Abstract:The SWAT model and RegCM3 regional climate model were used to predict the future trend in change of the runoff in the source region of the Yellow River under an A1B scenario. The SWAT model for the source region of the Yellow River was constructed, and it was calibrated and verified with hydrometeorological data, including daily temperature, precipitation, and discharge, from 2000 to 2005 and from 2006 to 2008, respectively. The Nash-Suttcliffe efficiency coefficient was 0. 86 in the calibration period and 0. 89 in the verification period, and the correlation coefficient was 0. 83 in the calibration period and 0. 86 in the verification period, indicating that the model’s simulation effect was good. The RegCM3 regional climate model’s capability of simulating the surface air temperature and the precipitation in the source region of the Yellow River was evaluated, and the simulation results, which agreed with observations, were satisfactory. The climate data of the source region of the Yellow River under the A1B scenario predicted by the RegCM3 regional climate model were processed by the system through correction and interpolation, and then applied to the SWAT model to simulate the runoff series of the source region of the Yellow River from 2010 to 2098 and predict the change trend of runoff in the future. The results show that runoff at the Tangnaihai Station in the source region of the Yellow River will decrease continuously from 2010 to 2098 in general; it will decrease from 2010 to 2039, will increase from 2040 to 2069, and will decrease from 2070 to 2098; during the periods from 2010 to 2039 and from 2040 to 2069, it will change insignificantly; and during the period from 2070 to 2098, it will have a significantly decreasing trend.

Abstract:Based on data from 53 rain gauge stations, ten runoff stations, and four meteorological stations in the Laohahe Basin, a typical semi-arid area in northern China, we studied the temporal and spatial variations of key hydrological factors in ten sub-basins of the Laohahe Basin over the past 50 years. We employed the rank-based Mann-Kendall trend test and Pettitt change-point test to analyze the change trends and significance levels of precipitation and runoff in the basin and calculate the change point. Then, we adopted a semi-distributed variable infiltration capacity(VIC)model to simulate the rainfall-runoff processes of the ten sub-basins during the baseline period. Based on calibrated parameters of the model, we reconstructed natural runoff during the variation period, so as to quantitatively separate the effects of climate change and human activities on the abrupt reduction of the runoff in the basin. The results show that since 1980, 90% of the runoff reduction in the basin has been caused by human activities, and 10% of the runoff reduction has been caused by climate change. In terms of human activities, widespread agricultural irrigation especially in the middle and lower reaches, was the essential reason for the abrupt reduction of runoff in the Laohahe Basin. Furthermore, the impact of human activities on runoff reduction varied with dryness and wetness changes across the basin, with greater impact in dry years than in wet years.

Abstract:As floods often occur in steep terrain and water flow changes rapidly, the calculated values in two-dimensional numerical simulations of flash flood disasters are unstable and even the calculation diverges in the simulation. To solve these problems, we present a grid outflow correction method, which is based on the leap-frog finite difference format. Through circular modification of the outflow rate of the grid, this method ensures mass conservation over the whole process of computation and improves the stability of numerical calculation. While using the local dam bursting model, we conducted mass conservation comparison between the simulated result of the grid outflow correction method and that of the algorithm of the implicit alternating direction. The results show that the grid outflow correction method can ensure simulation accuracy and numerical stability under the conditions of steep terrain and a moving boundary. Based on the proposed method, simulation of the process of the extreme flash flood disaster that occurred in 2010 in Zhouqu County, in Gansu Province was carried out. The comparison of simulation results and the results of remote sensing estimation after the disaster shows that the deviation of the flood evolution time, speed, and impact height were within ±5%, and the evolution path was consistent.

Abstract:In order to improve the precision of the simulation of small and medium-scale floods when using traditional methods, we used a method of doing hydrology backwards to simulate the flow at the outlet cross-section of the study area. Based on the characteristics of slowly-varying low flow in the study basin, we deduced the relationship between the average runoff of a period and the changing rate of the average runoff using the water balance equation, established an equation for the simulation of small and medium-scale floods based on doing hydrology backwards, and deduced the application range of the equation. The simulation of floods over the Qingjiang River Basin during the period from 1989 to 1995 showed that the simulated rising and recession trends agreed with observed data, the recession curves were better fitted than the rising curves, and the precision of the simulation of flood peaks met the requirements. Compared with traditional flood simulation methods and low-flow forecasting methods, the proposed method can be easily used for calculation and can describe the magnitude of peak flows of small and medium-scale floods using flood hydrographs, providing a scientific decision-making basis for reservoir operation.

Abstract:Five-dimensional characteristics of a natural-social dualistic water cycle system were analyzed. The entropy theory and the synergetic theory were used to evaluate and compare the multidimensional regulation scenarios of the water cycle system. Dominant factors(order parameters)of multi-attributes were regarded as the evaluation indices for the regulation scenarios. A quantitative relationship between the evaluation indices and the five-dimensional characteristics of the water cycle system was established. The evaluation indices of system coordination degree and integrated distances of order degree were established for regulation alternatives in order to quantitatively evaluate the effects of multidimensional regulation and to determine the optimal scenario. The feasibility of the proposed methods for scenario evaluation and optimal selection for multidimensional regulation of the water cycle system were verified through a case study in the Haihe Basin.

Abstract:Three typical real-time correction methods, including the traditional error autoregressive method, the nonparametric correction method based on the K-nearest neighbor(KNN), and the multi-cross section correction method based on Kalman filtering, as well as a combination of the KNN method and the Kalman filtering method were used in combination with a one-dimensional hydrodynamic model for flood forecasting and real-time correction in the Wujiadu-Xiaoliuxiang reach of the Huaihe Basin. The principles and construction methods of the four methods are briefly introduced, and a comparative analysis of their simulation results, especially of the stability of the flood peak, the time of occurrence of the flood peak, and the error of occurrence of the flood peak, is conducted. The conclusions are as follows: the three basic methods can improve the accuracy of flood forecasting over quite a long forecast period, and the combination method is more effective and reliable for flood peak simulation, and is more applicable to forecast correction.

Abstract:At present, few studies have been conducted on turbulence characteristics of stratified flow in braided rivers. In this study, a physical model experiment was carried out to study the variation of the turbulent intensity of thermally stratified shear flow with different velocity ratios of two layers and width ratios of two anabranches. The results show that, as the velocity ratio decreased, the stratified flow in the braided river changed from stratified flow to neutrally stratified flow. As to the neutrally stratified flow, the sectional high-turbulence zone along the anabranches changed from a C-type distribution to an inverse C-type distribution, and the turbulent intensity was mixed well throughout the section in the end. With the increase of the channel width, the section of the high-turbulence zone appeared later, and the quantity of the turbulent intensity increased. Under other conditions of stratified flow, the range and quantity of high turbulent intensity all changed. At the confluence section, the flow in the center of the section was mixed violently in the symmetric braided river. With the increase of the velocity ratio, the quantity of the turbulent intensity decreased. The high turbulent intensity zone moved to the narrowed left anabranch in the non-symmetric braided river, which was associated with the tail position of the mid-bar.

Abstract:Field exploration, sampling, laboratory tests, and numerical simulations were conducted to study the impacts of the spatial variability of hydraulic conductivity of the bottom stratum of a reservoir on solute transport in groundwater. A case study was carried out in the Beidagang Reservoir, in Tianjin City. The results are as follows: the hydraulic conductivity of the bottom stratum of the Beidagang Reservoir was at a low level and showed a large spatial variability; the flow flux in the groundwater increased with the hydraulic conductivity and the impact of the average value of the hydraulic conductivity on the flow flux was greater than the standard deviation; inhibited by the groundwater flow, the solute transport weakened when the average value of the hydraulic conductivity increased; and the solute transport intensified when the spatial variability of the hydraulic conductivity increased because of relatively weaker groundwater flow.

Abstract:Based on monitoring results from eight monitoring sections in Tongli Town from March to August in 2012, an improved fuzzy comprehensive evaluation method was used to evaluate the water quality in this town. Six membership functions and entropy weight were used in this method, and ultimate water quality classification was judged by the effective degree of the maximum membership degree principle and the confidence criteria. The improved fuzzy comprehensive evaluation method was compared with the traditional fuzzy comprehensive evaluation method. The results show that the internal water quality of the town reached grade Ⅴ or a point inferior to grade Ⅴ, and the external water quality was better than the internal one. Compared with the traditional method, the improved method shows better performance in distinguishing different grades of water quality and can be used to evaluate water quality inferior to grade V, it has a simple weight calculation and can determine the main pollution factors, and the evaluation results are more reasonable and reliable.

Abstract:In order to achieve a better control effect, the fractional-order was used to describe the damping force, which was supposed to be an α-order derivative of the displacement vector, and a variational-order controller design method was developed. The detailed process is as follows: First, it is assumed that the damping force in the original equation of motion is a β-order derivative of the displacement vector and the controller is designed according to this assumption. Second, considering the equation of motion that includes an α-order derivative as the control object, a control strategy based on systemic output is applied to ensure that the designed controller can be used for the original model. Third, the optimal parameter β is determined with the search method according to the third generation of the benchmark building control performance index. In this study, there was a damping effect when the fractional-order ranged from 0 to 2, and the search scope was between 0 to 2. The simulation results show that optimal parameters can be found to obtain a better control effect when β is different from α. Meanwhile, the selection of the optimal β varied with different performance indices. Finally, a simulation example verified the feasibility of the proposed control strategy.

Abstract:In order to overcome the shortcomings of the ionospheric total electron content rate(TECR)and dual-frequency code phase combination(MW)methods, a combination of the two methods was used for cycle slip detection. First, the TECR method was used to detect the cycle slip. Then, the MW method was used to detect the cycle slip for the second time. Finally, the ionospheric TECR and the wide lane ambiguity of MW were used together to detect the cycle slip on L₁ and L₂ frequencies. This combined method was not affected by the geometrical distance between the receiver and satellite, the receiver clock offset, the satellite clock offset, and ionospheric refraction. According to the test results of measured data, the TECR and MW combined method is more effective and reliable than a single method in detecting GPS cycle slip.

Abstract:To guarantee stable operation and power quality in the turbine units of a hydropower station, an exact mathematical model was built for a long-distance water diversion-type hydropower station with parallel surge chambers. The dynamic characteristics of the hydro-mechanical system were comprehensively simulated, and stability analysis of small fluctuations in the system was conducted. Based on the rigid model and elastic model for the pipe flow, analysis models were established to describe the dynamic characteristics of the hydro-mechanical system. Combined with numerical analysis of both frequency and the time domain, the effects of different layouts of the water diversion system and elastic models with different orders for the pipe flow on the system’s stability analysis were investigated. An example shows that, instead of the commonly used rigid model, which has application limitations, a three-order or higher-order elastic model should be used for the pipe flow at the long-distance water diversion-type hydropower station to fully demonstrate the system’s vibration characteristics and stability performance.

Abstract:Based on the flow characteristics of an actual water-blocking hydraulic structure, the internal boundary method, the equivalent discharge roughness correction method, and the equivalent discharge topographic correction method were used to correct the discharge capacity, in order to fit the simulated discharge capacity with the actual discharge. Simulation of water level and flow velocity was conducted under the conditions of steady flow and unsteady flow in a two-dimensional hydrodynamic numerical flume model to compare the three methods. The results show that the former two methods can accurately reflect the discharge and the properties of the flow around the water-blocking hydraulic structure, and the water level and flow velocity simulated by the third method, due to the local topographic change, excessively deviated from the actual values.

Abstract:In order to scientifically and objectively evaluate the level of modernization of water conservancy development in northern Jiangsu Province, on the basis of the index system of water conservancy modernization of Jiangsu Province, the TOPSIS method based on the weight of the variation coefficient was used to calculate the weights of current evaluation indices. In comprehensive consideration of the weights of the current evaluation indices and the evaluation indices of water conservancy modernization of Jiangsu Province, the indices were weighted again, in order to comprehensively evaluate the water conservancy modernization of six typical counties in northern Jiangsu Province and to verify the rationality of the method. The study results show that the index system with new weights thoroughly reflects the characteristics of northern Jiangsu Province and meets the region’s development requirements, and it is closely related with the present situation of water conservancy development in northern Jiangsu Province, providing guidance for the water conservancy modernization in this region.

Abstract:In this study, we developed a river network model based on the complex network theory. Taking the Haihe River system as an example, we constructed two river network models, Model Ⅰ and Model Ⅱ. Model Ⅰ included natural vertices and Model Ⅱ included both natural vertices and artificial vertices. Based on the properties of the vertices and edges in river networks, we propose the vertex weight index and edge weight index to assess the vertex importance and edge importance, respectively, and analyze and compare the vertex importance and edge importance of the Haihe River Network. Finally, we summarize the key parameters of the proposed river network model and discuss the future development of the model.

Abstract:In order to solve the non-minimum phase problem that arises from the nonlinear control method of state-feedback linearization, a nonlinear controller was designed to control the non-minimum phase effectively. First, through a differential homeomorphism transformation, the original nonlinear systems were transformed into a linearization canonical form, which was composed of the external dynamics described by a linear sub-system and the internal dynamics(namely zero dynamics)described by a nonlinear sub-system. Then, a nonlinear controller design method was developed for the non-minimum phase system, in which zero dynamics were unstable, based on pole assignment and Lyapunov stability theory. Numerical simulations show that, not only can the controller designed by the developed method meet the performance requirements of external dynamics, it can also guarantee the stability of zero dynamics.