Deformation and failure mechanism of Yanjiao rock slope influenced by rainfall and water level fluctuation of the Xiluodu hydropower station reservoir

With the construction of the Xiluodu hydropower station on the Jinsha River,the reservoir impoundment began in 2013 and the water level fluctuates annually between 540 m and 600 m above sea level.The Yanjiao rock slope which is located on the left bank of the Jinsha River 75 km upstream of the Xiluodu dam site,began to deform in 2014.The potential failure of the slope not only threatens Yanjiao town but also affects the safe operation of the Xiluodu reservoir.This paper is to find the factors influencing the Yanjiao slope deformation through field investigation,geotechnical reconnaissance,and monitoring.Results show that the Yanjiao slope can be divided into a bank collapse area(BCA)and a strong deformation area(SDA)based on the crack distribution characteristics of the slope.The rear area of the slope has been experiencing persistent deformation with a maximum cumulative displacement(GPS monitoring point G4)of 505 mm and 399 mm in the horizontal and vertical directions,respectively.The potential failure surface of the slope is formed 36 m below the surface based on the borehole inclinometer.The bank collapses of the Yanjiao slope are directly caused by the reservoir impoundment while the deformation area of the slope is affected by the combination of the rainfall and reservoir water level fluctuation.Based on mechanism of the Yanjiao slope,prestressed anchor combined with the surface drainage and slope unloading are recommended to prevent potential deformation.

Influencing mechanism and hydrogeological implications of water level fluctuation of lakes in the northern Qaidam Basin,Qinghai-Tibet Plateau

The Qaidam Basin(QB)is a concentrated distribution area and chemical industrial bases of salt lakes in China.Lakes in the QB have been expanding during the past 20 years.Rapid lake expansion resulted in some considerable scientific issues on the protection of salt lake resources and infrastructure,and monitoring of hydrological processes at the lake-basin scale.Although the spatial-temporal trends of lake changes on the Qinghai-Tibet Plateau(QTP)have been well documented,the underlying influencing mechanism and hydrogeological implications of rapid lake changes in the QB are not well understood.Three lakes in the northern QB were selected to investigate lake water level fluctuations on different time scales based on extensive in-situ monitoring and satellite observations.The influencing mechanism and hydrogeological implications of rapid changes of terminal lakes were discussed in combination with the reported increasing precipitation rate and mass balance of glaciers in the northern QTP.Results reveal the following:(1)the fluctuation pattern of Sugan Lake was asynchronous and out of phase with that of Xiao Qaidam and Toson lakes during the monitoring period;(2)Sugan Lake water rose gradually,and the rise interval was from late April to early July.In contrast,Xiao Qaidam and Toson lakes took on a rapid and steep rise,and the rise intervalwas from late July to September;(3)the influencing mechanisms for rapid lake fluctuations are controlled by different factors:glacier and snow melting with increasing temperature for Sugan Lake and increasing precipitation for Xiao Qaidam and Toson lakes;(4)in accordance with different intervals and influencing mechanisms of rapid lake expansions in the QB,hydrological risk precaution of lakes and corresponding river catchments was conducted in different parts of the basin.This study provided an important scientific basis for assessing the hydrological process and hydrological risk precaution,and protection of salt lake resources along with rapid lake expansions in the arid area.

Effect of Water Level Fluctuations on Wintering Goose Abundance in Poyang Lake Wetlands of China

The Poyang Lake is a Ramsar site and is the important over-wintering site for migratory waterbirds along the East Asian-Australasian Fly way. Examining the effects of water level fluctuations on waterbird abundance and analyzing the influencing mechanism is critical to waterbird protection in the context of hydrological alteration. In this study, the effect of water level regime on wintering goose abundance was examined and the influencing mechanism was interpreted. Synchronous waterbirds survey data, hydro- logical data, Moderate Resolution Imaging Spectroradiometer-Normalized Difference Vegetation Index （MODIS-NDVI） data and habi- tat data derived from Landsat TNUETM data and HJ/CCD data were combined. The satellite-derived Green Wave Index （GWI） based on MODIS-NDVI dataset was applied to detect changes in goose food resources. It was found that habitat size and vegetation conditions are key factors determining goose abundance. Geese numbers were positively correlated with habitat area, while intermediate range of vegetation productivity might benefit the goose abundance. Water level affects goose abundance by changing available habitat areas and vegetation conditions. We suggested that matching hydrological regime and exposed meadows time to wintering geese dynamics was crucial in the Poyang Lake wetlands. Our study could provide sound scientific information for hydrological management in the context of waterbird conservation.

Model test of the influence of cyclic water level fluctuations on a landslide

Many landslides in reservoir areas continuously deform under cyclic water level fluctuations due to reservoir operations. In this paper,a landslide model, developed for a typical colluvial landslide in the Three Gorges Reservoir area, is used to study the effect of cyclic water level fluctuations on the landslide. Five cyclic water level fluctuations were implemented in the test, and the fluctuation rate in the last two fluctuations doubled over the first three fluctuations. The pore water pressure and lateral landslide profiles were obtained during the test. A measurement of the landslide soil loss was proposed to quantitatively evaluate the influence of water level fluctuations. The test results show that the first water level rising is most negative to the landslide among the five cycles. The fourth drawdown with a higher drawdown rate caused further large landslide deformation. An increase of the water level drawdown rate is much more unfavorable to the landslide than an increase of the water level rising rate. In addition, the landslide was found to have an adaptive ability to resist subsequent water level fluctuations after undergoing large deformation during a water level fluctuation. The landslide deformation and observations in the field were found to support the test results well.

Soil anti-scourability enhanced by herbaceous species roots in a reservoir water level fluctuation zone

Revegetation is one of the successful approaches to soil consolidation and streambank protection in reservoir water level fluctuation zones(WLFZs).However,little research has been conducted to explore the impact of herbaceous species roots on soil anti-scourability during different growth stages and under different degrees of inundation in this zone.This study sampled two typical grasslands(Hemarthria compressa grassland and Xanthium sibiricum grassland)at two elevations(172 and 165 m a.s.l.)in the water level fluctuation zone(WLFZ)in the Three Gorges Reservoir(TGR)of China to quantify the changes in soil and root properties and their effects on soil anti-scourability.A simulated scouring experiment was conducted to test the soil anti-scourability in April and August of 2018.The results showed that the discrepancy in inundation duration and predominant herbaceous species was associated with a difference in root biomass between the two grasslands.The root weight density(RWD)values in the topsoil(0-10 cm)ranged from 7.31 to 13 mg cm^(-3) for the Hemarthria compressa grassland,while smaller values ranging from 0.48 to 8.61 mg cm^(-3) were observed for the Xanthium sibiricum grassland.In addition,the root biomass of the two herbs was significantly greater at 172 m a.s.l.than that at 165 m a.s.l.in the early recovery growth period(April).Both herbs can effectively improve the soil properties;the organic matter contents of the grasslands were 128.06%to 191.99%higher than that in the bare land(CK),while the increase in the water-stable aggregate ranged from 8.21%to 18.56%.Similarly,the topsoil antiscourability indices in both the herbaceous grasslands were larger than those in the CK.The correlation coefficients between the root length density(RLD),root surface area density(RSAD)and root volume density(RVD)of fine roots and the soil antiscourability index were 0.501,0.776 and 0.936,respectively.Moreover,the change in the soil antiscourability index was more sensitive to alternations in the RLD with diameters less than 0.5 mm.Overall,the present study showed that the perennial herbaceous(H.compressa)has great potential as a countermeasure to reduce or mitigate the impact of erosion in the WLFZ of the Three Gorges Reservoir.

Effects of water level fluctuation on sedimentary characteristics and reservoir architecture of a lake, river dominated delta

The hydrodynamic conditions present in a river delta's formation are a highly important factor in the variation between its sedimentary regulation and characteristics. In the case of the lacustrine basin river-dominated delta, water level fluctuations and fluviation, are both important controlling factors of the sedimentary characteristics and reservoir architecture. To discuss the effects of water level fluctuation on sediment characteristics and reservoir architecture of this delta, the Fangniugou section in the east of the Songliao Basin was selected for study. Based on an outcrop investigation of the lacustrine basin river-dominated delta, combining with an analysis of the major and trace chemical elements in the sediments to determine the relative water depth, through architecture bounding surfaces and lithofacies division, sedimentary microfacies recognition and architectural element research, this work illustrated the effects of water level fluctuation on the reservoir architecture and established sedimentary models for the lacustrine basin river-dominated delta under various water level conditions. The results show that there are 8 lithofacies in the Fangniugou section. The fan delta front, which is the main object of this study, develops four sedimentary microfacies that include the underwater distributary channel, river mouth bar, sheet sand and interdistributary bay. The effects of water level fluctuation on different orders geographic architecture elements are respectively reflected in the vertical combination of the composite sand bodies, the plane combination of the single sand bodies, the particle size changes in the vertical of hyperplasia in the single sand body, the coset and lamina. In the case of the sand body development of the petroliferous basin, varying water level conditions and research locations resulted in significant variation in the distribution and combination of the sand bodies in the lacustrine basin.

Paleocommunity Replacements of Benthic Brachiopod in the Middle-Upper Devonian in the Longmenshan Area,Southwestern China:Responses to Sea Level Fluctuations

Twelve paleocommunities dominated by benthic brachiopod are recognized in the Givetian-Frasnian stages of the Devonian in the Longmenshan area, southwestern China, in which two kinds of brachiopod community replacement are classified. One is the abrupt replacement, represented by abrupt alternation between the Leiorhynchus community and Zhonghuacoelia-Striatopugnax community in the Frasnian Tuqiaozi Formation. The other is the gradual one, developed in the Givetian Guanwushan Formation, which had been completed by the shift of the Independatrypa lemma-Uncinulus heterocostellis-Emanuella takwanensis community via the Sinospongophyllum irregulare-Pseudomicroplasma fongi community to the Clathrocoilona spissa-Hexagonaria composite reef community. According to analyses of the paleocommunities, either the abrupt or gradual paleocommunity replacement of the Middle-Upper Devonian in the Longmenshan area is suggested as a response to the 5th-order sea level fluctuation due to the replacements of the paleocommunities in a tracts-system of depositional sequence. It is supposed that changes of paleocommunity diversity, one of the results of paleocommunity replacement, are depended on the range and magnitude of sea level fluctuation, but there is not a linear relationship between them. Furthermore, a suggestion is proposed that the concept of paleocommunity succession seem to be abandoned in the paleocommunity analysis because it almost never be practiced to recover the information of community succession in the geological record at present.

Analysis of the relationship between water level fluctuation and seismicity in the Three Gorges Reservoir(China)

The Three Gorges Reservoir is a good site for the further researches on reservoir induced seismicity due to decades＇ seismic monitoring. After the first water impounding in 2003, seismic activity becomes more frequent than that before water impoundment. In order to quantitatively study, the relationship between the water level fluctuation and earthquakes in TGR, we introduced statistical methods to attain the goal. First of all, we relocated the earthquakes in TGR region with double difference method and divided the earthquakes into 5 clusters with clustering analysis method. Secondly, to examine the impacts of water level fluctuation in different water filling stages on the seismic activity in the 5 clusters, a series of statistical analyses are applied. Pearson correlation results show that only the 175 m water level fluc- tuation has significantly positive impacts on the seismic activity in clusters I, II, III and V with correlation coefficients of 0.44, 0.38, 0.66 and 0.63. Cross-correlation analysis demonstrates that 0, ], 0 and 0 month time delay separately for the clusters I, II, III and V exists. It illustrated the influences of the water loading and pore pressure diffusion on induced earthquakes. Cointegration tests and impulse response analysis denoted that the 175 m water level only had long term and significant effects just on the seismic events in the intersection region of the Fairy Mount Fault and Nine-brook Fault. One standard deviation shock to 175 m water level increased the seismic activity in cluster V for the first 3 months, and then the negative influence was shown. After 7 months, the negative impulse response becomes stable. The long-term effect of the 175 m water impoundment also proved the important role of pore pressure diffusion in RIS with time.

Online dynamic measurement of saturation-capillary pressure relation in sandy medium under water level fluctuation

An online dynamic method based on electrical conductivity probe, tensiometer and datataker was presented to measure saturation-capillary pressure （S-p） relation in water-light nonaqueous phase liquid （LNAPL） two-phase sandy medium under water level fluctuation. Three-electrode electrical conductivity probe （ECP） was used to measure water saturation. Hydrophobic tensiometer was obtained by spraying waterproof material to the ceramic cup of commercially available hydrophilic tensiometer. A couple of hydrophilic tensiometer and hydrophobic tensiometer were used to measure pore water pressure and pore LNAPL pressure of the sandy medium, respectively. All the signals from ECP and tensiometer were collected by a data taker connected with a computer. The results show that this method can finish the measurement of S-R relation of a complete drainage or imbibition process in less than 60 min. It is much more timesaving compared with 10-40 d of traditional methods. Two cycles of water level fluctuation were produced, and four saturation-capillary pressure relations including two stable residual LNAPL saturations of the sandy medium were obtained during in 350 h. The results show that this method has a good durable performance and feasibility in the porous medium with complicated multiphase flow. Although further studies are needed on the signal stability and accuracy drift of the ECP, this online dynamic method can be used successfully in the rapid characterization of a LNAPL migration in porous media.

Modeling of unsteadiness of fluid flows and level fluctuations in thin slab continuous casting moulds

Unsteady fluid flows and level fluctuations in a thin slab continuous casting mould have significant influence on product quality. In this study, the phenomena concerning transient flow features and free surface motions were analyzed by means of the large eddy simulation （LES） software with the smagorinsky SGS model--VisualCast （VCast） II, where the Simpler algorithm on a body-fitted mesh was used to resolve governing equations. A series of water analog experiments on the fluid flow and the surface wave in the moulds of thin slab continuous casting were also performed. The results of fluid regions, middle of vortex and level fluctuation from digital simulations were identical with the results of the water analog experiments.

Water Security-based Hydrological Regime Assessment Method for Lakes with Extreme Seasonal Water Level Fluctuations：A Case Study of Poyang Lake,China

Extreme seasonal water level fluctuations characterize natural floodplain lakes in monsoon regions, which are crucial for ensuring lake water security, including flood prevention water supply and health of aquatic ecosystem. In order to achieve this goal, we established a hydrological regime assessment method based on a set of hydrological indicators for lakes with heavy seasonal water level fluctuations. The results suggest that time-sensitive hydrological indicators and specific time scales for various water security aspects must be considered. We discovered that it is more practical and meaningful to combine the water level classification derived from statistical analyses with characteristic hydrological values linked to water security. The case study of Poyang Lake results show that there are no discernable trends of Poyang Lake water regime status over the last 35 years, and the two periods of poor status are in accordance with climate variation in the lake basin area. Scholars and policy makers should focus on both floods and droughts, which are the main water security problems for Poyang Lake. It is hoped that this multi-scale and multi-element hydrological regime assessment method will provide new guidelines and methods for other international scholars of river and lake water assessment.

Protection and Ecological Restoration of Water Level Fluctuation Zone in the Three Gorges Reservoir

Water level fluctuation zone(hereinafter referred to as "WLFZ") is a transitional ecosystem between terrestrial ecosystem and aquatic ecosystem,and also a key area to control its neighboring terrestrial and aquatic ecosystem. After the Three Gorges Reservoir was put into use,ecological environment of its WLFZ has aroused wide concern from domestic and foreign experts. On the basis of introducing characteristics of WLFZ of the Three Gorges Reservoir,current ecological environment and main problems of this area were analyzed,plant selection and configuration was elaborated as well as the implementation effect of many WLFZ protection and ecological restoration modes. In view of the actual conditions,pertinent suggestions were proposed for WLFZ of the Three Gorges Reservoir,namely classified protection and ecological restoration,enhancing monitoring and assessment of current situation and change tendency,carrying out technical researches and demonstration of WLFZ wetland ecological restoration.

Mechanisms of low-frequency sea level fluctuations in the Hangzhou Bay

-low-frequency sea level fluctuations in the Hangzhou Bay in winter and summer, 1973-1974 are analyzed in this paper. The established multi-spectrum response models effectively identify the different dynamical factors and their contributions to the low-frequency sea level fluctuations inside the bay. The results show that the Ekman transport due to longshore winds is the major mechanism to induce the sea level fluctuations, more important than the frictional effect of local winds. There also exists obviously the influental effect of the free fluctuations of the continental shelf. In addition ,a simple estimation suggests that the remarkable sea level fluctuation of 0. 4 d-1 in the bay is related to the resonance of the Huanghai Sea and the Bohai Sea (taken as a single bay).

Effect of SEN structure on the mold level fluctuation and heat transfer for a medium thin slab caster

It is important to select suitable parameters of a submerged entry nozzle （SEN） for optimizing the flow and temperature patterns in a mold. The effect of SEN design on the mould level stability, meniscus steel flow velocity, and heat transfer of the mold of a medium thin slab caster was studied by means of 1：1 water modeling and industrial testing. The advantages of a 2-port SEN compared with a 3-port SEN are the following： more optimal flow patterns with a lower mold level fluctuation and a lower meniscus steel flow velocity; proper powder consumption without slag bears due to a reasonable liquid powder thickness. The argon flow rate can be reduced and the mold average heat flux and temperature near the edges of the copper plate are reduced. At a casting speed of 2.5 m·min^-1, the mold level fluctuation lies within ＋5 mm. In addition, soft cooling of the steel shell in the mold is realized, which is suitable for casting crack susceptible steel grades.

Characteristic Relationships between Phosphorous Accrual, Ecosystem Aspects and Water Level Fluctuations in Tropical Lakes: Naivasha Ramsar Site, Kenya

Hydrological dynamics affect water levels and thus affecting ecosystem structure and functions. Lake levels in tropical ecosystems affect phosphorous input through runoff from adjacent watersheds. The resultant biological community, water and sediment quality of the lakes due to water level changes is a reflection of the geology of the area and the anthropogenic activities in the watershed. The study conducted between January 2018 and December 2019 was to explore relationships between the phosphorous input and Water Level Fluctuations (WLF) recorded by Water Resource Authority (WRA). Lake water samples were analyzed in the laboratory for phosphorous using molybdenum blue-ascorbic method and recorded using spectrophotometer. Chlorophyll-a was determined by extracting a filtered sample with 15 ml acetone and incubating overnight and thereafter read using a double beam spectrophotometer. Total Suspended Solids (TSS) was determined by filtering 200 ml of a water sample and dried overnight at 105°C. The lowest and highest phosphorous concentrations recorded were 0.2 mg/l and 0.42 mg/l at NST7 and NST2, respectively. Measurements of Chlorophyll-a were 0.32 mg/l and 0.42 mg/l at NST9 and NST2, respectively. Secchi transparency measurements were 32.9 cm at NST3 and 84 cm at NST1. The highest and lowest TSS concentrations were 0.14 mg/l and 0.13 mg/l at NTS1 and NST8, respectively. The hydrodynamic regime in most tropical lakes plays a significant role in the re-reaction of phosphorous that consequently influences productivity. Tropical lakes have extreme lake level fluctuations which accelerate the production process. The influence of water level changes on aquatic productivity is crucial in most tropical lakes and should be taken into consideration when assessing the environmental impacts.

Centrifugal model test on a riverine landslide in the Three Gorges Reservoir induced by rainfall and water level fluctuation

Frequent soil landslide events are recorded in the Three Gorges Reservoir area,China,making it necessary to investigate the failure mode of such riverside landslides.Geotechnical centrifugal test is considered to be the most realistic laboratory model,which can reconstruct the required geo-stress.In this study,the Liangshuijing landslide in the Three Gorgers Reservoir area is selected for a scaled centrifugal model experiment,and a water pump system is employed to retain the rainfall condition.Using the techniques of digital photography and pore water pressure transducers,water level fluctuation is controlled,and multi-physical data are thus obtained,including the pore water pressure,earth pressure,surface displacement and deep displacement.The analysis results indicate that:Three stages were set in the test(waterflooding stage,rainfall stage and drainage stage).Seven transverse cracks with wide of 1–5 mm appeared during the model test,of which 3 cracks at the toe landslide were caused by reservoir water fluctuation,and the cracks at the middle and rear part were caused by rainfall.During rainfall process,the maximum displacement of landslide model reaches 3 cm.And the maximum deformation of the model exceeds 12 cm at the drainage stage.The failure process of the slope model can be divided into four stages:microcracks appearance and propagation stage,thrust-type failure stage,retrogressive failure stage,and holistic failure stage.When the thrust-type zone caused by rainfall was connected or even overlapped with the retrogressive failure zone caused by the drainage,the landslide would start,which displayed a typical composite failure pattern.The failure mode and deformation mechanism under the coupling actions of water level fluctuation and rainfall are revealed in the model test,which could appropriately guide for the analysis and evaluation of riverside landslides.

Water level fluctuations influence microbial communities and mercury methylation in soils in the Three Gorges Reservoir,China

Reservoirs tend to have enhanced methylmercury（MeHg） concentrations compared to natural lakes and rivers, and water level fluctuations can promote MeHg production. Until now, little research has been conducted on the effects of microorganisms in soils for the formation of MeHg during different drying and flooding alternating conditions in the Three Gorges Reservoir（TGR）. This study aimed to understand how water level fluctuations affect soil microbial composition and mercury concentrations, and if such microbial variations are related to Hg methylation. The results showed that MeHg concentrations and the ratios of MeHg to THg（MeHg%） in soils were higher in the seasonally drying and flooding alternating areas（DFAs, 175–155 m） than those in the non-inundated（NIAs, 〉 175 m） and inundated areas（IAs, 〈 145 m）. However, MeHg% in all samples was less than 1%, indicating that the Hg methylation activity in the soils of the TGR was under a low level. 454 highthroughput sequencing of 16 S rRNA gene amplicons showed that soil bacterial abundance and diversity were relatively higher in DFA compared to those in NIA and IA, and microbial community composition varied in these three areas. At the family level, those groups in Deltaproteobacteria and Methanomicrobia that might have many Hg methylators were also showed a higher relative abundance in DFA, which might be the reason for the higher MeHg production in these areas. Overall, our results suggested that seasonally water level fluctuations can enhance the microbial abundance and diversity, as well as MeHg production in the TGR.

NUMERICAL STUDY OF WATER LEVEL FLUCTUATION IN BULL-HORN SURGE CHAMBER IN PIPE SYSTEM DURING WATERHAMMER

The method of characteristics was adopted to analyze water level fluctuationexisting in Bull-Horn surge chamber in reservoir-valve pipe system during waterhammer caused byvalve closure operation. The Finite Difference Method (FDM) based on the method of characteristicswas used to solve numerically the nonlinear two-parameter characteristic equations governingwaterhammer. The finite fixed mesh was applied to obtaining the discrete form of the governingequations and discrete flow-field. The temporal trends of the y -directional flow, water level,velocity of water level and head difference for different heights of water in surge chamber,diameters of cylinder, cutting angles of surge chamber, lengths of horizontal cylinder and lengthsof inclined cylinder were obtained under the condition that the air in surge chamber iscompressible. The conclusions on water level fluctuation in Bull-Horn surge chamber were given basedon the analyses of the obtained transient numerical results. These conclusions can play a guidingrole in designing pipe system and executing surge suppression.

Barotropic current fluctuations coupled with sea level drawdown in Yellow and Bohai Seas

Sub-tidal barotropic current variations coupled with residual sea level fluctuation in the Bohai and Yellow Seas during wintertime are addressed in this study.The temporal evolution and spatial distribution of current fluctuation are investigated using moored acoustic Doppler current profiler data in a three-dimensional numerical model.It is found that a southward current followed by a northward current occurred in the northern Yellow Sea during the fluctuation,concurrent with a significant outflow followed by inflow through the Bohai Strait.The process is consistent from surface to bottom and is coupled with remarkable residual sea level fluctuation.This quasi three-day fluctuation with amplitude 0.2-0.3 m/s leads to 1 m/1.2 m drawdown in the northern Yellow and Bohai Seas,respectively,strongly influencing water exchange between those seas.Because this a prominent feature in the seas,it is necessary to evaluate its effect on fluctuation during winter in future studies,in particular,the northward current during the recovery phase of sea level in the Bohai and Yellow Seas regarding seasonal variation.

Physical modeling of gas-liquid interfacial fluctuation in a thick slab continuous casting mold with argon blowing

Combining with the physical model of level fluctuation in a thick slab continuous casting mold with the cross-section of 1500 mm×280 mm and argon blowing, the rationalities of estimating the level fluctuation by three traditional quantitative approaches were discussed, and the effects of gas flowrate, casting speed, and the immersion depth of submerged entry nozzle （SEN） on the level fluctuation were also investigated. As a result, it seems that three traditional quantitative approaches are not very suitable for estimating the level fluctuation in a mold with argon blowing, so a new approach for estimating level fluctuation in the mold with argon blowing was presented. The experimental results show that the level fluctuation is mainly in the region around the nozzle wall. When the casting speeds are larger than a certain value, there is the escape of large bubbles near the nozzle wall, which causes an obvious increase of level fluctuation. Furthermore, optimal process parameters, viz., the gas flowrate of 6 NL/min, the casting speed of 1.1 m/min, and the immersion depth of 170 mm, are presented to restrain the level fluctuation by a physical model.