STABILITY OF DENSITY STRATIFIED FLOW IN THE BOUNDARY LAYER

1. INTRODUCTION The influence of vertical density variations o the stability of flow past a flat horizontal wall, is in sense related to the case of centrifugal forces actin on a homogeneous fluid flowing along a curved wal When the arrangement is stable, the densit decreases upward, , whereas it becomes unstabl when the variation in density is reversed. In the cas of flow with stable density stratification, turbulen mixing in the vertical direction is impeded becaus heavier particles must…     

Assignment of safety criteria to the stability of earthen slopes of retaining structures

The problem of determining criterial values of K1 and K2 is examined for the enclosing dike of an intake channel as a function of the position of the depression curve and a seismic effect. The requirements of regulatory documents are analyzed. Suggestions are made for determination of the criterial value of K2 with respect to the slope stability of artificial embankments.     

混流式水轮机上冠空腔结构内部流场及单向流固耦合分析

为研究上冠空腔结构对混流式水轮机水力性能与结构特性的影响,建立了不含上冠空腔结构（No UpperCrown Cavity Structure,NUCCS）和含上冠空腔结构（Upper Crown Cavity Structure,UCCS）的两种混流式水轮机全流道几何模型,基于SST湍流模型、顺序耦合法、预应力模态分析,对NUCCS与UCCS的两种混流式水轮机展开数值模拟和单向瞬态流固耦合计算,发现泄水锥处上冠空腔结构可减少转轮内部二次流动损失。在0.8Q_d、Q_d和1.2Q_d的3种流量工况点,分别对混流式水轮机展开瞬态流固耦合计算,对比研究转轮结构的应力应变特性。研究发现含UCCS时,转轮等效应力和变形量均有减小。在小流量0.8Q_d工况点,转轮结构等效应力及应变较小,其最大变形点位于下环附近。在设计流量Q_d和大流量1.2Q_d工况点,转轮等效应力及应变较大,其最大变形点位于上冠附近。在NUCCS与UCCS的转轮进行预应力模态分析时,发现上冠空腔结构对转轮的模态影响很小。本文研究内容可为提升混流式水轮机设计水平提供一定参考依据。     

Design of earthen vegetated open channels

Modified formulas for Manning's equation are developed for use in the design of earthen open channels with submerged aquatic weeds. The proposed relations have their basis in field and experimental data. A multiple regression analysis was used to develop a relationship between the mean velocity, hydraulic radius, and water surface slope. The new formulas are dependent on the distribution of weeds along the channel's wetted perimeter and the percentage of vegetation density with respect to the cross-section area of the waterway.Notation A cross-section area - A _w area of weeds - B ₁ top width of channel flow - g acceleration of gravity - h height of roughness element - n Manning's coefficient - Q discharge of flow - R hydraulic radius - S water surface slope - S ₀ bed surface slope - V mean flow velocity     

考虑地表反照率时域重建的海河流域蒸散发模拟研究

地表反照率（a_c）是计算辐射收支分配的重要参数,其精度对实现大尺度地表蒸散发（ET）的准确模拟有重要意义,在ET模拟中常用线性插值法来获取时间连续的a_c数据,但其a_c重建过程的机理性不足。本研究利用时域重建方法获取a_c的逐日数据,利用Penman-Monteith-Leuning（PML）模型对海河流域ET进行了模拟,并与传统的基于线性插值计算a_c的方法进行对比,分析了不同a_c输入对ET模拟结果的影响。结果表明：（1）采用时域重建方法得到的a_c进行ET模拟时,在海河流域与2008、2010及2018年4个涡度相关数据的相关系数均在0.53以上,相关性较好;（2）海河流域2018年的a_c呈现出北高南低的特征,同时夏季和冬季的高值区相对较小;（3）望都站的示例分析表明,与采用线性插值得到的a_c方案相比,对a_c进行时域重建后进一步降低了ET模拟值的均方根误差和偏离度,可为提高蒸散发精度提供借鉴。     

萍乡市城市地表径流污染物浓度变化特征分析及数值模拟

以海绵城市建设试点城市萍乡市地表径流污染物（以SS和TP为代表）浓度变化特征与预测模型适应性为研究对象,根据两场次的降雨资料及实测径流污染物浓度数据,确定所建地表径流污染物浓度变化预测模型Sartor-Boyd和p/r模型的参数,并模拟和分析了地表径流污染物浓度变化过程。结果表明：萍乡市地表径流污染物（SS和TP）浓度受初始冲刷效应的影响,降雨过程前期随雨强的峰值而达到最大,降雨过程后期污染物浓度受雨强的峰值波动影响较小;受模型参数的影响,Sartor-Boyd模型模拟值的统计学指标RPD、R²、NSE均小于p/r模型的相应指标,p/r模型对萍乡市降雨地表径流污染物排放规律的预测精度较好,模型可信度较高。结合萍乡市地区降雨状况建立的p/r数学模型可为该区域海绵城市建设过程中地表径流污染物浓度的预测及管理提供参考。     

清澜港红树林浮游植物群落结构及水质对应分析

为了认清热带地区红树林中浮游植物群落结构和其关键水质影响因子,分别于2015年11月和2016年3月和8月在海南清澜港红树林进行样品采集,进行藻类鉴定和水质分析。结果表明:调查期间浮游植物7门,74属(种)。蓝藻门13属(种),硅藻门35属(种),绿藻门13属(种),隐藻门4属(种),裸藻门3属(种),甲藻门3属(种),金藻门3属(种)。八门湾优势种为硅藻门角毛藻(Chaetoceros)和硅藻门小环藻(Cyclotella sp.);红树林潮间带优势种为蓝藻门假鱼腥藻(Pseudoanabaena sp.)和甲藻门多甲藻(Peridinium);养殖水优势种为蓝藻门微囊藻(Microcystis)和隐藻门蓝隐藻(Chroomonas placiodea)。养殖水浮游植物密度最高,其次是八门湾和潮间带。除2016年3月份外,生物多样性指数均值由大到小顺序为:潮间带,八门湾,养殖水。2015年11月时氮为藻类生长限制因素,而2016年3月和8月时磷为大部水体限制因素。藻类与氮磷营养盐及金属离子密切相关,季节变化影响不明显。     

The role of soil characteristics in the succession of two herbaceous lianas in a modified river floodplain

The Tamagawa floodplain of Japan experienced a series of changes in the structure of its plant community after 1960. Today, two dominant lianas – Pueraria lobata and Sicyos angulatus – have colonized the area and are competing for space. This study explores their competitive abilities in relation to soil factors and flooding disturbance downstream of the Tama River. Several colonies of these species were selected in three spots of the Tamagawa floodplain having different soil characteristics and flooding frequencies. Our results revealed that S. angulatus can only grow on fine sediment, whereas P. lobata can grow on soil with a wide range of particle sizes. Soil moisture and nitrogen requirements are higher for S. angulatus. S. angulatus grows only on fine sediment for two reasons: first, fine sediment stores a higher concentration of nitrogen and moisture; second, S. angulatus has a very shallow root system. P. lobata has an extensive root system with nodules, with which it can thrive on coarse and relatively dry soil with lower nitrogen. However, P. lobata requires higher soil phosphorus than S. angulatus does. The earlier patchy colonization of S. angulatus on the Tamagawa floodplain was provoked by flooding, when the perennial Miscanthus sacchariflorus and other species trapped fine sediments. Gradually, sediments became finer and nutrient‐rich due to vegetative decomposition, and S. angulatus invaded the area. The soil at that time was not deep enough for the root system of P. lobata. Subsequently, P. lobata outcompeted S. angulatus on the various types of soil that developed. Severe washing of fine substrates by floodwaters makes the area unsuitable for S. angulatus, whereas P. lobata continues to thrive. Copyright © 2010 John Wiley & Sons, Ltd.     

Fusibility and sintering characteristics of ash

The temperature characteristics of ash fusibility are studied for a wide range of bituminous and brown coals, lignites, and shales with ratios R _B/A of their alkaline and acid components between 0.03 and 4. Acritical value of R _B/A is found at which the fusion temperatures are minimal. The sintering properties of the ashes are determined by measuring the force required to fracture a cylindrical sample. It is found that the strength of the samples increases sharply at certain temperatures. The alkali metal content of the ashes has a strong effect on their sintering characteristics.     

Bifurcation behavior of laminar flows of a boundary layer problem

This paper presents a theoretical analysis on the bifurcation behavior of solutions to a nonlinear equation f‴ − ff″ = 0 with boundary conditions: f(0) = C, f′(0) = ξ and f′(∞) = 1 where ξ and C are parameters. It shows that if ξ ≥ 0 including the case ξ ≥ 1, then for any C the boundary value problem has at most one solution. However, for any ξ < 0, there exist some C < 0 such that the boundary value problem admits at least two solutions.

     

Bi-site Analysis of Meteorological Drought Duration: Theoretical Modeling and Application

Droughts are regional incidents that threat the environment and limit most of the socio-economic activities. Given the dry and wet state sequences for two sites, X_t^{( 1 )}X_t^{\left( 1 \right)} and X_t^{( 2 )}X_t^{\left( 2 \right)} , this paper presents a procedure to reduce the two sequences X_t^{( 1 )}X_t^{\left( 1 \right)} and X_t^{( 2 )}X_t^{\left( 2 \right)} to one sequence Z _t for the purpose of simplifying the analysis of drought duration at two sites jointly. Theoretical models to evaluate the expected value and the variance of the process Z _t and the occurrence probability of the dry state at two sites jointly are presented and verified using simulation experiments. Historical data for the period 1939–2005 and generated rainy season precipitation data for two gauging sites in Central Jordan, namely Amman Airport and Madaba, is used in the present study to investigate the occurrence of droughts. The joint analysis of drought duration obtained using the historical precipitation at the two sites appears to be inconsistent especially for droughts of duration longer than 3 years. On the other hand, the joint analysis of drought duration obtained theoretically by employing the characteristics of the process Z _t are found to match well with the more reliable drought statistics obtained empirically by analyzing the long generated precipitation. Considering 25 years planning horizon, droughts of 1, 2, and 3 years duration are the most frequent droughts in the region of Central Jordan. The return period of such regional droughts ranges from 8–30 years.     

Effects of river regulation on the lower Ebro river (NE Spain)

The regulation of the Ebro River in the 1960s has changed the discharge pattern: spring floods have been reduced and, as the reservoirs are used for hydroelectrical purposes, discharge varies daily. The last 50 km of the river have been studied for two years (1986 and 1987). Our main purpose was to establish the particulate organic and inorganic transport of the river and its seasonal changes. Particulate material was sampled in surface and deep waters. Water conductivity ranges between 0.9 and 53 mS, and anoxia is common in summer situations. Particulate C ranges between 1 and 3 mg l^?1 with higher values in summer; particulate N is very similar along the year with values between 0.1 and 0.5 mg l^?1. Effects of regulation seem to be important in supplying very high nutrient content to algae and producing a high biomass and production in the lower part of the river, especially in summer. Diatoms and Chlorophyta are the most abundant groups. Phosphorus is higher than 5 μmol l^?1, with lower values in summer. Most of particulate material is very fine (between 0.45 and 50 μm). The high biomass also explains the presence of abundant filter-feeders, such as Hydropsyche and Ephoron virgo. In some parts, where light reaches the bottom, stones and boulders are covered by Cladophora. In this case, grazers such as the gastropods Melanopsis and Theodoxus are abundant.     

Annual redd counts across two decades are indicators of changing migratory bull trout population sizes in two proximate Montana creeks

Redd counts are the most widely used method for bull trout (Salvelinus confluentus Suckley) population monitoring. Redd counts are an assumed indicator of population size (N), particularly for female spawners, but previous studies rarely considered the measurement uncertainty of N. The present study of two proximate, migratory bull trout populations across two decades examined statistical correlations between annual redd counts and concurrent N (predominantly fish ages 3–7) that included measurement uncertainty. Results showed that redd counts explained about one-third of the concurrent N variation and, in one case, portended N 7 years later. But changing spawning distributions across years, as likewise shown here and as a probable effect of ongoing climate change, can confound the use of fixed index reaches for redd counts. Instead, abundance monitoring based on redd counts should be over a bull trout population's or metapopulation's entire spatial extent and have counts in all potential spawning areas. Such total-annual redd counts may be the most cost-effective and precise means of bull trout population monitoring.     

The effects of dreissenid mussels on the survival and condition of burrowing mayflies (Hexagenia spp.) in western Lake Erie

Burrowing mayflies (Hexagenia limbata and H. rigida) are once again prominent members of the benthic community in western Lake Erie. However, this community is now dominated by dreissenid mussels. We conducted a laboratory experiment and field sampling to investigate whether survival and condition of Hexagenia were affected by the presence, density, and quality of dreissenid mussels. In a laboratory experiment, Hexagenia survival was higher in microcosms without dreissenid mussels. We also found Hexagenia density to be higher at field sites with low dreissenid density, suggesting that Hexagenia survival is higher in these areas as well. In microcosm treatments with low dreissenid density, Hexagenia survival was higher in treatments with live dreissenids than in treatments containing only dreissenid shells. These findings suggest that while dreissenid shells degrade the quality of soft sediments for Hexagenia, some of the negative effect is offset by the presence of live dreissenids. The positive effect of live dreissenids is likely due to additional food resources made available to Hexagenia by the filtering activity of dreissenids. Neither dreissenid density nor shell “type” (shells alone or live dreissenids in shells) had an effect on Hexagenia condition. Thus, the interactions between these dominant benthic invertebrates are complex. Recovery of Hexagenia populations in western Lake Erie is likely affected by both changing environmental conditions due to anthropogenic activities and the introduction of exotic species into the benthic community. The results are likely to be continued instability of the benthic food web and unpredictable consequences for human utilization of this ecosystem.     

Comparison of macrobenthos in braided and channelized sectors of the Drôme River,France

The influence of braided pattern on macrobenthic communities was studied in the Lower Drǒme River (France). The qualitative differences between embanked and braided sections are weak. The sessile species (for example Psychomyia pusilla) are more frequent in the embanked section whereas the drifting species (for example Baetis fuscatus) are more frequent in the braided section. The density of macroinvertebrates in the latter, especially in the secondary channels, is higher than in the embanked section, but the diversity remains low because the location of the channels changes at each extreme flood.     

Physico-mechanical characteristics and mechanism of concrete leaching in cracked zone of reinforced-concrete penstock linings at the Sayano-Shushenskaya HPP

Results are presented for investigations of strength and deformation characteristics of the monolithic concrete and concrete in the cracked zone of the linings, the temperature_moisture-content regime of the linings, and the condition of the reinforcement. The causes and mechanism of leaching of cement stone from the concrete in the cracked zones are outlined; and, recommendations are given for diminishing the negative effect of the leaching. Translated from Gidrotekhnicheskoe Stroitel‘stvo, No. 7, July 2008, pp. 17–25.     

Role of Daphnia in the decomposition of organic matter in the surface layer of Lake Biwa

To examine the role of Daphnia in the decomposition and elimination of organic carbon at the surface layer, organic matter from Lake Biwa was incubated with and without Daphnia at 20°C in the dark for 15 days in May, July and October. In all of the experiments, total organic carbon decreased during the incubation, regardless of treatment; however, the net effect of Daphnia on this decrease differed among experiments. Daphnia stimulated the decrease in particulate organic carbon in two out of three experiments. Bacterial abundance was higher in treatments with Daphnia than in treatments without Daphnia in all experiments. Higher bacterial abundance in treatments with Daphnia could not be explained fully by zooplankton grazing effects on phagotrophic protozoans, rather Daphnia seemed to stimulate bacterial growth by supplying substrates for that growth. The results of the present study suggest that Daphnia reduces sinking flux, not only by direct grazing, but also by the channelling of particulate organic carbon into dissolved forms that are then available for bacterial growth.     

Invasiveness screening of non‐native fishes for the middle reach of the Yarlung Zangbo River,Tibetan Plateau,China

The aim of this study was to identify potentially invasive non‐native freshwater fishes in the middle reach of the Yarlung Zangbo River, Tibetan Plateau (China), using the Aquatic Species Invasiveness Screening Kit (AS‐ISK), as decision‐support tool. Based on independent evaluations of 24 non‐native freshwater fishes, receiver operating curve analysis identified a threshold score of ≥29 for distinguishing species likely to pose a high risk of becoming invasive from species likely to pose low‐to‐medium risk (<29) in the risk assessment area. Nine species were categorized as “high risk”: goldfish Carassius auratus, topmouth gudgeon Pseudorasbora parva, brook trout Salvelinus fontinalis, Oriental weatherfish (a.k.a. dojo gudgeon) Misgurnus anguillicaudatus, Siberian taimen Hucho taimen, common carp Cyprinus carpio, peled Coregonus peled, western mosquitofish Gambusia affinis, and Chinese rice fish Oryzias sinensis. The three lowest scoring species were Arctic cisco Coregonus autumnalis, Wuchang bream Megalobrama amblycephala, and Chinese ice fish Neosalanx taihuensis, which are unlikely to be invasive because they are unable to complete their life cycle in the risk assessment area. Climate change assessments scores increased or remained the same for warm‐water species and decreased for coldwater species. This study was the first application of AS‐ISK in western China, and the results suggest that AS‐ISK is a useful and valid tool for identifying potentially invasive risk aquatic species in China.     

考虑气象因子不确定性的参考作物蒸散量预报方法

参考作物蒸散量(ET0)的准确预测预报对于制定作物灌溉制度与实时灌溉调度具有重要意义,然而气象因子的不确定性极大的影响着ET0的预测精度.因此本研究采用马尔科夫蒙特卡罗模拟与自适应采样算法相结合的方法(AM-MCMC)对气象因子的不确定性进行修正,以气象站实测ET0作为标准值,利用径向基神经网络(RBF)模型建立气象因...     

Vegetation Buffer Strips Design Using an Optimization Approach for Non-Point Source Pollutant Control of an Agricultural Watershed

Management of agriculture-induced water quality problems requires an integrated approach involving selection of the most suitable and economical Best Management Practices (BMP). Vegetation Buffer Strips (VBS), one of the commonly used off-field structural BMPs, when designed and placed correctly, can significantly improve the water quality. However, VBS takes up agricultural land used for crop production and the implementation/maintenance costs are of concern. Currently, the standards for design of VBS (location and width) are normally set on field study basis, and they do not involve science-based approach to guarantee their efficiency under regional variations, geological and economical conditions. The present study proposes a new approach which integrates computational modeling of watershed processes, fluvial processes and modern heuristic optimization techniques to design a cost effective VBSs in a watershed. The watershed model AnnAGNPS (Annual AGricultural Non-Point Source Pollution Model) and channel network model CCHE1D (Center for Computational Hydroscience and Engineering One(1) Dimensional Model) are linked together to simulate the sediment/pollutant transport processes. Based on the computational results, a multi-objective function is set up, which aims to minimize soil losses, nutrient concentrations as well as total costs associated with installation and maintenance of VBS, while the production profits from agriculture production are being maximized. The solution procedure involves the use of iterative Tabu Search (TS) algorithm to flip VBS design parameters (switching from one alternative to another). The search for the optimal solution follows an iterative procedure. An illustrative case study of USDA’s Goodwin Creek experimental watershed located in Northern Mississippi is used to demonstrate the capabilities of the proposed approach. The results show that the optimized design of VBS using an integrated approach at the watershed level can provide efficient and cost-effective conservation of the environmental quality by taking into account productivity and profitability.