Abstract:Although the Piecewise Muskingum method for river flood calculation has been widely used in China, the major limitation that hinders the further application of the Piecewise Muskingum method within distributed models still needs to be addressed. This method with empirical parameters cannot consider the impact of changing river cross-section characteristics and hydraulic roughness on the flood computation. In this study, the Muskingum-Cunge-Todini variable parameter method and the non-linear reservoir method, which could consider the channel cross-section geometry and hydraulic roughness, were used in the river flood calculation in the middle part of Huaihe river, from Wujiadu to Xiaoliuxiang, and the middle part of Hutuo River, from Huangbizhuang to Beizhongshan. In addition, the river flood calculation with the Piecewise Muskingum method also has been conducted as a comparison. Initial tests indicate that the Muskingum-Cunge-Todini variable parameter method and the non-linear reservoir method have high simulation accuracy in the studied cases. The correct rate of flood peak is above 86%, and the coefficient of certainty is greater than 0. 8. This study can provide references for the flood calculation considering the change of the channel cross section and hydraulic roughness characteristics.

Abstract:In order to obtain the characteristics of wind field and flow field as well as the influence of different types of wind fields on the flow field of Taihu Lake, 6 acoustic doppler current profilers(ADCP)and 4 meteorological stations were set up in different areas of Taihu Lake, and the synchronous data of flow field and wind field were obtained. The results show the floolwing: (a)The spatial distribution of wind field in Taihu Lake was not uniform, the wind speed varied greatly among 4 stations, and the difference of wind direction was expanded along with the decrease of wind speed. (b)The flow field in Taihu Lake had obvious characteristics of wind-generated flow. When the average wind speed was greater than 6. 7 m/s, there was a counterclockwise circulation that appeared in the western lake area, and there was no obvious flow stratification during this period. When the average wind speed was less than 3. 8 m/s, the circulation in the west fade away. However, the flow stratification was obviously developed, the current direction of each layer was relatively stable but different, and the compensation flow developed. (c)According to the observed data, the percentage of current speed less than 10 cm/s was more than 90%, and the current speed can reach 20 cm/s under strong wind conditions.

Abstract:In this study, by selecting the wetland, farmland, grassland, tamarix chinensis, populus euphratica forest and mixed forest ecosystem in the Heihe River Basin as studying objects, several machine learning algorithms were chosen to simulate and interpolate the latent heat flux data, considering several meteorological factors including the net radiation, temperature, soil heat flux, wind speed, relative humidity, and volumetric water content of soil. These methods included multiple linear regression(MLR), decision tree(CART), random forests(RF), support vector regression(SVR), BP artificial neural network(BPANN), and deep learning(DL). The results show the following: (a)RF, SVR, BPANN and DL obtain the best results in different ecosystems with R² = 0. 8 to 0. 93, R_MSE=21. 730 to 41. 731 W/m², and M_AE=12. 153 to 26. 129 W/m², but the results of SVR in tamarix and mixed forest ecosystems are slightly worse than other three methods with R² decreased by 0. 01 to 0. 02. The results of MLR are the worst with R² =0. 6 to 0. 7 and the results of CART are in between with R²=0. 78 to 0. 9. (b)By comparing whether soil moisture participating in the gap filling, it indicates that the participation of soil moisture can improve the gap-filling accuracy of models to some extent with R² increased by 0. 01 to 0. 06. (c)At the same time, the established gap-filling model was used to interpolate the evapotranspiration of other years, and it is found that the accuracy of gap-filling result decreased in varying degrees. With comprehensive consideration of the accuracy and stability of these models, it can be found that RF, BPANN and DL are more suitable for the gap filling of evapotranspiration, and the participation of soil moisture can improve the accuracy of three models.

Abstract:To improve the reliability of parameter identification in the hydrologic modelling, this study combined auto regressive model with Markov chain Monte Carlo method, and proposed an auto regressive(AR)model based modified Markov Chain-Monte Carlo(AR-MCMC). The residual covariance matrix in the traditional MCMC method is modified by using the AR model. Based on a case study of snowmelt runoff model(SRM)in Xinjiang’s Tiznavu watershed, it can be found that the residual sequence of snowmelt runoff simulation has significant autocorrelation. By correcting the residual covariance matrix, the marginal likelihood of AR-MCMC is larger than that of MCMC. Based on the assessments of multiple indexes, AR-MCMC method has a better prediction interval than MCMC. In addition, when comparing the Nash coefficients in calibration and verification periods, they are 0. 86 and 0. 89 respectively for AR-MCMC, while 0. 84 and 0. 87 respectively for MCMC. Therefore, the snowmelt runoff simulation obtained by AR-MCMC method is better than that obtained by MCMC.

Abstract:In order to improve the calculation method of converted permeability coefficient in karst conduit flow, based on the Izbash’s exponential equation, the formula of converted permeability coefficient for the karst conduit was derived under the condition of considering the local and frictional water-head loss. The rationality of this method was validated by establishing a bent karst-conduit model. Based on this model, the sensitivity analyzing method of single factor was used to discuss the response of converted permeability coefficient to the Reynolds coefficient of current, the diameter and bending angle of karst conduit, and the calculated length of karst conduit, under four flow patterns including the laminar flow regime, hydraulic smooth regime, hydraulic second transition regime and hydraulic rough regime. Two results can be obtained: (a)When the karst conduit is short, the sharp changes of large Reynolds coefficient and flow boundary conditions will produce large local-head loss. Under the condition of considering the local-head loss, the derived converted permeability coefficient is more consistent with the actual situation. (b)The influence of the diameter of karst conduit on the converted permeability coefficient is the largest, while the Reynolds coefficient only has a great influence on the laminar flow regime. The influence of the Reynolds coefficient, bending angle and the calculated length of the karst conduit in other three flow regimes is smaller than that of the conduit diameter.

Abstract:Due to the large scale, large flow velocity and complex flow structure, it is very difficult to measure the flow structure of the confluence of Yangtze River and Poyang Lake. In this study, Acoustic Doppler Current Profiler(ADCP)was used to measure the velocity and the water depth through 17 cross-sections. Kinetic energy correction coefficient(α)and momentum correction coefficient(β)were used to characterize the mixing of two flows. In addition, pH, dissolved oxygen, electrical conductivity, and suspended sand concentration were also measured. The results show that the two branches of the Yangtze River around the Guanzhou mixed quickly because of their similar flow velocity and bed discordance, while the Yangtze River and the Poyang Lake completely mix till 2. 6 km downstream where α and β are about 1. 3 and 1. 15, respectively. A 300 m stagnation area and twin surface-convergent helical cells were observed. The circulation strength of secondary flows can reach about 0. 6 and attenuates downstream. Due to decrease of width-depth ratio and effects of local wharfs, only one unidirectional counterclockwise helical cell occurred in the last two sections, and the circulation strength was lower than 0. 1.

Abstract:In order to protect elver resources in China and to solve the obstruction effect of low-head water-power engineering in the back migration of elvers, based on the indoor monitoring data from June to August, 2017, the passing efficiency of fishway, trajectory of behavior and swimming speed were evaluated by statistical analysis for the eel channel with weir surface roughing. This study shows that the passing efficiency was significantly different between the experimental group(with rough on the downstream face)and the control group(without rough on the downstream face), the migration success rates of which were 82. 5% ± 2. 5% and 13% ± 4. 79%, respectively. Compared to the control group, the elvers of the experimental group were more active in the process of back migration and its form was like the snake crawling, which showed S, Z and straight type. Besides, the edge-oriented movement was more obvious, and was a typical kind of behavior of climbing to the top of a weir though a typical burst swimming events, the maximum explosive speed of which reaches up to 0. 66 m/s.

Abstract:This study applied a nonstationary harmonic analysis(NS_TIDE)method to analyze the long-term monitoring data of 6 stations in the Yangtze Estuary, and the spatial and temporal variations of multiple sources of tidal asymmetry were quantified by a skewness metric. The results indicated that the tidal skewness shows an initial increase followed by a slight decrease as it propagates landward. The detailed amplitude variations of tidal asymmetry due to changes in the seasonal discharge were investigated. The sensitivity analysis reveals the response of tidal asymmetry to the varying discharge, which is the tidal asymmetry of upstream decreases with the increase of discharge and the tidal asymmetry of downstream shows a opposite trend. The results spanning the periods before and after the operation of the Three Gorges Dam were compared to investigate the impacts of the Three Gorges Dam. Because of the decrease in river discharge during the flood season, tides became more asymmetric at the upstream region, but a contrary trend appears at the downstream region.

Abstract:In order to understand the wave propagation and evolution mechanism on the slope seabed of good permeability, the wave propagation characteristics on the fine gravel slope seabed were tested in the flume. The pore water pressure responsing characteristics of the seabed soil, the near-bottom horizontal velocity characteristics of wave in the shallow water deformation area of the slope seabed, and the wave propagation and evolution characteristics on the permeable slope seabed were studied. The experimental results show that the excess pore water pressure increases with the increase of wave height and wave period. It’s also found that the near-bottom horizontal velocity increases with the increase of wave shallowing degree. Meanwhile, with the increase of wave Ursell number, the deformation of wave shallowing on slope is more obvious, and the wave-wave interaction between harmonics is more intense. In addition, in the initial stage of wave shallowing, the seabed permeability is greater than the effect of wave shallowing, and in the area of severe wave shallowing, the effect of wave shallowing is greater than the seabed permeability.

Abstract:In order to solve the technical problem of deep-water sheet pile wharf on weak soil foundations, which is treated with different cement mixing ratios and cement mixing piles, and combined with the traditional single anchor sheet pile structure, the influence of combined sheet pile wharf structure is studied. The studying results of the force and deformation indicate that the reinforcement of weak soil with different cement mixing ratios can be used to strengthen the weak soil foundation for increasing the stiffness for resisting vertical and horizontal loads, and to reduce the lateral earth pressure on the front wall. With the increase of the mixing ratio, the overall effect of lateral earth pressure is increased, and the deformation of the front wall is significantly reduced. While the cement mixing pile is used to treat weak soil foundation, the mixed pile and the soil between piles are formed to coordinate the stress conditions of structure and soil. By limiting the displacement of the front wall, the internal force of the anchor rod as well as the internal force of front wall is reduced.

Abstract:In order to study the main driving force of reclamation dynamics and land use change in coastal areas, this study selected the coastal areas of Jiangsu province as the research area. Based on the ENVI 5. 3 and ArcGIS 10. 0 software, as well as the data of Landsat-7 ETM remote sensing image in 2000 and Landsat-8 OLI remote sensing image in 2017, the shoreline was extracted by the visual interpretation and classified by the supervised classification method, to obtain the land use information in 2000 and 2017. The driving forces were obtained by the principal component analysis based on the SPSS 20. 0 software. The results showed that during the period from 2000 to 2017, the coastal areas of Jiangsu province were reclaimed on a large scale. The coastal land with area of 107 420. 0 hm² was reclaimed for different uses, at an annual rate of 6 318. 8 hm² and the intensity of coastal reclamation of 7. 11 hm²/(a·km). In the past 16 years, the coastal area of Lianyungang had the lowest reclamation intensity, and most of the farmland, woodland and water were converted into the urban and rural areas, industrial mining and residential land. Besides, the coastline of Yancheng coastal area was longest and the reclamation area was largest, the whole land utilization pattern moved towards the coast, and the area of farmland and unutilized land reduced. In the coastal area of Nantong, the reclamation intensity was largest, the woodland area was decreased by a large margin, and the urban area was increased. Population growth and social and economic development are the main driving forces of coastal reclamation and land use change in coastal areas of Jiangsu province.

Abstract:In order to investigate the mechanical response and interpret the key collapsing reason of old transmission towers under unfavorable conditions of strong winds, an automatic numerical simulation method has been developed with emphasis on the 110 kV ZS-type of overhead transmission towers. The static bearing capacity of components under different load conditions as well as dynamic characters of the structure were analyzed in this study based on the proposed simulation method and mode superposition theory. The results show that the middle section of the ZS-type transmission tower is the weakest section. Thus, the relatively weak middle section combined with insufficient anti-twist capacity of the tower is the main cause of its structural collapse. On this basis, structural reinforcement and performance improvement can be carried out, which were verified by the numerical model.

Abstract:In order to study the mechanical behavior of tight sandstone under complex stress paths, the multi-function rock triaxial test system was used to carry out three-axis cyclic loading and unloading tests with confining pressures of 5 MPa, 15 MPa and 20 MPa, and then, energy evolution analysis was carried out. According to the results of the tests, the compressive strength of sandstone increases with the increase of confining pressure. The axial deviatoric stresses at the maximum compression point with confining pressures of 5 MPa, 15 MPa, and 20 MPa are 80. 68 MPa, 120. 72 MPa, and 152. 12 MPa, respectively. During the loading and unloading process, some of the damage is converted into the internal energy and other forms of energy, so the unloading curve is lower than the loading curve and hysteresis loops appear. As the load increases, the hysteresis effect is getting gradually obvious. The failure of sandstone is dominated by shear failure and produces axial and lateral sloping cracks. Energy evolution analysis shows that the energy dissipation is the cause of damage to the rock mass. The peak elastic energy before the failure of rock sample increases linearly with the confining pressure, and the effect of confining pressure on peak elastic energy is significant as well.

Abstract:Using the fractal dimension and the gradation width to quantify the gradation, the influence of gradation on the maximum dry density, the oedometric modulus and the particle breakage is investigated through a series of oedometric compression tests. The test results show that the maximum dry density of coarse-grained material increases first and then decreases with the increase of fractal dimension and reaches a maximum value when the fractal dimension is near 2. 2. Meanwhile, the maximum dry density of coarse grain increases with the increase of gradation width. The oedometric modulus under a low-stress level is influenced similarly by the gradation. Denoting the transitional stress in double logarithmic coordinates as the crushing strength, the crushing strength of coarse-grained materials increases with the increase of fractal dimension and gradation width. The greater the crushing strength, the smaller the breaking rate of particle. The final gradation of coarse aggregate with different initial gradations converges towards a unique ultimate fractal distribution.