Abstract: Biofilm colonization on sediment particles can have a significant effect on particle incipient motion.A series of flume experiments was conducted on two types of sediments,one of which was immersed in deionized water,and the other was cultivated in a mixture of natural water and nutrient solution.The result shows that the two sediment types can result in a significant difference in incipient motion.The incipient velocity of cultivated sediment varies over time.Sediment cultivated in natural nutritious water has a higher stability due to the biofilm growth.The incipient velocity increases with time until reaching a critical threshold,at which the optimum condition for biological activities is obtained,and then decrease.It is erect,especially in polluted water indicated that the role of microbes in sediment incipient motion needs to be consid ered,especially in polleted water bodies.
Abstract: The sediment incipient motion can be significantly affected by the presence of microbial biofilm growth.Using the experimental incipient velocity data collected under the influence of biofilm colonization,the incipient velocity formulas for the two types of sediments are derived for sliding and rolling motions.The thin water film theory is utilized to describe the coheslve force between sediment partmles and the aClheslve force generated by the biofilm in the formula derivation.Time variation characteristics of the biofilm strength and the feature of the substrate are also taken into the consideration.The result shows that both rolling and sliding formula are able to reproduce the observed incipient Veloci1t1es.The two calculated velocities are basically consistent with each other.
Abstract: Using a simple water balance model,monthly runoffs were simulated for 21 catchments with different climatic conditions in China.The sensitivity of runoff to climate changs in these catchments was further studied for hypothetical climate changs scenarios.Results show that monthly runoffs can be well simulated by the simple water balance model,the Nash-Sutcliffe coefficient on these catchments are greater than 65% and the corresponding average relative errors are less than 1%,and there is large spatial variations in the sensitivity of runoff in response to hypothetical climate changs scenarios.It appears that runoff is most sensitive to the changs in temperature and precipitation in arid and semi-arid catchments over the north Yellow River region,the sensitivity is less significant in humid and semi-humid catchments over regions of Central and South China,while almost no sensitivity in alpine regions in West China.Thus,the climate changs adaptation in the water sector should focus on arid and semi-arid regions in China.
Abstract: Using precipitation retrieved from Tropical Rainfall Measuring Mission(TRMM) and 31 meteorological stations surrounding the areas in 1998-2008,a series of spatial and temporal distribution of monthly precipitation is constructed for Tianshan Mountains.The series is validated using the crocs-validation method.The Nash-Sutcliffe coefficient is greater than 0.5 and the corresponding correlation coefficient is higher than 0.9.The result illustrates the applicability of using TRMM satellite to monitoring precipitation in northwestern China,especially in mountainous regions with insufficient meteorological stations.The precipitation series can be used to drive distributed hydrological models for water resources studies.
Abstract: Flood coincidence probability analysis among different regions is quite important for flood design and controt.The current flood coincidence probability analysis is based on the simple statistical analysis of observed data without theoretic methods.In this study,the daily flow data of four hydrological stations in the upstream Yangtze River and its tributaries,including the Pingshan at the Jinsha River,Caochang at the Min River,Beibei at the,lialing River and Yichang at the Yangtze River,are selected for case study.Multidimensional copula functions are introduced and used to construct the joint distributions of flood occurrence dates and magnitudes.Flood coincidence and conditional probabilities among the upstream Yangtze River and its tributaries thus are estimated.The calculated flood encounter values are compared to the empirical ones estimated by the observed data.The results show that the proposed method is rational and provides a new approach for flood encounter analysis.
Abstract: Shortage of water resources is likely to result in conflicts among the water resources supply and demand system the socio-economic development and the eco-environmental requirement.In this study,the principle of order is used to balance and coordinate the three conflict parties.This is done through the introduction of order parameters to the three parties.A system identification model is developed based on the concept of the degree of order and coordination.The results to the Dongjiang River Basin to reveal the evolution of the water resources supply and demand system.The results show that the water resource supply and demand of Dongjiang River Basin has evolved towards disorder and chaos state under the strong disturbance of human activies in 2000.
Abstract: The extraction of hydrological information from Digital Elevation Models(DEM) is an initial step in the application of spatially distributed hydrological models.Although,many automated methods have been proposed to extract the drainage structure from DEMs,the realistic river network and watershed boundary may not always be derived from conventional DEM processing methods.As a result,enhanced (or corrective) approaches have been proposed to improve the performance of existing single flow direction (D8) algorithms.However,those corrective measures may not always work over flat regions where the great uncertainty exists in DEM.Ambiguities in flow direction and parallel flow paths may arise if the surrounding cells have the same elevation as the central cell.In this paper,to downscale the DEM and extract drainage structures and watershed boundaries with improved accuracy a new method is proposed based on the Rural Infrastructure Digital Elevation Model is able to incorporate ancillary data and take into consideration of anthropogenic land cover features(i.e.roads and streams,buildings,some ponds and pipe systems) that influence drainage patterns.The method is applied to a watershed in the Shanghai drainage basin.The watershed can be characterized as a flat area undergoing a rapid urbanization process.The delineated maps and extracted stream networks are compared to those of using traditional methods.The result shows that the proposed method is able to produce more realistic results.The method is effective and easy to implement.
Abstract: Using monthly precipitation and temperature data from national meteorological stations and a digital vector map of modern glaciers from the Chinese Glacier Inventory,the glacier mass balance and glacier runoff in 1961-2006,in the Hexi Inland River Basin (HIRB),China,are estimated based on a monthly degreeday model and compared with the observed data.The results suggest that the modified monthly degreeday model can simulate the longterm changes in glacier mass balance and glacier runoff.It was found that the mean annual glacier mass balance during 1961-2006 was -49.5 mm per year.In the west of HIRB,the glacier exhibited slight negative mass balance; while glaciers in the east experienced serious mass loss.The average annual glacier runoff was 1.02 billion m 3 in 1961-2006.Over the entire basin,glacier runoff accounts for 14.1% of the total river flow.The prominent glacier runoff occurred in the Shule River and Danghe River,which accounts for 31.5% and 41.7% of the river flow,respectively.The results also show that glacier runoff accounts for 22.9% and 5%-15% of the river flow in Beida River and Heihe River,respectively and Shiyang River was less than 10%.Glacier runoff and its influence on river flow have increased in the last 46 years over HIRB.
Abstract: To study the evapotranspiration regularity over the Phragmites Australis wetland,the field experiments were carried out in a test field of the Liaohe Estuary.The evaporation container with water supply was installed to measure the evapotranspiration from the Phragmites Australis wetland,and the transpiration was measured using A PM-5 porometer.Evaporations from water surface and bare soil are compared.The results shows that the water depth is 10 cm above the soil surface,the transpiration rate presents a singlepeak curve pattern with the peak value occurring at around 14:00.While with the time progress,the transpiration rate decreases if Phragmites Australis is submerged in the water for a long time.When the water depth is below the soil surface,the transpiration rate will show a double peak pattern.The diurnal variation of transpiration exhibits a noon break phenomena at noon time (12:00) due to stoma closing.The water depth has a complicate influence on the ratio of evaporation and evapotranspiration.When the groundwater depth is about -20 to -40 cm,the ratio would be the smallest.The evapotranspiration is enhanced when the Phragmites Australis is planted in the wetland.The ratio of evapotranspiration from the open water surface with Phragmites Australis and evaporation of that without Phragmites Australis is about 2.When the water depth is below the soil surface,the ratio of evapotranspiration from the land with Phragmites Australis and from the bare soil will be in the range of 3 to 3.5.The daily evapotranspiration from the Phragmites Australis wetland varies significantly due to changing meteorological conditions.The Phragmites Australis evapotranspiration can be well correlated to climatic factors,such as the daily average of photosynthetic active radiation,the daily average air temperature and daily average relative humidity.The corresponding correlation equation can be established.The evapotranspiration from the Phragmites Australis wetland can be calculated using the equation when the observation is not available.
Abstract: 720 soil samples were collected at eight sites together with 7 populus euphratica Oliv samples obtained from a 6.8524 hm2 sized natural forest.The object of this study is to investigate the spatial variation and effects of moisture and salt content in soil on populus euphratica Oliv in the middle and lower reaches of the Shule River in Hexi Corridor,Western China.The samples are analyzed using statistical and contiguous quadrat methods.The results show that the soil moisture content is increased with the depth while the soil salinity content is decreased with the depth.Significant moisture and salt variations are found at soil depth 0-80 cm.Less variation is observed at the deeper soil.The soil moisture content is the lowest at the surface,while the opposite is true for salinity.There is a decrease in soil moisture and an increase in salinity in the downstream direction from the middle reach to the lower reach of the Shule River.The growth of populus euphratica plants is found to be deteriorating in the forest.Tree population structures are incomplete,sparse tree stands,and dwarfism and declining in the lower reaches of the Shule River.In this way,the populus euphratica forest in the lower reaches of the Shule River will die out in the near future because of rapidly declining.
Abstract: Streambed structures are developed in many mountain incised rivers as a result of fluvial morphology.They affect the further morphological process in some aspects such as channel stability enhancement.In order to study the role of the structures in morphological evolution in incised river channels,the landform features and structures were investigated and analyzed in the typical incised rivers.The results show that landslides and avalanches would likely occur due to earthquakes or rainstorms when the valleys are deeply incised and the valley slopes exceed a critical value.Thus,the river evolution will enter to a new phase of fluvial geomorphology after incision widening.A large amount of substances enters into channels enhance the intensity of streambed structures,and sustain higher gradients and form river knickpoints.This reflects the river system's selfadjustment,and in turn,reveals the existence of a negative feedback mechanism that is "incisionlandslides structures developmentincision impededequilibrium".The mechanism can lead the incised river system into the state of equilibrium,in case of invariable input conditions.
Abstract: A highperformance Godunovtype finite volume scheme is proposed for numerical simulation of dambreak flow over highly irregular terrain with complex geometries.The scheme is used to solve the twodimensional shallow water equations on triangular grids.Using the variable reconstruction and limiter techniques,the numerical flux can be calculated with the HLLC (HartenLaxvan LeerContact) solver.The Hancock predictorcorrector method is adopted for time stepping.The bed elevation is assigned to the vertices of grids,which is beneficial to wet/dry fronts treatments.The flux correction terms combined with the central approximation for the central bed slope source term can preserve a wellbalanced property.The stiff problem due to the friction term is investigated,and a semiimplicit scheme is proposed to treat the issue.Numerical results from test examples show that the new scheme is stable,robust,and wellbalanced,thus having a wide range of application prospects.
Abstract: The study of hydrodynamics in the surf and swash zone is essential to understanding the nearshore sediment transport and coast beach evolution.A numerical model is developed to analyze the flow mechanism in surf and swash zone under the influence of submerged breakwater.The twodimensional Reynolds Averaged NavierStokes equations,together with a nonlinear κ-ε turbulence model,and a finite difference method are employed in the model development.For a better simulation of wave breaking,a piecewise linear interface construction volume of fluid technique is utilized,which has good accuracy in describing air/water surfaces.The numerical model is validated with the experimental data and used to analyze the influence of submerged breakwater.The numerical results indicate that the location of breaking point and hydrodynamic characteristics in surf and swash zone are changed by the submerged breakwater.The wave height (H),wave length (L),depth of submergence (R) and crest width (B) play an important role in influencing hydrodynamic processes in these two zones.Under the same incident wave,the maximum turbulent kinetic energy and turbulence dissipation rates in two zones decrease as B/R increases.The dimensionless numbers of Re,Fr and St are deduced form RANS equations and used to describe hydrodynamics in surf and swash zones.The wave breaking could take place near the shore as RL/BH increases,meanwhile Re and Fr increases,and at the same time St decreases.
Abstract: A threedimensional (3D) numerical model for nearshore waveinduced currents is established,in which the phaseaveraged 3D residual momentum flux,surface roller and wave turbulence are introduced as driving forces,and the wavecurrent combined bottom shear stress is taken into account.An energy balance equation of the surface roller is derived,considering the bottom slope,energy transmission rate and roller density.The LarsonKraus formula for the 2D wave turbulent mixing coefficient is extended to its 3D form.A number of experimental cases are used to validate the model,including the wave setup/setdown (1D),undertow (2-DV),longshore current (Q3-D),rip current (2-DH) and the circulation behind a detached breakwater (2-DH).The validation results show that the model is able to effectively describe the waveinduced current phenomena of various dimensions,and the incorporation of the surface roller is mandatory.The uniformity of the longshore current speed profile in the surfzone is related to the vertical turbulent mixing in the effect of waves.
Abstract: Based on the unstructured meshes and uses finite volume method,an adjoint model of data assimilation is established to study the variation of Bottom Friction Coefficients (BFCs) in tidal bore affected estuaries and to inversely estimate the spatial and temporal variation of BFCs during flood or ebb tide.A series of twin experiments on the BFCs were carried out in a generalized estuary.The experiment indicates that the existence of large spatial variation in BFCs will have a negative effect on the inversed result.The result can be improved with the increase in assimilated observations.The adjoint model is tested using the observed data in the Qiantang Estuary.The derived BFCs during the flood and ebb tide are 0.000149 and 0.001520 (equivalent to 0.012206 and 0.038987 of Manning coefficients),respectively.Both deformation of tidal waves and occurrence of tide bores are successfully simulated using the inversed values of BFCs.The result reconfirms the previous findings that the BFCs during the flood are smaller than that during the ebb in the Qiantang Estuary.
Abstract: Extracting urban features from dense building is essential to the simulation of urban flooding using classical twodimensional models.These urban complex structures are parts of boundaries in the simulation domain,where the mesh may be locally refined.As a result,the largescale urban flood simulation may not be feasible due to limited information in urban buildings.In this study,the classical twodimension shallow water equation is improved through the introduction of a plot ratio coefficient that can represent the building influence on urban flood simulation.The modified two dimension shallow water equation is solved by a finite volume method with artificial upstream flux vector splitting.The improved model is tested in two numerical case studies.The result shows that the model is able to simulate urban floods with an acceptable accuracy.At the same time,the requirement for urban feature extractions is significantly reduced.
Abstract: As a consequence of the dam,the physical transport of dissolved matter is profoundly affected by human activities in reservoirs.A threedimensional numerical model,Environmental Fluid Dynamics Computer Code (EFDC),is used to study the physical mechanisms of mass transport in the Falls Lake Reservoir in North Carolina,USA.The spatial and temporal variations of the mean age and the residence time of a tracer are analyzed.Under steadystate conditions with constant in/outflows,the dissolved matter transport is dominated by river discharges.Under dynamic conditions,the phase of the water storage is also an important factor.The geometric feature and the function of the reservoir and the distribution of the tributary runoffs are the major factors that contribute to the differences of the local residence times.
Abstract: The variation in operating stages could result in a change of water temperature structure of multiyear regulating storage reservoirs.Thus,understanding of the water temperature dynamics would be essential to study the effect on the downstream water temperature.Using the observational data from the Longyangxia reservoir for the period 1988 to 2008,the variation in reservoir temperature profile and the effect of reservoir operation on the downstream water temperature are studied.The data includes operating stages and reservoir and downstream water temperatures.The result shows the variation in reservoir temperature profile and the effect of reservoir operation on the downstream water temperature is closely related to the reservoir operating scheme.From December to next March,the reservoir water temperature is either weakly stratified or uniformly distributed; higher stages can store more heat,and both reservoir water temperature and downstream water temperature change synchronously with reservoir stages.From May to October,the reservoir water structure is stratified; the stratification is mainly controlled by the reservoir stage,and the downstream water temperature is reversely related to reservoir stages.In the months of November and April,the reservoir temperature structure is rather uniform,and serves as turning points.This study provides valuable information for the determination of the temperature dynamics in large reservoirs and its influence on downstream water temperature.
Abstract: The global climate is warming significantly over the past 100 years,temperatures in the future will rise,and the patterns of precipitation will be altered.Based on a comprehensive literature review,this study summarizes the research status of wetland ecohydrology from three aspects:The impacts of climate change on wetland hydrology and water resources,the interaction of wetland hydrology and ecology under the influences of climate change and wetland ecohydrological models.Over a long period,wetland ecohydrology only focuses on the ecohydrological process,however,it has been moving to the direction of an interdisciplinary science integrating interactions of climate,ecology,and hydrology.At present,studies on the interaction between wetland hydrology and ecology is mainly focused on the oneway coupling analysis,e.g.,the impact of hydrological processes on vegetation.It has been a lack of researches on the interaction mechanism between the wetland hydrological process and the ecological process under the influence of changing climate.The impact of climate change on wetland ecohydrology has become a scientific issue,and deserving a quick action from the hydrological research community.The physicallybased modeling approach is expected to be the most important tool in predicting the wetland ecohydrological response to the future climate change.
Abstract: We put forward a risk definition of groundwater systems on the bases of summarizing previous studies in groundwater risk analysis.Characteristics of groundwater systems are reviewed in detail,and risk effect factors in a groundwater system are analyzed and highlighted.The risk factors are then resumptively classified into three categories:Uncertainty of natural phenomena,social uncertainty and limitations in human cognition.Discussions on risk analysis methods are also given.For the issues and deficiencies on the subject,we highlight four aspects to improve the risk analysis of groundwater systems.These aspects include developing basic theories and expanding research methods,properly selecting the risk analysis approaches to addressing different concerns,combining risk probability and its loss,and studying on risk of risk analysis.