Abstract:A flood forecasting model for small and medium-sized rivers, based on the short-term nowcasting and fine ensemble gridded precipitation forecasts, is established for increasing the flood foresight period. The model adopts the percentile correction method to develop the mapping relationship between the precipitation forecast field of numerical model and the observed field. Based on the GRAPES-3KM model and the Time-Lag-Ensemble fusion technique, a short-term ensemble precipitation forecasting that is consist of three members(the optimal, maximum(95% quantile)and minimum(5% quantile))is developed with the Bayesian model. Taking the developed ensemble precipitation forecasts as the driving force of GMKHM, the hourly real-time rolling forecasting of flood for small to medium-sized basin is performed. The Tunxi Basin of the Xin’anjiang River is selected as the experimental basin to test the real-time flood forecasting in 2020 flood season. Results show that the developed model performed well, the peak discharge of the Tunxi hydrological station was forecasted with 7 hours in advance, the relative error was 5. 6%, and the peak time difference was -1 hour. Compared with that without considering the precipitation in lead-time period, the flood forecast lead-time can be increased by 4 hours with the optional precipitation forecasts and 13 hours with the maximum and minimum precipitation forecasts. The developed model has certain reference significance for the flood forecast of similar basin. The span between maximum and minimum forecasts presented the trend of decreasing gradually since 9: 00 on July 7th. It is of great significance to improve the flood risk prevention and control ability of small and medium-sized rivers with introducing the ensemble nowcasting and short-term precipitation forecasts.

Abstract:The flood early warning and forecast platform needs to be supported by many hydrological data, and to deal with the absence and anomaly of hydrometeorological data in small and medium-sized rivers, this study proposes the quality control technology and method of multi-source hydrometeorological data. The model encapsulation service technology with state and interaction characteristics is studied and developed in cloud environment to provide multi-level on-demand services of data, algorithms, and models. The vertical channel inundation algorithm of small and medium-sized rivers is proposed, and the visualization of flood inundation based on UE4 virtual engine is realized. Based on above key technologies, an intelligent flood forecasting and dispatching platform for small and medium-sized rivers is developed. At present, the platform has been applied in the Tunxi demonstration basin in Anhui Province, and extended to the Qinhuai River in Nanjing and Zhangzhou of Fujian Province, providing important support for the flood prediction and early warning of small and medium-sized rivers.

Abstract:Based on the distributed Xin’anjiang model, the model concentration structure was modified by aggregating the small reservoirs within the sub-basin into a virtual reservoir, aiming to study the storage and discharge effect of small reservoirs on the flood process. Taking Dongfanghong Reservoir, a key medium-sized reservoir in Anhui Province, as an example, 14 floods occurred at the beginning, middle and end of flood season during 2014-2017 were simulated by the distributed Xin’anjiang model, which neglected the influence of small reservoirs. It is shown that the model can well simulate relatively large floods in the middle flood season, but not so well for floods in the end of flood season. Taking two flood events occurred in the end of flood season, No. 2015090420 and No. 2017070101, as examples, the distributed Xin’anjiang model considering the influence of small reservoirs was employed to simulate the storage and discharge effects of upper small reservoirs(Wuliyuan and Gaoe reservoirs)on the floods for Dongfanghong Reservoir. According to the comparison, it is found that the results of the Xin’anjiang model with the virtual reservoir in the sub-basin are better than those of the Xin’anjiang model, with the relative error of runoff depth decreased by 23. 2% and 18. 4% respectively, the relative error of flood peak decreased by 52. 2% and 53. 5% respectively, and the Nash efficiency coefficient increased by 0. 92 and 0. 42 respectively.

Abstract:The utilization of tidal stream energy has become one of the hot research topics in the field of ocean renewable energy. In this study, the distribution status of tidal stream energy resource and classification of tidal stream energy converter(TSEC)were summarized, and the current main demonstration projects of tidal stream energy at home and abroad were introduced. The key technologies of TSEC including the assessment of tidal energy resources, the safety and stability of TSEC, the utilization efficiency and multi-complementary of ocean renewable energy, the wake effect, and the environmental impacts of TSEC array have been discussed. Although the development of TSEC is feasible and necessary, there are still many challenges and difficulties to be solved.

Abstract:To effectively solve the uncertainty problems in the multi-objective decision-making, a comprehensive weighting method considering the fuzzy interval of subjective and objective factors is proposed in this study. The fuzzy analytic hierarchy process(FAHP)was used to determine the subjective weight reflecting the subjective preference of decision makers, and the concept of distance degree of interval number was introduced to extract objective decision information. Then, with an improved comprehensive weighting method based on the game theory, the comprehensive weighting value is determined, and in accordance with this, the scheduling scheme is optimized. The method is applied to the multi-objective optimal scheduling of cascade reservoirs in the lower reaches of the Jinsha River, and the results show that the comprehensive weighting method is feasible in the multi-objective scheduling scheme optimization. The scheduling scheme selected by the comprehensive weight can simultaneously reflect the preference of decision makers and the objective characteristics of each index and has a balanced performance on all indicators. This method provides a new idea for the multi-objective comprehensive operation decision-making of water resources in the basin.

Abstract:To explore the control effect of geological structure on the karst development, this study chose the Westshan mountains of Heqing county as the study area and adopted a combination method of the geological survey and the drilling data, to comprehensively analyze the lithology, geological structure, surface and underground karst phenomena, and distribution laws. The results show that controlled by some tectonic activities, such as the Indosinian orogeny and the Himalayan orogeny, the study area formed an NNE-NE structural pattern. According to the scale, geological structures of the study area can be divided into four scales, regional fault zone, secondary reverse fault, large structural fracture and joint, which affects the karst development in different degrees and controls the flow and drainage of groundwater. Karst development in the study area has stage characteristics, and two planation surfaces of 3 000 m and 2 500-2 700 m are developed. Four levels of river terraces developed in study area, with elevations of 2 300-2 500 m, 2 260-2 320 m, 2 210-2 240 m and 2 200-2 220 m, corresponding to karst caves. Combined with the drilling data, in Westshan mountains of Heqing county, there are three stages of karsts that developed in Paleogene, Neogene and Quaternary.

Abstract:Based on the water balance relationship and hydrogen and oxygen isotope analysis, combined with the hydrogeology condition and tectonic geological structure condition, it is found that the groundwater in basalts of Arshan is recharged by exogenous water, and the recharge source area may be the Tibetan Plateau. The ⁸⁷Sr/⁸⁶Sr ratio of the river and lake water in the Arshan indicates that the strontium in the groundwater comes from the basalt. It is inferred that the groundwater conduiting channel is a continuous basaltic conduit. The low-viscosity alkaline basaltic lava flows form continuous contraction joints during the cooling process, and finally evolve into a pipeline conduiting channel. The leakage water of the Tibet Plateau is rapidly drained to the eastern region through the lava pipeline and the thickening of the mantle lithosphere in the west may be related to the inter basin recharge of groundwater.

Abstract:To explore a new flood control scheme adapting to the current flood pattern, the flood control scheme for “flood discharge from the nearer route” is proposed based on studying the current flood pattern. The effect of river dredging of nearer route on the flood discharge is quantitatively calculated based on the hydrodynamic model for river network in the Pearl River Delta. The results show that the discharge of Modaomen is the largest and the discharge path of Yamen is the shortest in the west four estuaries. Jiaomen had the largest discharge, and its discharge path is also the shortest in the east four estuaries. After the channel dredging, the discharge of Yamen which is the one of the west four estuaries increased by 2. 805×10⁵ m³, and the distribution ratio increased by 0. 50%. The discharge rate of Jiaomen and Humen in the east four estuaries increased by 1. 11 ×10⁵ m³ and 1. 537×10⁵ m³, with a distribution ratio of 0. 20% and 0. 27%, respectively. The flood control scheme has achieved the expected effect, which can provide technical support for the implementation of the Pearl River Delta flood control program.

Abstract:The contact surface between the coarse-grained soil and the stainless-steel blank was tested by an improved direct shear apparatus. Four relative compactness, which is 40%, 55%, 70% and 85%, were used for the coarse-grained soil. The contact mechanical properties of the interface between coarse-grained soil and steel plate and the influence of relative density of coarse-grained soil are studied. The results show that before the interface between coarse-grained soil and steel plate reaches shear failure, the relationship between shear stress and shear displacement is approximately linear. The shear strength and shear stiffness coefficient of the contact surface increase with the increase of relative density of coarse-grained soil. When the relative density increases from 40% to 85%, the cohesion of the contact surface increases by 41. 8% on average, the internal friction angle increases by 35. 4% on average, and the shear stiffness coefficient k_s increases by 11. 2% on average. The tangential stiffness coefficient k_s increases by 40. 3% on average when the normal stress σ_n of contact surface increases from 100 kPa to 800 kPa. Based on the test results, the relationship between the tangential stiffness coefficient k_s, the normal stress σ_n and the relative density D_r is found, and an empirical formula of k_s-σ_n-D_r is proposed, thus a simple contact-surface constitutive model is established.

Abstract:To reveal the response mechanism of bacterial communities of biofilm to nitrate, this study took the submerged macrophyte Myriophyllum Verticillatum as the research object and explored the variations of bacterial community structure and related denitrification genes on the submerged macrophyte under four kinds of nitrate loading(2 mg/L, 8 mg/L, 20 mg/L and 40 mg/L), with the scanning electron microscope, 16S rRNA high-throughput sequencing and PCR amplification technology. The results showed that nitrate stimulated the growth of biofilm but reduced the bacterial α-diversity. The β_SOR diversity index showed that the bacterial community construction under nitrate loading was dominated by species replacements. Proteobacteria, Planctomycetes, Cyanobacteria and Bacteroidetes were the dominant phyla in biofilm. Compared with the control group, nitrate stimulated the growth of denitrifying bacteria(Rhodobacter, Acinetobacter and Bacillus)and the abundance of denitrifying genes(napG, nirS, cnorB, qnorB and nosZ). Network analysis showed that there were complex interactions among the microbes in biofilm. These results indicate that microbial denitrification plays an important role in the process of nitrate removal in wetland.

Abstract:By establishing the three-dimensional numerical model of tunnel, this study investigated the effect of seepage erosion on ground settlement and structural deformation. Firstly, the strength and stiffness reduction approaches were adopted to qualitatively simulate the erosion process based on the triaxial erosion tests. Then a comparison of ground settlements between the field monitoring and the numerical result was conducted to verify the reliability of the numerical approach. The effects of seepage erosion on ground settlement and structural deformation were investigated in the end. The results indicated that the ground settlement induced by the progressive erosion process increased exponentially. The linings were pushed upward due to the erosion-induced unloading as seepage erosion occurred on the tunnel crown, and then resulted in a gradual increase of dislocation of segment joints. The extension of erosion region increased the ground settlement and structural deformation according to the parametric study.

Abstract:Combined with the climate tendency analysis and wavelet coherence analysis, the daily precipitation and temperature data from 1971 to 2017 were used to reveal the spatiotemporal variations of extreme precipitation in the Three River Source Area of the Shaanxi-Gansu-Ningxia Contiguous Region and explore the relationship between extreme precipitation and the El Niñ o-Southern Oscillation(ENSO)activities. The results show that there was a significant increase in extreme precipitation in the Three River Source Area from 1971 to 2017. Precipitation in this region has an apparent spatial pattern with higher values in the south and lower values in the north, showing the apparent impacts of geography and topography. Changes in the extreme precipitation indices in this area are mixed. In most areas, the amount of extreme precipitation, number of heavy precipitation days, and precipitation intensity increase over the study period, while the number of low precipitation days decreases over time, indicating that precipitation in this region tends to become more extreme. There were significant negative correlations between the extreme precipitation indices and the multivariate ENSO index(MEI), and the periods of maximum coherences between extreme precipitation indices and MEI are 3-5 a and 9-12 a.