Abstract:To explore the flood control capacity changes and causes of watersheds, an analysis model of watershed flood control capacity was constructed based on the driving force-state-response (DSR) model. The social and economic development, flood control capacity change and water conservancy construction investment in the Qinhuai River Basin were evaluated and analyzed from the three aspects of driving force, state and response. The results show that the rapid development of urbanization construction in the Qinhuai River Basin was mainly concentrated before 2010, and the development slowed down after 2010. The continuous development of human economic construction caused some damages to the flood control capacity of the basin. However,due to the continuous investment in water conservancy engineering construction, the flood control capacity of the basin was basically improved and guaranteed. The storage capacity of the river network still continues to decline, and the construction and management of small and medium-sized rivers remains to be further reinforced.

Abstract:Combining the advantages of the existing machine learning models, convolutional neural network (CNN) and gated recurrent unit (GRU), a parallel convolutional recurrent neural network (PCNN-GRU) model was constructed and was applied to the prediction of daily water level changes at the Waizhou station in the lower reaches of the Ganjiang River. The results show that, compared with long short-term memory (LSTM), GRU and convolutional recurrent neural network (CNN-GRU) models, the root mean square error and absolute average error of the PCNN-GRU model are decreased by 18.39%, 21.11%, 15.48% and 21.31%, 18.64%, 14.28%, respectively, and the Nash-Sutcliffe efficiency coefficient and accuracy rate are increased to 0.999 2 and 88.12%, respectively. This indicates that the PCNN-GRU model has good prediction performance, and can be used for river water level prediction.

Abstract:Based on the measured runoff and tide level data of the long series from 1960 to 2019, Mann-Kendall test and Theil-Sen estimation were used to analyze the runoff variability of the Yangtze River Estuary and the trend of sea level change. In combination with MIKE21 hydrodynamic model and Monte Carlo method, a method for calculating the over standard rate of salinity was proposed, and the risk of saltwater intrusion into the Yangtze River inlet was assessed. The results show that the annual variance of runoff logarithms and the average sea level height show a significant downward and upward trend, respectively. It is estimated that the annual variances of runoff logarithms will decrease by 30% and 60% respectively by 2060 and 2100, and the average sea level height will increase by 0.2 m and 0.4 m respectively. The sea level rise increases the over standard rate of salinity at the Yangtze River Estuary, which is relatively obvious in the middle section of the estuary. With the decrease of runoff rheological anisotropy, the over standard rate of salinity along the Yangtze River Estuary rises and falls alternately. In 2060 and 2100, the over standard rate of the average salinity in the Yangtze River Estuary will increase from 46.9% to 52.2% and 54.9% respectively, in which the influence of sea level change on the saline intrusion in the Yangtze River Estuary is significantly greater than that of runoff variation.

Abstract:Based on the observation data of 127 meteorological stations and historical atmospheric CO2 concentration data in the middle and lower reaches of the Yangtze River from 1981 to 2013, the water demand of rice was simulated with the change of atmospheric CO2 concentration considered or not. The influence of atmospheric CO2 concentration rise on the water demand of rice in the middle and lower reaches of the Yangtze River was analyzed. The results show that, without considering the atmospheric CO2 concentration, the annual average water demand of rice in the middle and lower reaches of the Yangtze River was 400.16 mm, and the spatial distribution was obviously different. The water demand of rice considering atmospheric CO2 concentration decreased by about 1.6% on average compared with that without considering CO2 concentration. For every 1 μmol/mol increase in CO2 concentration, the average water demand of rice in the study area decreased by 0.071 mm. The water demand for irrigation in each sub-basin varies due to different effective rainfall. Considering the change of atmospheric CO2 concentration, the total irrigation water demand for rice in the middle and lower reaches of the Yangtze River decreased by 4.24 km³.

Abstract:In order to deeply understand the internal unsteady flows in vortex pumps, based on the RNG k-ε turbulence model, numerical simulation of unsteady flows was carried out to analyze the vortex cores, turbulent kinetic energy distribution and internal pressure pulsation in different fluid domains of vortex pumps under three flow rates by CFX. The results show that the vortex cores of the inlet pipeline gradually decrease with increasing flow rates. The diameter and flow velocity of the circular vortex band connected end to end in the inner ring increases within the volute, and the vortex cores in the outer ring gradually disperse within the volute. The size of the vortex cores in the transition region of the diffuser tube and at the volute tongue increases significantly. Under low flow and rated flow conditions, the high-brightness turbulent kinetic energy is concentrated in the inner ring of the volute, and the main frequency of the internal pressure pulsation is the rotational frequency of the blade. Under large flow conditions, the high-brightness turbulent kinetic energy is concentrated in the transition area from the volute to the diffuser, and the main frequency is the rotational frequency of the axis. The non-vortex core area in the impeller is mostly concentrated in the upstream surface of the blade. With the increase of the flow rate, the vortex core distribution gradually disperses, and the non-core area increases. The high-brightness turbulent kinetic energy is distributed at the blade inlet under low flow, in the middle of flow channel under rated flow, and at the blade outlet under large flow. The main frequency of the pressure pulsation in the blade flow channel is always the rotational frequency of the axis.

Abstract:To investigate the dynamic process of tailings pond overtopping failure and the mechanism of breach development, three sets of comparable model tests were conducted to systematically analyze the process of breach spreading and the evolution of the breach. A power function formula of the breach spreading rate under overtopping failure mode was proposed. The process of infiltration line change during the reservoir water level rise stage and the change of flow velocity, flow rate, and breach width under different infiltration line depth conditions during the breaching stage was discussed. The results show that the breaching process of tailings dams can be subdivided into three stages, which are diffuse flow and gully formation, dam collapse and rapid expansion of the breach, and stable flow release. The depth of the infiltration line has a major impact on the flow rate, flow velocity, and the final width of the breach. The peak flow rate and the final width of the breach when the seepage fails are 1.5 times those of the normal discharge, and the peak flow velocity can be 1.2 to 1.3 times that of the normal discharge. Reducing the height of the infiltration line can delay the time for the debris flow reaching the downstream of the breached dam, which can extend the emergency evacuation time by about 3 min. The calculated values of the power function formula match the measured values well.

Abstract:Aiming at the problems that the random forest (RF) used in predicting compaction quality of core gravel soil, such as decision tree number selection and ignoring the influence of P0.075 mass fraction on compaction quality, a random forest (FOA-RF) algorithm based on the fruit fly optimization algorithm (FOA)is proposed, and a core wall gravel soil compaction quality prediction model based on the FOA-RF algorithm considering the content of P0.075 is constructed.On one hand, this model can analyze the correlation between material source parameters and dry density, and P0.075 content can be added as the input parameter.On the other hand, the FOA algorithm is used to optimize the random forest, which solves the problem that the RF algorithm is difficult to obtain the optimal solution of decision tree number and does not consider the influence of decision tree number and random feature number at the same time. Finally, taking a gravel-core wall rockfill dam project in construction in Southwest China as an example, the prediction model based on the traditional RF algorithm, BP neural network, multiple linear regression and the FOA-RF model was used to predict the compaction quality respectively. The result shows that the FOA-RF algorithm has superiority in prediction accuracy. Based on this model, a compaction quality prediction module can be developed and embedded in a real-time monitoring system for rolling quality, which can realize real-time prediction of compaction quality.

Abstract:Based on field sampling surveys of aquatic plant species, population status and spatial distribution, the minimum ecological water level of Xuanwu Lake was determined using the lake morphology analysis method and the biological lowest space demand method. The water level regulation scheme of aquatic plants at different growth stages was formulated considering the water level demand of aquatic plants. The results show that the species of aquatic plants in Xuanwu Lake are rich, but the coverage is not high, which is 13.2%. The coverage of submerged plants is very low with a value of 2.1%. The minimum ecological water level of Xuanwu Lake is 9.6 m.The recommended water level during the germination stage is 9.9 m, which can reach the goal of 30% coverage of aquatic vegetation and is beneficial to the germination of aquatic plants, especially submerged plants. The recommended water level in summer is 9.8 m, which can guarantee flood control security, control overgrown emergent plants such as lotus flowers, and promote the growth and recovery of the overall aquatic plants in the lake.

Abstract:To ensure the ecological service function of the rivers in the main urban area of Taizhou City, this study constructed an ecological water demand calculation method suitable for this area based on the analysis of the characteristics of the rivers in this area. This method comprehensively considers the requirements of flow velocity, water level and water quality, and uses MIKE11 hydrodynamic water quality model to quantitatively determine a river water allocation method which can achieve ecological flow velocity, ecological water level and water quality goals. The calculation results have shown that the ecological flow velocity of the main urban river network is 0.1 m/s, and the ecological water level threshold range is 1.8~2.24 m. By fully utilizing reclaimed water as a clean water source supplemented by river replenishment, Taizhou’s main urban river network is meeting the target requirements of water level, flow velocity and water quality in wet years, normal years and dry years. This study provides a decision basis for rationally allocating water resources to maintain ecological health of rivers and lakes in urban river network areas.

Abstract:To investigate the impact of adding parapet walls at the top of the weir and the height of the parapet walls on the discharge capacity of the piano key weir, physical model tests were conducted to compare and analyze the discharge capacity of the piano key weirs with 8 different heights of parapet walls and numerical simulations were conducted to analyze the discharge of each overflow crest, flow pattern and flow velocity of the piano key weirs with 5 different heights of parapet walls. The results show that, compared with the foundation shape, the addition of parapet walls can improve the discharge efficiency and discharge ratio of the inlet and outlet, increase the discharge capacity of the side weir, reduce the overflow collision of the side weir, increase the discharge flow velocity, and as a result, improve the discharge capacity of the piano key weir. When the height of parapet wall is 13% of the weir height, the discharge capacity increases most. When the relative hydraulic head H/P <0.2, the discharge capacity can increase by 8% to 15%. When 0.2< H/P <0.4, the discharge capacity can increase by 10% to 12%.

Abstract:To have a deep insight into the turbulence characteristics of water flow around a perforated siltation-promoting plate, the change law of the turbulence characteristics before and after the plate was analyzed through an indoor generalized water tank test. The three-dimensional instantaneous flow velocity on the typical sections before and after the perforated silting-promoting plate was measured by acoustic Doppler velocimetry (ADV), and the distribution law of time-averaged flow velocity, turbulence intensity, Reynolds shear stress and turbulent kinetic energy at typical sections were also analyzed. The test results show that there is a recirculation zone in the area near the plate back, and the recirculation zone corresponds to the position of the grille of the perforated siltation-promoting plate. The relative turbulent intensity, Reynolds shear stress and relative turbulent kinetic energy behind the plate are significantly larger than those in front of the plate. The plate has a great influence on the flow in the area near the plate back. With the increase of the distance from the perforated siltation-promoting plate, the recirculation phenomenon disappears. The change of the flow velocity tends to be steady, the relative turbulent intensity decreases and finally tends to be stable, and the relative turbulent kinetic energy decreases with a decreased reduction rate. The Reynolds shear stress at the xOy plane close to the near-plate area is greater than that at the yOz plane, and the Reynolds shear stress at the xOy plane adjacent to downstream is close to that at the yOz plane.

Abstract:To effectively suppress the geyser in the storage tunnel system, the suppression effects of two different shaft forms on the geyser are investigated based on the 3-D numerical simulation. The results show that the protruding shaft can induce the separation of the gas-column head, and decrease the local pressure and the kinetic energy of the upper water, resulting in the suppression on the geyser. The shunt shaft can make one bin to undertake the other bin of the upward water, prevent most of the water moving up, and increase the leaky velocity of the upper water, resulting in the suppression on the geyser. The protruding shaft has better suppression effect on the geyser, and the geyser intensity can be reduced by 60%.

Abstract:The research achievements and development trend of hazard chain of landslide surge for high dams and large reservoirs are reviewed. The typical examples of landslide surge disasters in reservoir areas in China are summarized. The research status is reviewed from the aspects of landslide classification, triggering factors, strength parameters of sliding zone, sliding velocity and movement evolution law, landslide surge generation and propagation simulation technology, interaction between landslide surge and hydraulic structures, etc. The applicability and limitation of existing research methods are remarked and the research difficulties, key technologies and problems to be solved are emphatically put forward.

Abstract:On the basis of summarizing the mechanism of water resistance destruction of magnesium phosphate cement (MPC) and its repair mortar, the proportion of raw materials, mineral admixtures, additives and curing conditions, such as the effects of water-cement ratio, mass ratio of dead-burned magnesium oxide and phosphate(M/P), particle gradation of raw materials, type and amount of mineral admixture, type of admixture and maintenance temperature and humidity conditions on the water resistance mechanism were reviewed. The urgent problems in the research and application field of MPC water resistance and its repair mortar were analyzed. The technical ways to improve the water resistance and cost of MPC and its repair mortar were proposed, including incorporating mineral dopants, nanoparticle modification, and preferring and upgrading the quality of fine aggregates.

Abstract:Based on the geometric characteristics of the velocity profile, a new dimensionless method was proposed and combined with the regression analysis of the flume experimental data, the vertical velocity distribution law and turbulent flow sub-division in vegetated open channel were presented. According to the characteristics of variation rate of velocity gradient, two characteristic heights are determined. New dimensionless velocity and height are defined by the characteristic heights and corresponding velocities, water depth and maximum velocity, and the velocity distribution law is further obtained by the dimensionless experimental velocity data. The results show that the proposed dimensionless velocity is logarithmically distributed near the free water surface, and in the region between the logarithmic law zone and bed, it can be represented by a four-piecewise function.According to the applicable region of each distribution function, the flow sub-division is determined. It is found that the boundary heights do not coincide with the characteristic heights, but are approximately equal to the upper and lower boundaries of the mixing layer.The comparison with other studies illustrates that the proposed dimensionless method, the piecewise functions and the flow sub-division are effective for describing the velocity with good applicability.

Abstract:Aquatic plants are an indispensable part of the environment of rivers, lakes and coastal wetlands. The existence of plants changes the hydrodynamic conditions, thus affecting the suspension of sediment and the transport of pollutants. Starting from two hydrodynamic conditions of steady flow and wave, aiming at the flow resistance, flow structure, turbulent characteristics, characteristic velocity, wave attenuation coefficient, sediment movement and pollutant transport under the influence of flexible plants, the main domestic and foreign literatures are reviewed. The interaction mechanisms of vegetation-flow-sediment-pollutant under complex hydrodynamic conditions are proposed as the research focus and difficulty in the future.