the salt marsh.While the tidal wave is entering inner marsh,the shoreward wind will updrive water table compared with the offshore wind.(3) The creek current velocity is not strongly related to the rate of water level changes in the creek or the rate of the coastal tide fluctuation.And (4) the wetted cross-sectional area of the creek is relatively small,while little water is in the creek.Once the reversal creek current occurrs,one creek current velocity surge turns up.Due to the expansion of the wetted cross-sectional area,a creek current velocity surge exhibits as the creesk water spills out to marsh surface.The creek water level descreases slowly during the ebb tide.No creek current velocity surge presents as the marsh surface water flows into the creek.Finally,this paper summarizes the factors affecting hydrodynamics in the salt marsh,and gives the suggestions on the future works.
Abstract: Monthly mean sediment load and runoff changes in the past 40 years are analyzed at Pingshan station,Yichang station,Datong station and Hankou station along the mainstream of the Yangtze River basin and Beipei station in the tributary of the Yangtze River basin,with the help of wavelet transform method.The results indicate that:① the wavelet transform method is the proper method for detecting the influences of water reservoirs on transportation of sediment load and runoff changes.The influences of water reservoirs on sediment load are more serious that those on runoff changes; ② Gezhouba dam exerts less influences on runoff changes and sediment load.The down-cut of the riverbed occurrs after the operation of Gezhouba dam,but this influences are not enough to remove the 1-year-period of runoff and sediment load changes; ③ The Three Gorges dam exerts increasing influences on sediment load transportation,removing the 1-year-period sediment load of sediment load changes,but shows no influences on runoff changes.The influences of Three Gorges dam on sediment load are adverse to the distance to the Three Gorges dam; ④ The influences of water reservoirs on sediment load and runoff changes is related to the size of the river catchment.The sensitivity of influences of water reservoirs on sediment load is less in the larger river catchment.
Abstract: The field investigations and an experiment were conducted in the Juma river in the suburbs of Beijing to study the effect of habitat fragmentation on river ecology,using benthic macro-invertebrates as indicator species.Three experimental plots were isolated from a relatively undisturbed stream habitat with sheet iron.The benthic assemblages and water parameters were measured by sampling periodically.The results indicate that the abundance,taxa richness and biodiversity of inverte-brates significantly decrease in the experimental plots owing to the habitat isolation.The smaller the experimental habitat plot,the more significantly these biotic indices decrease.The contents of the dissolved oxygen in the studied plots present the inconsistent variations.The comparison of the benthic communities shows that the relative abundances of Ephemeroptera and Diptera reduces significantly in the isolated plots,and that of the Odonata and Lamellibranchia increase significantly.It is also found that the benthic communities need some time to stabilize after isolation,and then present apparent variation over time.There is a relatively high degree of taxa turnover between isolated plots and the non-isolated reach,which can be attributed to the flight and dispersal of many aquatic insects in their adult stage.However,the benthic communities in isolated plots are not nested subsets in the natural non-isolated stream.This paper also gives some suggestions of the river restoration and the preservation of river ecological integrity based on the study and the present status of the rivers in China.
Abstract: Using a mean age concept defined by Deleersnijder,we apply the three-dimensional hydrodynamic and eutrophication model HEM-3D to investigate the pollutant age distribution under different river discharge conditions in the Pamlico river estuary (PRE),North Carolina.The model results reveal that it takes about 65 days for pollutant to be transported out of PRE during normal season,while,it takes 230 days and 20 days for pollutant substances to be transported out of PRE during dry and flood seasons,respectively.The time differences indicate that the transport process is a function of river discharge.The spatial variation of the pollutant transport age is significantly affected by the salinity intrusion in the PRE; the later forms a salinity front at its most upstream location.The front inhibits the outward transport of pollutant.The salinity stratification plays an important role in the vertical distribution of the pollutant transport age.The vertical difference in age is enhanced as the salinity stratification increases.
Abstract: In order to study the effect of nitrogen (N) input of snowfall on the Deyeuxia angustisfolia wetland ecosystem in Sanjiang Plain,the snowfall,snow-pack,snow melting-water and leakage solution of soil (0～10 cm) were monitored from November 2006 to April 2007.The results show that the seasonality of the N concentration in snowfall is evident,and influenced by the manifold factors.The deposition of TIN,TON and TN in snowfall are 0.375,0.591 and 0.966 kg/hm2 in winter,respectively.The snow-pack reservoir determines the N reservoir.The NH4+-N and TON are the main body of TIN and TN in the snow melting-water,respectively,but the NO3--N and TIN lose more easily than NH4+-N,TON,respectively.The interceptions of TIN,TON and TN are 1.53,0.1 and 1.63 kg/hm2 by soil (0～10 cm) respectively.The nitrogen input of snow melting-water has directie ecological signification which stimulates growth of the plant and the microbe in soil.
Abstract: The mires in northern Great Khing'an mountains are particular with high latitudes and high altitudes.A Logistic regression model is developed to analyze the relationship between mire distributions and 18 eco-factors (including 11 topographic and 7 climate factors).The future potential distributions of mires are predicted under CGCM3,and the landscape changes are calculated by Fragstats software.The Logistic model has high prediction precision (ROC=0.96).The prediction results show that:by 2100,under the SRES B1,the potential mire area will decrease about 54.16%,and mires will disappear in the south of the flat hilly regions and intermontane plains; under the SRES A1B,the potential mire area will decrease about 59.62%,and mires in south forest regions will disappear; under the SRES A2,the potential mire area will decrease about 73.51%,and mires will be found only in the north area with higher elevations.In addition,the mean patch areas,landscape shape indexes and aggregation indexes will reduce,which means that the mire distribution will shrink from edges to centers and tend to be fragmented with simple patch shapes.
Abstract: In the paper,Wuliangsuhai lake,located in the arid area of North China,is taken as a case,in consideration of the characteristics of the shallow depth in the arid area.Through the relative analysis of one,two and three times' real-measured depth data and the reflectance of satellite images,the water depth is estimated based on the logarithm or non-logarithm model of five-,three-,two- and one-variable using the Landsat TM/% ETM data and the real-measured depth data from 2002 to 2004 according to the principle of water depth remote sensing.By model comparison and error analysis,the non-logarithm model of five-variable with three-time mesured data is selected as the optimal depth model.The model uses the multi-spectral composition method to estimate water depth,solving the problem that the single spectral can not reflect the spatial changes of submerged weeds,reeds,water color and bottom matter.The model accords with the characteristics of shallow lake in the arid area and can provide the new approach and reference for the other lakes of the arid area.
Abstract: An unstructured numerical algorithm of Roe's second-order upwind is proposed to solve the 2D tidal in the sea field of the Shengli oilfield.In order to make the Roe format practiable in the calculation under complicated geography condition,the Ropers method is used to deal with the term of bed slope source in the equation,so that the flux can be balanced.The method of step by step is used to calculate the friction source terms and enhance the stability of calculation.The mathematical model is successfully used to the Shengli oilfield waters,and gets better results.
Abstract: Cylinder is one the most common onshore or offshore marine installation.Aalculating appropriately the wave loads acting on the cylinder is important.The paper studies the calculaton of wave force on large scale cylinder.Using the linear wave diffraction theory to compute wave force on the large scale cylinder,the paper presents a Nyström method to solve the problem of the linear wave diffraction.The mathematical model for the linear wave diffraction is transformed into a two dimension Helmholtz equation by the airy wave theory.And the Nyström method is used to solve the Helmholtz equation.The numerical examples illustrate its accuracy.
Abstract: In this paper,a new method is presented to provide the tidal model under open boundary condition,in which the theory of the data-driven model is integrated with the tidal model,and the tidal current field data is imported,too.The approach constructs solution space of internal observation site with the results of numerical simulation cases,and describes the relationship between the internal observation site and the open boundary.And the filed data are imported into the relationship to inverse the open boundary condition.A case study of K1 tidal constituent amplitude in Liaodong bay is presented for the validation of the method.The maximum error of K1 tidal constituent amplitude is 0.008 m,and the results show that the method is efficient for inversing the open boundary condition.
Abstract: The linear solution always plays a leading role in theory construction.As the present studies on the short-crested waves are involved in the wide wave-current interactions,considering a typical coastal wave condition concerning both obliquely incident waves on and reflected ones off the coast barriers with the strong longshore current influence,a general linear sys tem on finite depth short-crested waves is developed,and the general solution and the special ones in both the deep-andshallow-waters are acquired only to improve the existing linear water wave system and providing a reliable base for the investigations of the nonlinear short-crested waves on wave current interactions.
Abstract: Based on the analysis of the structure characteristics and definition of the riparian buffer strip,the primary mechanism to control the rural non-point pollution is discussed from the following aspects:(1) reducing the speed of surface runoff,filtrating and barring the particulate contamination; (2) assimilating dissoluble contamination by vegetable and soil; and (3) facilitating denitrification.Research progress in the fitting width of the riparian buffer strip is discussed,and a view is put forward that the study on the fitting width of the riparian buffer strip only from the point of environment is far from enough in China and the integrated study is necessary for the fitting width of the riparian buffer strip from the point of environment,economy,society,etc.In the end,the future progress in purification mechanism of the riparian buffer strip is prospected.
Abstract: The cumulative environmental impact is one of the most important components in the environment research.The essence content of defining cumulative environmental impacts is put forward based on the review of the connotation including the cumulative environmental impacts sort and the concept's generation and development; the research in cumulative environmental impacts is conducted abroad for a long time and there are some problems,such as the concept inconsistency,the poor quantity of method and the lack of recognization.In China research in cumulative environmental impacts concentrates more on the analysis methods,but less on the definition and examples since 1990s.Then several analysis methods are classfied by the different application conditions.Especially,the research status of cumulative environmental impact assessment in water resource subject and the cumulative environmental impacts' characteristic in cascade hydropower exploitation are introduced in this paper.And four research trends are proposed.