Abstract: A comprehensive understanding of the spatial and temporal distribution of precipitation in mountain areas is of great significance for improving the simulation accuracy of regional water cycle processes,as well as the level of water management. In view of the fact that there is a severe lack of ground monitoring in high altitude areas,as well as the disadvantage of downscaling of satellite precipitation products by a single method,this study selects the Taihang Mountain as the research region and establishes a downscaling correction model. The model consists of the validation module and the downscaling module,which includes the multiple linear regression,the partial least squares regression,and the geographically weighted regression. Using the model,the original TRMM data is scaled from 0.25° to 0.05°. The distribution of the wet and dry seasons and the vertical distribution of the annual and monthly precipitation of the "pixel-catchment-region" are analyzed on the basis of the evaluation and optimization of the downscaling results. The research results are as follows: ① The geographically weighted regression is the most effective,reducing the root mean square error and average relative deviation of the corrected and gauged precipitation series,as well as improving the coefficient of determination. The partial least squares regression can reduce the two errors,but it cannot improve the determination coefficient. The multiple linear regression cannot improve any of the three indicators. ② The precipitation on the east and south slopes on the windward side of the summer monsoon is generally higher than 500 mm,while that on the west and north slopes on the leeward side is lower. The zones of the maximum annual precipitation are located in the southeast slope at an altitude of 1 300—1 500 m. ③ The precipitation from July to September accounts for 58.7% of the entire year;the ratio of precipitation in the dry and wet season is 1∶18;and the ratio in each catchment ranges from 1∶13 to 1∶25. ④ The variations of wind direction of the monsoon affect the moving track of the precipitation center,and the vertical zonality is more complicated in the windward than in the leeward.
Abstract: The spatial-temporal characteristics of precipitable water vapor and water-vapor flux as well as precipitation conversion efficiency in the Three River Headwaters Region were discussed through correlation analysis,trend analysis,accumulative anomaly and inverse distance weight based on relevant ERA-Interim reanalysis data from 1979—2016. Some conclusions could be drawn: ① The annual average water-vapor fluxes along the longitudinal and altitude directions in the past 38 years were 2.0 kg/(m·s) and 10.3 kg/(m·s),respectively. The altitude growth rate of water-vapor flux was higher than that of the longitudinal one. The altitude change of water vapor was mainly input,whereas the longitudinal change was mainly output. ② The precipitable water vapor increased slightly. The annual and seasonal means were 1 791.6—2 278.9 mm and 122.2—1 134.2 mm,respectively. The spatial difference in different seasons was significantly large. ③ The annual average precipitation conversion efficiency in the study area was 24.6% and it reached the peak (32.8%) in 1989. Constant spatial distribution was observed to seasonal and annual average precipitation conversion efficiencies. Both seasonal and annual average precipitation conversion efficiencies decreased gradually from southeast to northwest. Moreover,a great seasonal difference of precipitation conversion efficiency was recognized. ④ Although there were abundant atmospheric water resources in the study area,the natural precipitation conversion efficiency was low,which indicated the promising potentials for development.
Abstract: Groundwater in a many regions is an important support or supplement for ecological stability,the critical depth of recharge of surface vegetation by groundwater is critical to groundwater management and ecological security. Taking the West Liaohe Plain as an example,five results were concluded as follows:① The moisture movement structure in vadose zone was innovatively demarcated based on recharge of the vegetation by groundwater,and the mechanism and physical process of recharge of the vegetation by groundwater were described,and the critical depth of recharge of the vegetation by groundwater and related physical concepts were defined. ② According to the physical mechanism of absorbing the phreatic evaporation by the root system of the vegetation,the phreatic water affected layer which is formed by the rise of the capillary water is the key to critical depth. ③ The rational formula of the soil effective pore size was deduced,and the porosity parameter was calculated based on crystal structure model of soil particles,which dissolved the precise calculation of the maximum height of capillary water. ④ The calculation model for critical depth of recharge of the vegetation by groundwater was built by thickness of the root system. ⑤ The results were confirmed by massive field surveys. The results of the study were timely applied in the Horqin Grassland.
Abstract: The design of the rain gauge network affects the accuracy of model simulation. Therefore,studying the effect of rain gauge density and its distribution on improving runoff simulation accuracy and reducing the modeling uncertainty is of vital importance. In this paper,the Xin'anjiang model and the HBV model were applied to simulate the runoff of the Xiangjiang River basin,and the Bayesian method was used to analyze the runoff simulation uncertainty resulted from resampling of rain gauge networks with different gauge densities and spatial distributions. The results reveal that increasing the rain gauge density can reduce the estimation error of areal rainfall,which in turn,improves model simulation accuracy;optimizing the rain gauge number and location can reduce the uncertainty of areal mean rainfall,thereby improving the runoff simulation accuracy;under the same rainfall input and parameter sampling methods,the simulation uncertainty of the Xin'anjiang model and the HBV model has similar characteristics,but the overall simulation accuracy of the Xin'anjiang model is higher,and the uncertainty of the HBV model is bigger.
Abstract: Low Impact Development (LID) measure is a type of sustainable engineering measure to solve the urban water problems. The runoff-control rate is considerably affected by the initial hydrological conditions. Through using Storm Water Management Model (SWMM) for Tianfuheyuan Residential Community in Xixian New Area,this work simulates the runoff control and flood peak reduction under different initial conditions for LID and traditional-development measures,respectively for a set of storms with different return periods. The results indicate that:① The runoff-control rates of natural,semi-saturated and saturated LID measures are 64.3%—83.2%,56.3%—76.5% and 48.7%—68.1%,respectively. Compared to the natural condition,the runoff-control rates in the semi-saturated and saturated conditions are reduced by 6.7%—9.1% and 15.1%—15.8%,respectively. As the rainfall return period increases,the reduction value of runoff-control rate increases at the beginning but then decreases. ② The runoff peaks are 23.3—189.4 L/s,25.9—198.4 L/s and 28.8—290.7 L/s,respectively for natural,semi-saturated and saturated LID measures. In contrast with natural condition,the runoff peaks of semi-saturated and saturated conditions increase by 4.5%—20.9% and 22.9%—53.4%,respectively,indicating that the runoff-control effect of LID measures in saturated condition is far lower than that of nature condition. ③ Compared to the traditional development,LID has significant improvement for runoff control rate. The natural and semi-saturated LID measures could significantly reduce the peak runoff,but it increases under the saturated condition with the rainfall return period of 20 years,showing that the saturated LID measures may lead to higher discharge in the sewer networks downstream for heavy storms. ④ Under the same initial conditions,LID measures are able to effectively improve runoff-control rate. The research can help investigate the practical effects of LID measures.
Abstract: The response of karst groundwater level to rainfall features spatial and temporal variability. There is no consensus regarding the groundwater dynamic system structure of the Zengpiyan cave site in Guilin,Guangxi,China. Based on high-resolution data on rainfall water level,the study area was divided into different aquifers. The characteristics and cause of spatial and temporal variability of karst groundwater level's response to rainfall were explored using water level dynamics,correlation analysis,and sliding window cross-correlation analysis. The results show that in terms of the response to rainfall,the water level of aquifers with a high degree of karst development and diffusion flow for water diversion rises and falls slowly,featuring a strong autocorrelation in water level;the water level of aquifers developed with karst conduits rises and falls rapidly,with a fast decay rate of water-level autocorrelation coefficient,a short lag time in response to rainfall,and a multimodal cross-correlation function graph. The extreme non-uniformity of karst development is the primary cause of differences in spatial response. The response lag of the groundwater level to rainfall in the rainy season is much smaller than during the dry season. This is because,in the rainy season,there is a large amount of cumulative rainfall,the buried depth of groundwater is shallow,and the aerated zone is constantly in a saturated or near-saturated state,causing the groundwater supply to become saturated by vertical rainfall infiltration relatively quickly. Further,the frequent rainstorms in the rainy season can generate to a large hydraulic gradient in a short period of time,accelerating the runoff replenishment speed of aquifers. Taken together,the groundwater system of the Zengpiyan cave site consists of 3 sub-runoff systems,i.e. the NE karst conduit,the NS conduit-fracture,and the NE strong runoff zones. The research results can provide theoretical basis and technical reference for the cave site to formulate plans of preventing and controlling underground water hazards.
Abstract: A series of dredging,hydrologic and topographic in situ measured data are collected to study interannual variations and associated causes of siltation in the 12.5 m Deepwater Navigation Channel (DNC). The results show that:the annual siltation intensity of DNC is characterized by a steady decrease. The siltation intensity of the South Channel to the Yuanyuansha Channel in the upper reach of DNC obviously decreased. The siltation intensity of the North Passage was fluctuating from 2011 to 2015,but it decreased in 2016—2017. The decline of siltation in the South Channel to the Yuanyuansha Channel is mainly related to the decrease of bed load transported from the upper reach and the reduction of elevation difference between the nearby shoals and troughes. The project of the Sand-retaining Dike and the deline of the impact induced by typhoons are the main cause of the decrease of siltation in the North Passage in 2016 and 2017.The large runoff in 2016 & 2017 led to the turbidity maximum zone and the position of main siltation in the North Passage moves downward. The effect of fluvial sediment decline on the siltation of DNC has been emerged gradually. In future,due to those influences,the siltation of the South Channel to the Yuanyuansha Channel will experience declining furtherly and maintain a lower value,while the siltation in the North Passage also will keep a steady downward trend.
Abstract: Flocculation is the primary cause of fine sediment deposition in the Three Gorges Reservoir (TGR),and the critical conditions of flocculation is of great significance to the law and simulation of the sedimentation in the TGR. Field measurements of sediment flocculation were carried out at the Zhongxian and Fengjie reaches in the TGR during the flood season. Based on the acoustic backscatter intensity from ADV and sediment sampling,the instantaneous flow velocities and sediment concentrations were measured synchronously. The sediment settling velocities and floc sizes were calculated using the sediment diffusion theory. The relationships between flocculation degree and particle size,flow velocity and sediment concentration were obtained,respectively. Results show that the sediment flocs are mostly in the region of middle and light flocculation,but less in the region of heavy flocculation. The critical particle size of the sediment flocs is about 0.018 mm,the critical flow velocity is about 0.7 m/s,and the critical sediment concentration is about 0.8 kg/m3. This research can provide theoretical supports for the basic law of sediment transport and simulation of sedimentation in the TGR.
Abstract: To illustrate the formation mechanism and movement characteristics of the maximum turbidity zone in the strong-tidal estuary,this study systematically investigated the main factors affecting the formation of the maximum turbidity zone and its response relationship with estuarine landforms in the well-mixed estuary by analyzing the measured data.By considering the effects of viscous fine sediment movement characteristics and the influence of salinity,this study developed a mathematical model of the maximum turbidity zone in the strong-tidal estuary,which was used to simulate the migration process of the maximum turbidity zone in the dry season of the Jiao (Ling) River.The results show that:the maximum turbidity zone in the strong-tidal estuary arises from the interactions of complex dynamic factors (e.g.,tidal wave deformation,saltwater-freshwater mixing,sediment flocculation and re-suspension) under certain estuary boundary and sediment conditions. Also,tidal wave deformation and sediment supply are the key factors affecting the formation of the maximum turbidity zone. In addition,this study revealed that simulations of the largest turbidity zone in the strong-tidal estuary should fully consider the all the factors,such as tidal current,saltwater-freshwater mixing,periodic movement of viscous fine sediment,flocculation and sediment compaction. The mathematical model can be used to study maximum turbidity zone in strong-tidal estuary.
Abstract: To examine the effect of a vertical plate positioned in front of a rectangular orifice on the time-averaged flow characteristics of a three-dimensional turbulent wall jet,we measured three important quantities: U velocity profiles,velocity half-width,and maximum velocity decay rate with various Reynolds numbers and submerged depths by using particle image velocimetry (PIV). The jet flow field was found to be divided into three major decay regions in terms of the maximum velocity decay exponents:a natural three-dimensional turbulent wall jet region (region I),a vertical plate affecting region (region II),and a near-wall region (region III). In region II,the focus of the present study,the variations in the three measured quantities with downstream distance were found to be independent of the Reynolds number. Compared with the natural wall jet,the confined jet developed substantially faster,and the spread rates in both the longitudinal and lateral directions were significantly higher,owing to the presence of the vertical plate. The spread rate in the symmetry plane was 0.043 within the range of H—1.75H. The lateral spread rate was slightly sensitive to a water depth interval of 0.5H,and the growth rate correspondingly increased from 0.205 to 0.270. Furthermore,the maximum velocity decayed dramatically in this region,with an exponent value of 1.095,and was independent of water depth. The flow characteristics of region II,compared with the natural case,were similar to those in the radial decay region. Therefore,the flow field in region II appears to have fully developed and entered into the radial decay region in advance.
Abstract: The diversion tunnel of high arch dam located in canyon areasruns through the initial to middlestages of dam construction. Investigating the creation and solution of a diversion risk model of the initial and middle stages of high arch dam construction is therefore important to the design optimization of diversion tunnels. The present work focuses on the engineering design stage and makes use of the dynamic simulation technology of high arch dam construction to collect morphological data covering water retaining and dam protection from the initial to middle stages of construction. We here established a risk model of flow diversion in the initial through middle stages for high arch dam construction considering the factors of hydrology and hydraulic randomness,and a method of solving the risk model using Monte Carlo method,which couples with the water retaining and dam protection morphological data and the major random factors,is proposed in this work. Based on the principle of risk analysis,a risk recognition method for the design of diversion tunnel is proposed,and the mathematical model and detailed steps for the design optimization of diversion tunnel dimensions are given. The results of the case study of a high arch dam in the upper reaches of Jinsha River show that the proposed risk model and the solution method are applicable and effective;the model can be used to determine the risk rate of the initial to middle stages of the entire construction project,and it can objectively reflect the two possible water retaining conditions of the high arch dam during the middle stage of the dam protection period and overcome the limitations of the initial diversion risk model;during the middle stage of construction,the diversion risk rate decreases with the increase in diversion tunnel dimensions;and the feasible scheme set of diversion tunnel dimension designs has a boundary,i. e. the optimal scheme. The outcomes of this study can provide theoretical support for risk decision-making and design optimization for the construction of diversion structures for high arch dams.
Abstract: Upstream areas are the major flood contributing areas in humid regions. Upstream hillslopes,valleys and ephemeral channels provide quick pathways for flows during flood events. These pathways generate flows seasonally and only after a rainfall event,i.e.,the hydrological connectivity is ephemeral. Thus the dynamics of drainage networks such as expansion/contraction,and connection/disconnection,may offer important clues to understanding the patterns and processes of runoff generation. However,the mechanism of what controls the hydrological connectivity and how it connects the hillslope,valley and channels is yet to be understood. Extensive field studies in diverse catchments around the world continue to characterize and catalogue the enormous heterogeneity of hillslope structures and complexity of rainfall runoff processes in multiple watersheds,and at different scales. But,these field findings seem to be meaningless for the modeler,as they usually fail to incorporated the experimentalist's knowledge into their models. There is plenty of knowledge gap in the fundamentals with regard to how catchment are composed,organized and connected through hillslopes,valleys and channels,and how catchment storage affects rainfall-runoff responses. In this study,through comparisons of hillslope experiments,we find that process based connectivity is deeply affected by hillslope soil depth,bedrock terrain and drainage network structures. This review also showed that present research works are focusing on micro-scale mechanism (e.g.,soil pores and flow),and there is a gap between the hydrological connectivity experiments and the modelers. We suggest that experimentalists should find a macroscale pathway hidden in the critical zone that is the pivot of the runoff generation and shapes the flow hydrodynamics in the entire catchment. That is to say hydrological connectivity of hillslopes,valleys and ephemeral channels should focus on the cumulative effects of hillslope processes instead of individual soil pore processes. Finally,there should be a balance between conceptualizing of complex hillslope structures and moderate depiction of runoff generation.
Abstract: Karst critical zone is in the five circles intersection area of rock,water,soil,atmosphere and biology. Correct understanding of the structure,function and hydrological cycle process of the karst critical zone is a key problem in the study of the earth critical zone and karst water sciences. This paper analyzes the hydrological cycle process and evolution law in karst critical zone,the effect of hydrological cycle in karst critical zone,explores the rule and driving mechanism of water cycle evolution in karst critical zone under changing environment,summarizes the shortcomings,problems,and proposes the general trend and direction of future research:Interaction mechanism of formation and evolution of karst critical zone and hydrological cycle process;The process of material transformation and energy migration driven by hydrological cycle in karst critical zone and its coupling;Response of hydrological cycle process to global change and human activities at different spatial and temporal scales;Comprehensive application of multiple observation and simulation methods.
Abstract: Coral reef hydrodynamics is an interdisciplinary subject involving the knowledge of ecology,environment,geology and engineering. This subject not only offers theoretical reference for the ecosystem protection and the coastline evolution around the reef island,but also serves the decision-making process for the reef-coast hazard prevention and the reef-island engineering construction. In this study,based on a comprehensive literature review as well as the author’s previous work,the state-of-the-art research advances on coral reef hydrodynamics are summarized in view of the following four aspects:field observation,theoretical analysis,laboratory experiment,and numerical simulation. The research prospects are subsequently provided as follows:the field observation could focus on those reefs in South China Sea,the theoretical analysis could attempt to use the nonlinear wave theory,the laboratory experiment could reproduce the hydrodynamics at field scale based on the large-scale wave flume as well as the wave basin,and the numerical simulation could turn to the Computational Fluid Dynamics (CFD) to simulate the interaction between wave and reef at finer scale. This study serves to guide the future relevant researches on coral reef hydrodynamics in China.