Comparison of Long-Term Observed Sediment Trap Efficiency with Empirical Equations for Coralville Reservoir, Iowa

Trapping efficiency (TE) is defined as the percent of particles that are retained within an impoundment. TE can vary from ? 0% indicating no sediment is retained or is lost, to 100% where all the sediment is retained. In this paper a high quality, long-term data set (32?years) was used to demonstrate that annual sediment trap efficiencies for a run of the river impoundment are variable. For water years 1973–2005, annual trap efficiencies for Coralville Reservoir ranged from 5.6 to 95.8%, with a mean of 74.7% and a median of 79.9%. Overall trap efficiency for the entire period was determined to be 80.3% and a detention time of 12.4?days. A comparison of the observed long-term TE was done against different empirical TE equations that are commonly used (Brown, Brune, Churchill, Dendy, Heinemann, & USDA/Summit Co., Water District). The Churchill equation provided the best fit of the empirical trap efficiency equations (TEC = 79.1%); all other empirical TE relationships underestimated the observed trap efficiency with errors ranging from 13.7 to 33.1%. Bathymetric data show that since 1958 the reservoir has lost 11% of its flood storage capacity, and over 62% of its normal pool capacity. For the time studied (1973–2005) the loss of storage is estimated to correspond to 16.9×109?kg of sediment deposited in the reservoir, resulting in an annual sedimentation rate of 5.3×108?kg?year?1.     

Impact of Turbidity Currents on Reservoir Sedimentation

All lakes created on natural rivers are subjected to reservoir sedimentation. The construction of a dam significantly modifies the flow conditions of natural streams inside and downstream of an artificial lake. The sediment concentration is often high during the flood season, and the entering flow shows a greater density than the ambient fluid. Suspended load can therefore be carried along the reservoir bottom to the dam in the form of turbidity currents. This paper presents research results that help to better understand this physical phenomenon, which contributes to reservoir sedimentation. It is based on in situ measurements, a laboratory scale model of turbidity currents and numerical flow simulations. The study of a thousand-year flood in the Luzzone Reservoir in the Swiss Alps using the developed computer model revealed the potential of such a tool. In particular, the impact on the sediment deposits was analyzed. A valuable evaluation of the incidence of such a turbidity flow is presented and its effects are compared to observations. Significant progress has been made in understanding the importance of turbidity currents in reservoir sedimentation.     

Influence of Sediment Layers on Dynamic Behavior of Aged Concrete Dams

The assessment of response of an aged concrete dam is important for the prediction of its behavior during earthquakes, so that remedial measures can be taken at the right time to withstand future earthquakes. The assessment is necessary, since the analyses procedures may become obsolete and the state of the art may change as the time of construction and the structural material may deteriorate due to harsh environmental conditions. At the same time, the sediment will be accumulated at the reservoir bottom on the upstream side of the dam. The process of siltation depends on the reservoir topography and climatic variability, i.e., increased flood frequency and river inflow. The decision of retrofitting or strengthening the aged dam necessitates accurate analysis of the same in the presence of accumulated sediment. In this paper, an approach to include the time-dependent degradation of concrete owing to environmental factors and mechanical loading in terms of isotropic degradation index is presented. The absorption of pressure waves at the bottom of the reservoir due to the presence of sediments has been incorporated in the hydrodynamic pressure equation. The response of an aged concrete dam in the presence of sediment layers under seismic excitation is studied. The outcomes show the efficiency of the proposed algorithm.     

Case Study of Fluvial Modeling of River Responses to Dam Removal

A plan was made to remove Matilija Dam on the Ventura River. With dam removal, the delta in the reservoir and the downstream channel were expected to undergo major changes in morphology. The FLUVIAL-12 model was employed to simulate reservoir and river channel responses after dam removal. As a first step, the model was calibrated using the Ventura River data to establish its validity. In calibration, the model was used to simulate the fluvial processes starting from the time of dam completion. The simulated sediment deposition above the Matilija Dam matches closely with the deposits measured by the U.S. Bureau of Reclamation. A large amount of sediment was stored in the reservoir; some of the stored sediment would be transported downstream after dam removal. An important consequence of dam removal is the major increase of sediment release to the river channel downstream. The sediment supply to the downstream reach is not only from the stored sediment in the reservoir but also from natural sediment inflow from the upstream watershed. Therefore, sediment supply to the downstream reach will exceed the natural sediment flow before the dam presence. This situation tends to overload the downstream reach with sediment, resulting in excessive deposition. The amount of sediment release from the area above the removed dam is closely related to the changes in reservoir morphology. It is necessary to model changes in the channel bed profile and channel width during erosion in order to determine the amount of sediment removal. The amount of sediment release may not be simulated using an erodible-bed model but it may be determined using an erodible boundary model.     

Discharge and Suspended Sediment Transport during Deconstruction of a Low-Head Dam

In March of 2003, the 43?m wide, 2.2?m high St. Johns Dam (Sandusky River, Ohio) was breached to lower the water level in the reservoir. In November of the same year, the dam was removed in an effort to restore aquatic habitat and connectivity in the river. During both the breach and the dam removal, high resolution time series of discharge and suspended sediment concentrations were monitored 200?m downstream of the dam. Discharge and suspended sediment during the breach were not discernible from background values. In contrast, the dam removal resulted in a peak suspended sediment concentration of 59?mg/L and a peak discharge of 33.5?m3/s, which returned to background levels of 19?mg/L and 1.5?m3/s, respectively, approximately 8?h after the removal. The floodwave during the removal attenuated by 50% at the City of Fremont, 53?km downstream, illustrating the diffusive nature of the channel and the limited risk of flooding downstream. Levels of suspended sediment and discharge during the removal were comparable to subsequent discharge events. Spatial distributions of turbidity in and upstream of the dam pool and archived turbidity data from the City of Tiffin, 13?km downstream of the dam, suggest that sediments stored in the impoundment did not statistically enhance turbidity up to 2 years after the removal. Generally, the removal had a minor impact on water quality and posed no risk to public safety or to downstream aquatic habitats.     

Life of Maithon Reservoir on Ground of Sedimentation: Case Study in India

This case study discusses the life of the Maithon Reservoir studied based upon the past reservoir sedimentation trends and downstream demands for which the reservoir was built, where increased or projected demands were not considered during the study. Various studies have been done to observe declining storage in different zones of the reservoir, including reliability of the conservation storage, rise of reservoir bed level, reduction of reservoir trap efficiency, etc., at different projected years. An attempt has also been made to discuss the full life of the reservoir and to provide a short discussion of different strategies for its prolonged life because sediment is filling the reservoir much faster than its designed life. An additional life of 58?years for the Maithon Reservoir may be obtained if the Balpahari Reservoir is constructed as a siltation trap at just the upstream of the Maithon Reservoir within the year 2005. Actually, this case study provides a guideline for dealing with a practical sedimentation problem along with the serviceability of a reservoir based upon Murthy’s recommendations.     

Sediment Discharge from a Storm-Water Retention Pond

A small storm-water retention pond is primarily designed to reduce the peak rate of surface runoff. From a water quality standpoint, that same pond may be irregular in shape and trap suspended sediment carried by the surface runoff generated upstream of the site. Considering different pond inlet locations, the writer’s numerical model is used to investigate the change in peak concentration of sediment discharge at the pond outlet. It has been found that the various hydraulic conditions can have a significant impact on sediment discharge. Three different cases are presented to show the flexibility of modeling changes in boundary conditions. The results may help designers evaluate sediment discharge to determine the most effective pond inlet locations.     

大口辐射井在尾矿库堆积坝排渗中的应用

In order to solve the problem that the saturation line of the dam body is shallow in the safety inspection of Dexing Copper Mine tailing dam of Jiangxi Copper Co., Ltd., and ensure the stability of the dam, the reasons for the shallow buried depth of the saturation line of the dam body are analyzed firstly. Then, considering the characteristics of different drainage methods of the tailings pond, combined with the actual situation of the No.2 tailings pond of Dexing Copper Mine, the addition of large radial wells and water is proposed through the establishment of seepage finite element calculation model, it is concluded that after adding large radial well and horizontal drainage layer, the buried depth of saturation line of tailings pond is obviously reduced, the influence range of large radial well is 128~184m, the elevation phreatic line is 5 ~ 12m lower than the current situation, and the average buried depth of phreatic line is 15m, which meets the design requirements under normal working conditions, the saturation line of the dam body is controlled to be 15m deep, which effectively ensures the stability of the dam body.     

Experiments on Deposition Behavior of Fine Sediment in a Reservoir

The deposition behavior of fine sediment is an important phenomenon, and yet it is unclear to engineers concerned about reservoir sedimentation. Laboratory experiments were conducted to produce both quasi-homogeneous flow and a turbidity current region divided by a plunge section. Silica powder (a noncohesive sediment) and kaolin (a cohesive sediment) were used as the suspended material. Because the effective gravitational force is the primary driving force for velocity in turbidity currents, the velocity profile was closely related to the concentration profile. The deposition rate of noncohesive coarser particles exponentially decays along the flow path. Most of the coarser particles were deposited in the quasi-homogeneous flow region or within a small distance downstream of the plunge section. The plunge did not carry those coarser particles further downstream. Deposition in the region of the turbidity current was found mainly by cohesive particles. Hydraulic sorting exists in the quasi-homogeneous flow region for noncohesive coarser particles, but becomes less significant in the downstream portion with deposition rates becoming mildly decayed. For fine cohesive particles, hydraulic sorting for the deposited gradation is not significant.     

气驱排渗技术及其在膏体尾矿筑坝工程的应用

果郎沟尾矿库为甲玛铜多金属矿二期工程配套尾矿库,采用初期坝+膏体上游法堆坝形式,实际运行过程中存在尾砂渗透系数低、不固结,且坝体浸润线埋深仅10 m左右等问题。华泰龙矿业公司采用气驱排渗技术,在坝体均匀布设特殊结构的竖直和水平排渗管,采用高压气驱和重力自流的联合排渗方式,大大提高了坝体排渗效率,浸润线埋深快速降低至20 m左右,提高了坝体稳定性。气驱排渗技术有效解决了果郎沟尾矿库子坝排渗固结程度低的难题,同时为膏体尾矿筑坝方式及排渗技术提供了参考依据。     

赤泥吸收矿化CO2技术研究

赤泥是氧化铝生产过程中产生的碱性工业固废。以赤泥为主要原料制备CO2吸收矿化材料,分析了吸收矿化反应过程、反应前后赤泥浆液中Na+转移特性及pH与吸收矿化效率的关系。结果表明,赤泥浆液吸收矿化CO2后,赤泥出现一定量的钙霞石和方解石、比表面积增加至12.0 m2/g。同时,部分Na+从赤泥转入溶液中,溶液中钠离子升高至2.81 g/L。采用赤泥吸收矿化CO2效率为27%以上,矿化CO2后产生的赤泥pH稳定维持在7.5左右。     

基于模糊多元联系度模型的尾矿库综合安全评价

为准确评价尾矿库的安全等级，以黄金洞尾矿库为例，分析影响尾矿库安全的各因素之间的关系，综合运用模糊多元联系度理论与层次分析法（AHP），建立了包含5个影响因素和26个影响因子的尾矿库综合安全评价模型。由AHP得出各项主、客观指标的权重系数，引入模糊多元联系度理论，综合考虑确定性与不确定性因素，处理综合集成问题，构造隶属函数量化指标的实测值。结果表明：黄金洞尾矿库安全等级为Ⅱ级，尾矿库处于较稳定状态。经比较不确定性因素大小，得出尾矿排放（B₃）>尾矿坝（B₂）>安全管理（B₁）>尾矿输送与回水（B₅）>排洪系统（B₄），说明尾矿排放指标的不确定性因素最大，需对尾矿排放加强管理。该模型得到的评价结果与实际结果相吻合，为尾矿库安全性评价提供了一种可行的方法。     

Case Study: Delayed Sedimentation Response to Inflow and Operations at Sanmenxia Dam

This paper presents a study on the reservoir sedimentation processes in response to changes in incoming flow at the upstream and changes in the pool level at the downstream for Sanmenxia Reservoir, which is located on the middle reach of the Yellow River in China and has experienced serious sedimentation problems even since its impoundment in 1960. The hysteresis effect in reservoir sedimentation was used as the basis for analysis and its behavior was fully investigated throughout this study. The research found that the rise in the elevation of Tongguan, which is located in the backwater region at a distance of 113.5?km upstream of the Sanmenxia Dam, had a time delay of about 2?years compared with the sediment deposition in the reservoir area downstream of Tongguan. Moreover the accumulated sediment deposition in the reservoir area was closely related not only to the current year’s flow and dam operational conditions, but also to the preceding 3–4?years’ flow and dam operational conditions. Likewise the variation of Tongguan’s elevation was a function of 6?years’ linearly superimposed runoff, and the channel bed slope in the vicinity of Tongguan was determined by a moving average pool level over a 7?year period. The research results are of practical importance in particular for optimizing the operation of Sanmenxia Dam, and the finding of the hysteresis phenomenon in the sedimentation process of the reservoir is of merit to the advancement of sedimentation science.     

论国内氧化铝赤泥库的建设模式

文章分析国内氧化铝赤泥库的性质,赤泥库的历史状况和当前建设模式,对赤泥库的建设提出了合理性意见并对建设模式的发展作出了展望,希望能够为今后的氧化铝赤泥库建设提供一定的参考。     

Avian diving, respiratory physiology and the marginal value theorem

We studied the effect of pressure up to 300 bar on the catalytic efficiency of subtilisin Carlsberg suspended in compressed propane, near-critical ethane, near-critical carbon dioxide and tert-amyl alcohol, at constant temperature and fixed enzyme hydration. Increasing pressure lowered the catalytic efficiency of the enzyme in all the solvents, resulting in positive activation volumes, delta V#. The delta V# values in compressed propane and in tert-amyl alcohol were similar and larger in magnitude than the value reported in the literature for the same reaction in an aqueous buffer, although within the range of typical delta V# values in aqueous media. In the near-critical fluids, the delta V# were much larger, e.g., an increase in pressure of only 200 bar causing a sixfold decrease in the catalytic efficiency of subtilisin in carbon dioxide. These data should reflect the proximity of ethane and carbon dioxide to the critical point, and the resulting condensation of solvent molecules about the solutes, yielding negative solute partial molar volumes.     

Control of Turbidity Currents in Reservoirs by Solid and Permeable Obstacles

Turbidity currents are often the main process for the transport and deposition of the sediments in narrow, alpine reservoirs. These underwater avalanches with high concentration of suspended sediments follow the thalweg of the lake to the deepest area near the dam, where the sediments can affect the operation of the bottom outlet and the intake structures. To control the sedimentation within the reservoir, the effects of solid and permeable obstacles on the turbidity current were investigated with physical experiments and numerical simulations. In the physical experiments, the velocity distributions as well as the spatial and temporal evolution of the deposits were measured. The investigated measures were also simulated by means of a two-dimensional numerical model, based on the flow solver CFX-4.4. The investigations showed that turbidity currents can be influenced effectively by properly designed constructive measures. Based on the results of the physical experiments and numerical simulations, some design recommendations for solid and permeable obstacles are proposed.     

Modeling Resuspension in a Dynamic Water Supply Reservoir

Enhancements to the two-dimensional lake and reservoir water quality model W2Tn to simulate the effects of currents and waves on sediment resuspension and turbidity are described. Bed stress attributable to currents was computed by the hydrothermal component of W2Tn, whereas a surface wave component was added to W2Tn to determine bed stress owing to waves. Resuspension flux is computed from bed stress and is included as a source of turbidity to the water column. The model is tested through application to Schoharie Reservoir, a drinking water supply that experiences episodes of elevated turbidity caused by runoff events and exacerbated by drawdown. Model predictions of bed stress attributed to currents are validated by using measurements obtained from acoustic Doppler instrumentation. The surface wave component of the model is established on a framework that has been previously validated for Schoharie Reservoir. Testing of the enhanced turbidity component of W2Tn was completed for a 3.5-year period of historical observations, which included a number of runoff events covering a range of severity and variations in reservoir drawdown. The enhanced model performed well in simulating observed conditions in the water column. The resuspension mechanism made a significant contribution to the predicted turbidity during periods of reservoir drawdown and during a severe runoff event. The model also performed well in simulating the observed turbidity of the drinking water withdrawal. Resuspension of particles contributing to turbidity was largely attributable to reservoir currents with surface wave-induced resuspension playing a smaller role. The potential application of this model to other water bodies and water quality issues is discussed.     

新型高密度沉淀池在唐钢的应用

利用新型高密度沉淀池对钢铁联合企业废水进行处理,控制最佳条件:投加熟石灰控制p H值10.0~11.0,聚合硫酸铁用量20~50 mg/L(有效浓度9%),有机高分子絮凝剂聚丙烯酰胺用量0.2~0.5mg/L。经混凝沉淀后,出水浊度可稳定控制在0.5 NTU以下,有效降低了后续V形滤池及双膜法的运行压力,高密度沉淀池排泥浓度为3%~15%,可直接进入板框压滤机脱水成为含水55%的泥饼。     

某尾矿库坝体稳定性分析

针对某尾矿库的现状,在现场调查的基础上,分析了尾矿初期坝和堆积坝坝体的组成结构,开展了尾矿工程特性研究和不同情况下的坝体稳定性研究,并探讨了坝体的灾害防治措施。研究结果表明：从放矿口至库内尾矿粒径由大变小,堆积尾矿由东向西整体上有西粗东细的特征;选取瑞典圆弧法、毕肖普法等对上游法尾矿库堆积坝稳定性进行分析比较,运用数值分析方法计算各种情况下尾矿坝的安全系数均大于1.25。为了保证坝体安全系数满足规范要求,必须保证坝体排渗设施安全有效运行,及时降低坝体浸润线高度。基于安全考虑,可依靠增加坝体自重和降低库内水位来减小坝体的滑坡风险。该研究成果能为尾矿库的灾害防治提供理论依据。     

斜管沉淀池自动排泥系统改造

沉淀池的排泥对其运行效果有着直接、重要的影响。PLC控制的自动排泥系统解决了人工排泥的不及时、不彻底问题。介绍了马钢供排水厂改造斜管沉淀池自动排泥系统的经验。