Abstract: Continuous channel degradation has occurred recently in the Lower Yellow River(LYR)due to water impoundment of the Xiaolangdi reservoir. In this paper,the observed hydrological data from 1999 to 2005 are used to analyze the processes and characteristics of the recent channel adjustment in the LYR. The main research results can be described as follows. The scour amount in the braided reach makes up 77% of the total one in the LYR,and the scour magnitude per unit channel length in the braided reach upstream of Gaocun is relatively large,while the value in the reach between Gaocun and Sunkou is lowest among all the lower reaches. The cross-sectional profiles adjustment in the lower reaches is characterized by the channel narrowing Since 1855 the longitudinal main channel profiles in the LYR are concave-shape curves,and concavity values of these profiles increased slightly with the recent channel degradation. The migration amplitude of the thalweg in the braided reach is greater than that in the meandering reach. The bankfull discharges in the lower reaches increases due to the scouring in the main channel Due to the obvious armoring of bed material,the longitudinal coefficients of channel stability increases slightly in the different reaches. The lateral channel stability almost does not change in the braided reach,and increases slightly in the transitional or meandering reach.
Abstract: In this paper,a model based on the generalized curvilinear coordinate is presented to simulate 2D horizontal flow and sediment from Yichang to Yangjianao reach at the downstream of Gezhouba hydropower station. The governing equations of the model are discretized by the finite volume method. The data of flow and sediment from 2002 to 2004 are adopted to verify the accuracy of the model. The change trend in the deposition and erosion for this reach from 2005 to 2014 is forcasted after the running of the Three Gorges Project. There is the possible change trend in water level at Yichang station and the important shallow reach slope after scouring of Yichang hydropower station in the downstream. Thus the prediction results can provide scientific basis for the research of the river regulation countermeasure and measures.
Abstract: The trends in the water and sediment loads of the main rivers in China are analyzed with the data till 2006 from the series publication of China Gazette of River Sedimentation by using the water-sediment diagram. According to the trends in their annual runoff and sediment load entering to the sea main rivers in China can be classified into 4 groups:(1)rivers with stable water but decreased sediment loads,including Huaihe river and the rivers to its south;(2)rivers with decreased water and sediment loads,including Liaohe and the Yellow Rivers;(3)river with slightly synchronal decreased water and sediment loads,including Songhua river;and(4)rivers with greatly reduced water and zero sediment loads with example of Yongding river Most riverste the south of the Huaihe show no evident trend in their annual runoff,but dramatically decrease for their sediment load. Both water and sediment loads of rivers north of Huaihe river have the evident decreasing tendency. The recent 10 years the average values are only 1/3 of the long term average values for the Yellow River's runoff and 1/4 for its sediment load,and the water and sediment loads approach zero for the rivers in Haihe river system In general,the sediment loads of most rivers in China decrease evidently. The drops in the water and sediment loads of the rivers are mainly caused by human activities. The reduced sediment loads of the rivers in south China are more closely related to the reservoir construction,sand mining and soil conservation activities. The decreasing water and sediment loads of rivers in north China are mainly the results of rapid increased water consumption,reservoirs and their operation modes,and effects of water and soil conservation measures. It also shows that it has advantages using water sediment diagram in analyzing the trends in water and sediment loads of rivers.
Abstract: Traditional reservoir operation is mainly designed for water supply and/or flood control,and the purpose of the ecological reservoir reoperation is to achieve the ecological and environmental objectives:water quality,ecosystem,sediment and disease control etc. We propose an ecological reservoir reoperation model based-on ecological flow regime. The model takes the maximum of reservoir benefit,such as annual power generation as the objective subject of the ecological scenarios. The ecological reservoir reoperation model is applied in a tributary in the Yellow River basin as an example.Based on the status quo of the watershed,four ecological and environmental objectives are given and five ecological scenarios are proposed. The results of the model indicate that the annual power generation only decreases by 7.6% with all the four objectives met than the non-ecological objective. According to the results,the hydropower benefit of the reservoir will not decrease dramatically while the ecological demand can be met,if we introduce a suitable reoperation pattern.
Abstract: The stochastic simulation has become an important method for studying the solute transport in heterogeneous aquifer. In this study,a Monte Carlo method is used to study solute transport in a multiple-scale heterogeneous aquifer. The aquifer is composed of two materials and hydraulic conductivity distribution within each material is heterogeneous. The hydraulic conductivity field within each material is assumed to be statistically stationary,while the conductivity field in the whole aquifer is nonstationary. Since Monte Carlo models relies on the stationary parameter field,the separate stationary conductivity fields are generated on the two materials and then combined by using two methods,one of which is proved more proper taking the model's accuracy and efficiency into account.
Abstract: On the basis of the field investigation of ammonia nitrogen contaminated by landfills in the Tianjin shallow groundwater,two representative water bearing media were sampled in the Tianjin coastal plain,and their and colloid's major physico-chemical properties were analyzed respectively. The dynamic curves and isotherms of ammonia nitrogen adsorption on the colloid of water bearing media were measured and the influence of particle size,zeta(ζ)potential and electrophoretic mobility on the adsorption were evaluated. The research results show that the kinetics of ammonia nitrogen adsorption on the colloid is the logarithmic curve,and the equilibrium period of the adsorption lasts for 20-24 hours,and all the adsorption isotherms are straight. In addition,It is found the colloids release out the ammonia nitrogen rather than adsorb the aqueous ammonia nitrogen when the ammonia nitrogen content is lower than a certain value. The smaller colloid particle is,the stronger the adsorptive capacity of ammonium ion on colloid. With increasing of the zeta(ζ)potential and electrophoretic mobility of colloid particle surface,the adsorptive capacity of ammonium ion on colloid goes up.
Abstract: A coupled bio-physical model is used to simulate the seasonal variation of primary production,chlorophyll a,nitrogen and phosphorus in the Bohai sea,and the modeled results agree with the observations reasonably. Based on the validated simulations,the impact of two external nutrient sources on the Bohai ecosystem is further examined. It is found that the influence of river-borne nutrients mainly concentrate on estuaries,whereas the reduction of sediment-borne nutrients may seriously inhibit the onset of algaelbloom in the whole Bohai sea.
Abstract: Based on the monthly climate records of Yuanmou,Binchan,Dongchuan,Xiangyun,Chuxiong,and Kunming stations in the period 1960-2000,as well as crop pattern and cultivate data in 2000,the Mann-Kendall trend and the Rescaled Range Analysis(abbr.R/S)method are adopted to research the tendency in aridity-humidity and irrigation water requirements in Jinshajiang dryarid valley in the last 40 years. The results show that the precipitation and the temperature decrease,and sunshine hours increase in the valley. But the temperature increases in the branch upstream of Longchuanjiang,Yupaojiang, Puduhe,etc,thus,results in ET0 decreases remarkable in Jinshajiang basin. Furthermore,the aridity-humidity index,paddy irrigation quota and total agriculture irrigation quota also decreases. The turn point of climate factors,ET0,aridity-humidity index,paddy irrigation quota and total agriculture irrigation quota in Jinshajiang valley are focused the late 1970s-1980s and the late 1980s the early 1990s,and Binchuan station which occurs minimum precipitation is most sensitivity to climates change.
Abstract: Migration of solid and liquid water in black soil as well as soil temperature are studied with the method of Neutron Probe TDR during the soil freezing thawing-process. The results shows that the soil water content in the upper-layer increases 73.7 mm that accountes for 13.4% of annul rainfall,as a result of vertical water transportation from downside soil profile of 2 m depth in the freezing period. The content of solid water is driven by the soil temperature and content and the total water content arrives at a peak of 60% of total water during late February and early March. The content of liquid water decreases in the process,in which the lowest amount accounted for 40% of total water in the steady freezing process.
Abstract: Based on the summarization of research on total dissolved gas(TDG)supersaturation,field observation of TDG downstream of Zipingpu dam was taken. The dissolved gas saturation levels were measured and recorded along transects distributing in 40 kilometers downstream of the Zipingpu dam. It shows that the depth and sand concentration of the river is an important factor affecting the desorption of TDG downstream of high dam. It provide a basis to find out the rule of desorption of dissolved gas supersaturation downstream of high dam,which is important for protecting fish in downstream of high dam.
Abstract: Based on the thought of hydraulic radius separated method,a new computation formula for open-channel resistance segment is created. The influence on flow resistance of flexible vegetation,which is submerged on bed surface of the open channel,is explored and analyzed. A three-dimensional-acoustic Doppler velocimeter is used to measure the velocity near the wall. Measurement of velocity in indirect method is used to determine the tangential stress on the wall. The hair of palm is used to imitate the vegetation. Under the condition of different heights and densities,a series of flume experiments are carried out. The vegetation roughness is used to express the vegetation resistance and the vegetation height and density is used to express the roughness of bed surface. By the regression analysis to experimental dates,the conclusion is that the vegetation roughness increases along with the increase of the vegetation height and density;the bigger the roughness of the vegetation,the more approximate to the vegetation height its numerical value. Empirical relationships between them are fitted and then the computation formula of vegetation resistance is derived.
Abstract: The experiments with various combinations of water discharge and spacing of artificial roughness elements are conducted to study the resistance characteristics of shallow open channel flows. The results show that(1)flow resistance is affected by the presence of artificial roughness elements with an significantly large increase at low discharges and relatively small at high discharges;(2)the spacing of the artificial roughness elements plays an appreciable role in enhancing flow resistance; (3)as the relative roughness size increases,the resistance coefficient increases following a relationship independent of flow discharge;and(4)uniform flow velocity distribution prevails at the water surface.
Abstract: The optimal Manning roughness coefficients(n)control system of two-dimensional shallow water equations are first derived by using the optimal control theory for the partial differential equations. Then,the algorithm for automatically calibrating distributed n is implemented based on the framework of the unstructured finite volume methods. Considering the operational application,the n is not defined in each cell,but in each land cover block. Two conditions are investigated in our calibration experiments. One is the time-independent n identification for steady flows,and the other is the time-dependent n, which has fixed reference value and varies with water depth as given empiric relationship for unsteady flows. In both groups experiments,it is found that the n can be successfully calibrated using enough observations. Also,the functional relationship between referencen and water depth can be identified. But,the iteration number for the identification of the functional relationship increases largely because of larger freedom of control variables. Finally,the strategy for calibration are suggested in the modeling flood event,in which varied n is required to be considered.
Abstract: of water level in this paper. Including seepage in a 3-dimensional theoretical analysis,the study first shows how the critical slope or angle of repose of sediment is related to the hydraulic gradient of seepage. The measured laboratory data rea-sonably fit well with the theoretical relationship in the case of injection and suction. The data reveal that the slope is reduced and increased with injection and suction,respectively. Additionally,the critical stable slope is shown to be related to both the hydraulic gradient and the seepage direction. The study identifies the seepage direction which results in a minimum critical stable slope for a certain hydraulic gradient of seepage.
Abstract: The paper gives the detailed instruction on the data acquirement of the valid cells of Acoustic Doppler Current Profiler(ADCP)near bed1 According to the analysis of the vertical distribution of the signal amplitude with the extremum theorem,the location of the bed is fixed and the velocity data are extracted which was once lost due to the disadvantage of ADCP software and the errors of the bottom track algorithm. The validity of the extracted data is verified by using the synchronous data with the same depth of electric current meter. The data acquirement of valid cells of ADCP near bed provides a kind of convenient and effective measurement of the velocity near bed and enriches the vertical velocity data,too.
Abstract: Human activities have great influence on runoff temporal change. The detected distinct transition point and relevant selected "unaffected" hydrological series that have great significance to assessment of soil and water conservation benefits. Taking Yanhe as an example,the distinct transition point of flood season runoff time series by the impacts of human activities has been detected by way of mathematical statistics analysis. And meanwhile,based on the datum before distinct transition point, the forecast model is set up only with the data series before the distinct transition point. The difference between the value derived from the equation and the observed value is right the influence on flood season runoff induced by human activities. Different from traditional methods,using hydrological datum and the synthesis coefficient of precipitation and runoff of flood season instead of annual ones,which could rationally weaken the impact of characteristics on rainfall and runoff in Loess Plateau. The analysis shows that 1970 is the transition point of runoff time series by impacts of human activities from the end of 1950s to 1980s,and human activities have affected significantly on hydrology of Yanhe basin since 1970.And in the year of 1981,human influence on river runoff reached maximum,with its value being 72.04%. In the 1970s and 1980s,flood season runoff was confined to reduced state at all times. So human factors is the primary one for the evolvement of Yanhe runoff.
Abstract: This study is conducted in the second forest of Chi-Lan village and Yu-Lan tea garden of Ta-Tung country in Yi-Lan. We measured the latent evapotraspiration by evaporation disc method at the two study sites and tried to understand the difference of the evapotranspiration on the different land use type. We hope the results of this study can afford the reference for the concerned authorities and the land developer. The study results show that the latent evapotranspiration over the garden ecosystem is clearly higher than that in the second forest ecosystem. We think the reason is that the garden ecosystem is an open system and the whole open system is exposed to the sunshine so it can accept sufficient solar radiance and resultsd in the higher latent evapotranspiration. While the situation in the second forest ecosystem is quite different because the plants in it have different heights and cover each other,which results in receiving less solar radiance. Furthermore,there are many deep-root plants in the second forest ecosystem so the characteristics of soil and water conservation are relative better than the garden systems. The results also suggest that the loss of the water content in per hectare land will increase 100～150 tons when the second forest ecosystem is developed as the garden ecosystem in winter.
Abstract: In this thesis,a new idea for estimating the periodicities of hydrological time series is put forward. Two new methods,series simulating and prolonging method(SSAP)and main frequency series reconstructing method(MFSR),are developed. The former is to build a suitable model to prolong the length of the original series,and the latter is to reconstruct the main frequency series of the original series. Maximum Entropy Spectral Analysis(MESA)is used to analyze the periods of new series. Various period-estimating methods(including traditional ones and newly developed ones)are used to identify which is better for same time series. Results show that the traditional methods(Fast Fourier Transform,MESA and Wavelet Analysis) are not as good as expected because of the influences of short length of series,complex random series and skew distribution, etc. However,using new methods(SSAP,MFSR)are not so strongly affected. It can be concluded that the new methods would greatly improve the estimation of results and,to some extent,eliminate disturbance.
Abstract: As water freezes into ice and ice melts into water,evident difference will come into existence in its physical parameters such as resistance,capacitance and temperature between ice,measured air above ice layer measured and water below ice layer. According to the aforementioned features and basing a new the oretical framework of measurement on ice-thickness and beneath-ice-surface water levels by distinguishing the physical characteristics of air,ice and water,the paper analyzes the laws of the resistance and capacitance of ice with conductive impurity,mixture of ice and water,water and air change as temperature changes,draws conclusions such as ice as a weak conductor,monotonic feature of ice and water,and introduces the design of the structure of a new-type of ice-thickness sensor,its measurement method,and its application in practice.
Abstract: Misjudgements occurred when the general attribute recognition model based on linear measure function(LMF-ARM) is used to make assessment on the virtual samples drawn randomly from the criterion of water quality. This leads to the down-ward reliability of the result while LMF-ARM is applied to the actual water samples. Therefore,the improved attribute recognition model based on non-linear measure function(NLMF-ARM)is proposed here. The results given by the later model are much better than the former,according to the tests of the virtual samples selected by both the random method and the orthogonal design. It indicates that the measure function can play an important role during the process of utilizing attribute recognition model to make comprehensive assessment. So the conclusion can be draw from the case on a city groundwater quality assessment,that non-linear measure function,compared with the linear,has better abilities to describe the natural attribute degree of assessment indexes. Because of the higher reliability than LMF-ARM,NLMF-ARM has wider applicability in the comprehensive assessment of water quality.
Abstract: Based on the virtual displacement principle of finite element method,a weak variation of GAO-YONG turbulence equations is put forward. The subroutine of the element and the integrated finite element code are generated by the finite element program generator(FEPG)successfully. The numerical simulation about the lid-driven cavity flow is conducted. The vorticity contour in the cavity and the velocity changing curve of cavity's central lines are acquired and agrees with the established results very well. The Gao-ong turbulence equations able to gain real viscosity field in complex flow is proved. The engineering application foundation of the Gao-Yong turbulence equations is established.
Abstract: Classification helps us create order out of chaos and be usually used as a means of ordering observation and descriptions. The river classification phase occurs during the newly early stages of development of hydroecology. The purposes and approaches of river classification are simply introduced and the mainly four types of classification schemes,i.e. morphological,hydrological,ecological and value-based schemes,are reviewed and commented. The integration and systematization are the trends of the development in the classification schemes,and the special progresses are made by linking the single factors to the multiplex ones,the qualitative analysis to quatitative ones,the structural features to processes ones,the linear rivers to the large-scale hierachical systems and the natural systems to social ones,etc. With the development of the empirically based laws and finally to the theoretical understanding,and the improvement of the multidiscipline cooperation and data availability,the descriptive classification schemes will give way to the predictive ones.The preexistent experiences from other large countries with a great diversity of aquatic ecosystem are beneficial to the nationwide forthcoming watershed restoration and management in China.
Abstract: Univariate frequency analysis cannot provide a complete description of hydrologic variables with multicharac-teristics,and many hydrological frequency problems should be solved by the bivariate probability distribution model concerning the encounters and joint distributions of different hydrologic events. This article presents a review of various bivariate probability distribution models,and Copulas as a new bivariate probability distribution method are introduced. Advantages and limitations of each of these models are pointed out. Most of the present models are constructed based on the linear correlation of variables,and some of the models usually assume that the variables should have the same marginal distributions or have a strict restriction of correlation between variables. In reality,however,many hydrological events do not have the same type of marginal distributions,and various nonlinear dependence exists among variables. The copula method relaxes the restrictions of traditional bivariate probability models,and no assumption is needed for the variables to be independent or normal or have the same type of marginal distributions. The complex asymmetric and nonlinear correlation among variables can be described using copulas. As a flexible method to construct joint multivariate distribution,the Copula methodology is promising concerning hydrological frequency analysis.