Abstract:The nature of watershed hydrological model is discussed. Models are always approximations for prototypes and a model cannot reflect all the characteristics of a prototype, especially for the complicated phenomena such as the formation of rainfall-runoff of a watershed. The role of scientific thinking for decomposition and assembly in the establishment of watershed hydrological models is explained. Substantial progress of watershed hydrological models can be made only if the breakthrough of both the theories for runoff yield and concentration and the assembly methods from basic hydrological phenomenon to watershed hydrological models are realized. The reasons of ill-posed problems in the inverse problems of watershed hydrological models are analyzed. Some shortcomings of the solution for inverse problems of watershed hydrological models by means of direct optimization methods are pointed out. Preliminary ideas on the solution for the inverse problems of watershed hydrological models through big data are proposed. With more accurate and refined hydrological observation, big data method has bright prospects in the solution for both direct and inverse problems of watershed hydrological models.

Abstract:A hillslope infiltration-runoff model in earth-rock mountain regions was established, including vegetation interception, depression storage, infiltration, subsurface flow, and concave and fissures storage of the bed rock. Based on the analysis of the underlying surface characteristics in earth-rock mountain regions, the volume fraction of rock fragments in soils was introduced to qualify their impacts on infiltration. The concave and fissures storage of the bed rock was also considered in the present model. Field experiments on runoff yield and confluence of natural precipitation were carried out for model verification, and the simulation results of the present model were compared and analyzed with that of existing hillslope infiltration-runoff models. The results show that compared with existing models, the model proposed in this paper can well simulate the runoff and infiltration rate, and the measured values are in good agreement with the simulated ones. However, during storm periods, the simulated infiltration rates are far less than the measured ones. A possible reason is that rock fragments in soils may cause the formation of fast flow paths in the earth-rock interface, which is neglected in the present model. This model needs to be further refined and improved to consider the priority flow paths inside the soil layers and bedrock layers in earth-rock mountain regions.

Abstract:To improve the risk management of regional drought disaster, evaluation of agricultural drought vulnerability in Henan and Shandong was conducted. Combined with relevant literature and regional reality, 12 indicators in two perspectives of sensibility and resilience were selected to establish an evaluation index system. The indexes of agricultural drought vulnerability for cities in the study area were calculated by a vulnerability model based on entropy value method and comprehensive index method. Key influencing factors were identified by a factor contribution model. The results show that, relative significant disparity with different vulnerability levels exists among cities in the study area and the overall vulnerability level is moderate. The spatial difference of agricultural drought vulnerability is obvious and the vulnerability in Henan is higher than that in Shandong. The main influencing factors of agricultural drought vulnerability in Henan are the proportion of agriculture population, multiple-crop index and the income of rural residents per capita. The main influencing factors in Shandong are the proportion of effective irrigation area, agricultural water consumption per unit area and the average financial income.

Abstract:Further understanding of the soil water movement in moistube-irrigation can be guidance for engineering design. A mathematical model of soil water movement in vertical moistube-irrigation was established based on the unsaturated soil water movement theory. The model was then solved by the SWMS-2D software. The simulated indexes, including the infiltration capacity per unit length, movement of the soil wetting front and moisture content in the soil profiles were verified by indoor moistube-irrigation experiments. It shows that the simulated results agreed well with measured values, indicating that the model can truly reflect soil water movement during moistube-irrigation. It is feasible to simulate soil water movement for the vertical moistube-irrigation is proved by SWMS-2D.

Abstract:A physical model test for the diversion project of the Fu River into Qinglan Lake was conducted to investigate the siltation and adjustment law of a channel connected to a lake with a gradually widening boundary. The results show that there exists a spatial variation for deposition styles and cross-section adjustment along the channel in the initial siltation state. A stable single channel develops with natural levees in the upper reach. A relatively stable braided channel develops with transverse bars, point bars and longitudinal bars in the middle reach. In the lower reach, siltation bulks of different scales and siltation location adjustment appears accompanying with the phenomena of cut-bank and channel diversion. The reason for such spatial variation has been discussed in the perspective of hydrodynamic and sediment dynamics. The relationship between the mainstream flow velocity and the incipient velocity of median size sediment is an important indicator to determine the adjustment of river bed erosion and deposition, which could possibly be a key reason for the variation of initial siltation along a widening river channel.

Abstract:To ensure the safety of the protective structures of a stilling basin under high speed flow, stilling basin with a steel membrane is proposed as a new type of protective structure in which is a layer of thin homogeneous perforated steel plate is laid on the stilling basin slab. Based on hydraulic model test, the effect of the uniform perforated steel membrane on the distribution of the fluctuating pressure acting on the upper surface of the slab was studied. The results show that, when the uniform perforated steel membrane is laid, the fluctuating pressure intensity coefficient of the upper surface is reduced and the probability density function basically follows the normal distribution with more concentrated range of fluctuating pressure amplitude in the water rolling zone at the front of the stilling basin. The correlation and the spatial integral scale of the longitudinal points decrease, indicating that the vortex retention is reduced. The dominant frequency of the fluctuating pressure is basically the same, but the pressure fluctuation energy has a narrower band. Compared with the pervious slab, the protective structure of steel membrane can effectively reduce the fluctuating load acting on the upper surface of the slab in the front of the stilling basin, indicating that this new type of protective structure shows certain feasibility.

Abstract:Taking the seawalls of power facilities in the high shoal and steep slope topography of an island in Zhoushan, Zhejiang as an example, 3 factors that influence the seawall overtopping rate, including the berm width, the berm superelevation and the height of the parapet wall were studied respectively by physical model experiment and sensitivity analysis was carried out by the method of variance analysis. The results show that the most significant influencing factor of the wave overtopping is the berm superelevation, then the height of the parapet wall and the berm width is the least. The dimensionless wave overtopping rate exhibits obvious exponential relationship of decrease with an increase for the top of the parapet wall superelevation. A reasonable layout method of the seawall structures for power facilities is proposed based on the above analysis.

Abstract:Focusing on the problem that the spawning time of the Chinese sturgeon has been delayed to November due to the impoundment of the Three Gorges Reservoir(TGR), this paper studied one of the key factors, water temperature, that influences the reproduction process. Based on the measured water temperature and meteorological data at typical cross-sections upstream and downstream of the Three Gorges Dam and the Gezhou Dam, water temperature variation during the first decade after the impoundment of TGR(2003-2012)and its effects on water temperature characteristics in the Chinese sturgeon spawning reach located in the downstream of Gezhou Dam were analyzed. The result shows that after the impoundment of TGR, water temperature in the reservoir is higher than before, having substantial effects on the downstream reaches. Local air temperature variation is closely related with the water temperature variation and it can be a fundamental reason for water temperature rise in the spawning reach, accounting for a contributing degree of about 61%.

Abstract:Water intrusion from the mainstream into tributaries frequently occurs since the Three Gorge Reservoir(TGR)impounded. To explore the hydrodynamic characteristics of the mainstream-tributary water exchange process, field observation was carried out to obtain the monthly data(from September 2012 to July 2013), including the hydrodynamic parameters, temperature and turbidity of the Caotang River, a typical tributary in the central area of TGR. Water exchange in different impoundment periods and its influences on water environment of the reservoir were analyzed. The results show that there is a clear bi-directional flow structure in the estuary of the Caotang River and the distribution patterns of the inward and outward flow varies in different periods at the mainstream-tributary interface. The effective flow exchange in most months of a year at the estuary of the Caotang River is higher than that in other tributaries due to the unique river orientation. The water in the mainstream can intrude into the end of Caotang Bay all year round. During the high water level operating periods, inflow and outflow in the estuary shows vertical stratification and good continuity while during the low water level operating periods, horizontal circulation occurs with poor continuity.

Abstract:To study the role of riparian vegetation in the lateral migration of a riverbank and the effect of migration on the distribution of vegetation community, in-situ investigation and analysis of vegetation biomass in the slump blooks and vegetation diversity of the convex bank were carried out along the meanders of the Lanmucuo River in the source region of the Yellow River. A method for estimation of the migration rate of the riverbank was proposed. The results indicate that the migration rate is exponentially correlated with the vegetation biomass. Siltation of the convex bank under different recurrence floods formed five different vegetation bands corresponding to five typical vegetation communities. The lateral migration of the river has a moderating effect on the riparian vegetation ecosystem. A pasture regeneration mechanism was formed with a characteristic that the amount of pasture increased first and then decreased. The continuous primary vegetation succession played an important role in maintaining the long-term sustainable grazing function.

Abstract:Based on the data source of the remote-sensing images of Landsat TM in 1990-2011, object-oriented ENVI method and Google Earth were used to analyze the land cover as well as spatial distribution patterns of natural river networks and artificial ditches. Combined with the annual precipitation and temperature data in 1967-2012, the impact of climatic change on land cover was analyzed. The results show that the area of construction land and desert in 2011 is 5.84 and 1.35 times of that in 1990, respectively. Forestland area decreased with a rate of 0.66 km²/a under the influence of population increase and human activities. Water surface area was in a fluctuating variation due to the influence of both hydrological cycle and precipitation. Grassland area always increased, in which the vegetation coverage decreased first and then increased. The peatland swamps rapidly shrank at a rate of 78.62 km²/a due to the combined effects of climatic warming, artificial ditches and headward erosion of natural river networks. There are two primary dewatering patterns of peatland swamps in Zoige Plateau, dewatering by artificial ditches and joint dewatering by both natural river networks and artificial ditches. Persistent dewatering by artificial ditches significantly influences the water storage capacity, restricts the maintenance of peatland swamps and accelerates their shrinkage.

Abstract:For the problem that the seepage force should be considered in the static and dynamic calculation of the concrete connecting section and the homogeneous loam section of a reservoir dam, a method for calculating the seepage force is proposed. A new Fortran subroutine was developed in this study to be implemented into the commercial finite element software MSC. Marc, and the whole seismic response process of the dam was simulated and analyzed. The calculation results show that, under the design earthquake with a 10% exceeding probability in 50 years, the absolute horizontal acceleration response extremum of the dam body is 5.0 m/s²and the maximum amplification factor is 7.70. The maximum permanent deformation under vertical earthquake is mainly concentrated at the maximum cross section near the top of the dam and the earthquake subsidence is about 0.06% of the dam height. The maximum ground motion acceleration and the dynamic displacement response is located at the local of the dam crest. It can be concluded that there is an obvious “whiplash effect” on the dam crest where seismic strengthening should be carried out. The design and filling standard of each district is reasonable as well as the dam filling scheme, and the seismic safety of the dam is good.

Abstract:Due to the land limitation, layout of an urban water pumping station is generally cramped and reflux, whirlpool and other undesirable flow patterns can easily be produced in the forebay of a pumping station. In order to improve flow patterns, an urban water pumping station that inlets water at the bottom of a water culvert was taken as an example. Numerical simulation of the flow patterns based on RNG k-ε turbulence model in the forebay of the pumping station was carried out and rectification measures for urban water pumping stations of the same type were proposed. It is found that large scale circumfluence exists on both sides of the forebay of the pumping station and the flow distribution of the suction sump is unbalanced, which can cause a bad inlet condition for the pumps. Rectification measures that combined with splay shaped diversion piers and sills can effectively disperse the dense central mainstream, eliminate the large scale wall shedding on both sides of the forebay and homogenize the inflow of the suction sump. These measures can help to improve the inlet conditions for the pumps and to increase the reliability of the pump station operation.

Abstract:A combined method of field data analysis and shaft system simulation is utilized in this paper to investigate the vibration characteristics of a Kaplan type hydro-turbine and a semi-umbrella type generator unit with two guide bearings under electromagnetic forces. Vibration data of variable excitation test was analyzed to summarize the vibration characteristics due to electromagnetic forces in the field test. A computational model combined with finite element method(FEM)model for the shaft system and a simplified analytical method for the unbalanced magnetic pull was then established to simulate and validate the dynamic response of the shaft system under the effect of electromagnetic forces. The results show that, for generator units of such type, a significant shift on the axis center can happen after excitation. Meanwhile, the vibration amplitude is increased significantly at the upper guide bearing but slightly reduced at the turbine guide bearing. The simulated results agree well with the field test results, indicating that the simulation analysis is reasonable and the reason of the vibration phenomenon can be well revealed.

Abstract:Relationship between the autoclave-treated expansibility of cement mortar, one-graded concrete and the autogenous volume deformation of three-graded MgO-mixed concrete at six-year age for the three-graded fly ash concrete commonly used in water retaining dams of water conservancy and hydropower engineering were studied based on the methods such as autoclave-treated test, autogenous volume deformation observation, mercury intrusion porosimetry, scanning electron microscopy, energy-dispersive X-ray spectroscopy and so on. The results indicate that there is no relevance between the autoclave-treated expansibility and the autogenous volume deformation. The current standard to determine the limit MgO content in dam concrete is based on the inflection point of the autoclave-treated expansibility curve or the autoclave-treated expansion ratio at 0.5% of cement mortar and one-grade concrete samples. This standard can ensure the safety operation of a concrete dam but the actual expansive deformation of MgO-mixed concrete cannot be reflected.