持续大流量过程对黄河内蒙古河段河道塑形能力的分析与思考

2018年伏秋汛期黄河流域上游持续来水,为保证2108-2019年度黄河流域凌汛期安全,黄河流域重点水库进行了大流量持续下泄。以2018年9月的实际数据为基准,通过对重点水库实际日均出入库调度情况,内蒙古河段的重点水文站实际日均流量过程和三个年份汛期大断面套绘成果对比分析研究,可以得出水库大流量持续下泄对内蒙古河段河道塑形能力起到了关键性作用,有效的提高了主槽过流能力,河段最小平滩流量得到一定的恢复,对下一步研究黄河流域河道过流能力提供了有利的数据支撑和参考价值。     

Coanda effect in coastal flows

In the present paper some numerical simulations and experiments were carried out to study jet-wall interaction in shallow waters. Namely, modifications of the hydrodynamic field concerning the interaction of river run-off with a shallow coastal water body, due to the presence of marine structures, were investigated. Stratification effects due to salinity and temperature were neglected, and the interest was focused on barotropic features (Coanda effect). The numerical analysis was carried out by means of shallow water equations, numerically solved by finite difference, and the present method was validated by means of a typical simple-shaped test case. The experiments were carried out in a shallow water tank, flow visualizations were performed, and the velocity field was obtained by PIV. The main features of jet-wall interaction flow were investigated in simple-shaped geometries, and applications were shown for two practical cases: Pescara channel harbour (Adriatic Sea, Italy) and the proposed design of Latina harbour (Tyrrhenian Sea, Italy).     

Slow quasigeostrophic unstable modes of a lens vortex in a continuously stratified flow

This work addresses the linear dynamics underlying the formation of density interfaces at the periphery of energetic vortices, well outside the vortex core, both in the radial and axial directions. We compute numerically the unstable modes of an anticyclonic Gaussian vortex lens in a continuously stratified rotating fluid. The most unstable mode is a slow mode, associated with a critical layer instability located at the vortex periphery. Although the most unstable disturbance has a characteristic vertical scale which is comparable to the vortex height, interestingly, the critical levels of the successively fastest growing modes are closely spaced at intervals along the axial direction that are much smaller than the vortex height.     

论辽河群层序的有序性

从排列顺序、基本地层单位、稳定的岩性变化面或标志层、相变、层控矿床、褶皱构造六个方面分析,表明辽河群层序是有序的。辽河群遭受三次变形,即:下降阶段的下部构造层次的变形,有压扁作用和重结晶作用,形成广域流劈理和区域变质岩;上升阶段的中间构造层次(A)的变形,有重力滑动形成的不协调褶皱、顺层剪切形成的韧性剪切带与层内(片内)褶皱和水平拉张形成的拉伸线理与线状构造;褶皱阶段的中间构造层次(B)的变形,有局部出现劈理的平行褶皱与相似褶皱并存,伴生有逆冲型韧性剪切带和逆冲-推覆构造。这种两次垂直运动变形和一次水平挤压运动变形的构造模式是决定辽河群层序有序性的构造基础。流劈理不是拉伸、轴面片理、多期构造作用的构造置换等成因机制形成的,而是在垂直压扁下化学成因的产物,可称顺层片理或构造层理。流劈理的成因机制是讨论辽河群层序有序性的核心问题。     

Flow frequency responses to hardwood-to-grass conversion and subsequent succession

A 8.9 ha (22 acre) catchment at the Coweeta Hydrologic Laboratory in western North Carolina was cleared of hardwood forest in 1958 and 1959 and seeded to Kentucky 31 fescue grass in 1959 and 1960. Grass production was high in years when fertilizer was applied and water yield was very similar to that expected from the original forest cover. as grass production declined, so water yields rose, with important increases in the magnitude of both low frequency flows and, particularly, in baseflow. in 1967 and 1968, when all vegetation was deadened in the catchment, the discharge levels in all flow frequency classes were higher. Natural revegetation was then allowed and water yields gradually declined towards the expected level, although there remained a tendency for winter flows to remain higher, and for summer flows to be lower than expected. This paper updates the earlier work of Hibbert (1969) and uses flow duration curves to extend his results.     

条件不稳定湿大气中三维理想地形上空对流的动力学特征

条件不稳定湿大气情况下,气流经过三维地形可以形成不同性质的对流系统以及不同特征的地形流结构,其对流系统、地形流的性质主要取决于地形上空的对流触发、对流-地形流-重力波三者之间的相互作用,同样这些过程对于地形降水的性质、分布起重要的作用.根据不同湿Fr数(Froude number),湿条件不稳定大气经过三维小尺度山地上空时其对流和地形流动存在4种不同的流域(flow regirnes):(1)下游传播对流模态;(2)上游传播和下游传播共存对流模态;(3)山峰附近准静止和下游传播共存对流模态;(4)下坡稳定和下游传播对流共存模态.地形上空对流系统主要可以通过两种不同机制形成:(1)地形直接的抬升或减速作用;(2)在地形流形成后,由于地形流本身特性(如上游分离、背风涡旋和下坡重力波破碎)触发.在较大的Fr数情况下,地形上空对流生成后反过来可以破坏上、下游的地形流结构,但对背风坡的重力波破碎影响较小.不同初始对流有效位能(CAPE)不仅可以影响对流系统的传播、发展,而且可以影响整体地形流性质.较低的初始CAPE有利于地形流的形成,此时对流对地形流结构特征的影响相对较小,其流场性质与低Fr数流域性质相似.     

Size fractionation and optical properties of colloids in an organic-rich estuary (Thurso, UK)

The optical characteristics of a black water river estuary from the north coast of Scotland were examined in the filtered (0.4 µm), ultrafiltered (5 kDa) and colloid-enriched fractions of estuarine samples. The samples were collected over the full salinity range during a period when the pH was relatively constant (8.2–8.5) throughout the estuary, allowing the influence of salinity on estuarine colloidal processes to be distinguished. The properties examined in the bulk, the low molecular weight (LMW) and the colloidal fraction (HMW) were UV–visible absorption, 3-D fluorescence excitation–emission matrix (EEM) spectrum, inorganic and organic carbon, mean size (by dynamic light scattering), and size distribution by flow field-flow fractionation analysis (FlFFF). The combined results of these analyses support the view that river-borne, humic-rich colloids underwent two types of transformation upon mixing with the seawater end member. The first one resulted in an apparent increase in the abundance of LMW constituents and may be explained by coiling of the individual humic macromolecules. The second one resulted in an increase in the mean size measured in both the lower and higher colloidal size ranges, and may be explained by aggregation of colloids to form entities that were still mostly colloidal i.e., smaller than 0.4 µm. The LMW contribution to the bulk optical properties increased with increasing salinity. Very similar findings were obtained from simulated mixing experiments using a Nordic Reference NOM extract as a source of freshwater colloids. This indicates that changes in the molecular architecture and molar mass of river-borne colloids—not changes in their chemical nature—were responsible for the observed variations in the spectral characteristics of CDOM in this estuary.     

细网格非静力二维高阶闭合模式对山体流场特征的模拟分析

本文采用二阶矩湍流闭合方案，分别就非静力和准静力两种条件建立ＰＢＬ数值模式，并模拟了二维山脊流场的结构，计算了二维山体对气流平均场和湍流场的影响。计算结果表明，无论是平均场还是湍流场，采用准静力假设都会造成模拟结果的较大偏差，且对平均场的影响比对湍流场的影响更为显著。两种模式计算结果的差别还随地形坡度和背景风增大而增大。     

Effects of water quality on infiltration,runoff and interrill erosion processes during simulated rainfall

This paper discusses the effects of water quality on the hydrological and erosion response of non‐saline, non‐sodic soils during simulated rain experiments. It is well known that rain water quality affects the behaviour of saline soils. In particular, rain simulation experiments cannot be run using tap water if realistic values of infiltration rates and soil erosion are to be found. This paper reports on similar effects for non‐saline, non‐sodic soils. Two soils – a well‐aggregated clay‐rich soil developed on marine silty clay deposits and a soil developed on silt loam – were selected and subjected to a series of simulated rainstorms using demineralized water and tap water. The experiments were conducted in two different laboratories in order to obtain results independent of the tap water quality or the rainfall simulator characteristics. The results indicate that time‐to‐ponding is largely delayed by solute‐rich water (tap water). When tap water is used, infiltration rates are significantly overestimated, i.e. by more than 100 per cent. Interrill erosion rates increase by a factor of 2·5–3 when demineralized water is used. The silty clay soil was more affected by the water quality than the silt loam soil, with respect to infiltration and runoff production. Regarding interrill erosion rates, the two tested soils were similarly affected by the water quality. Therefore, it can be concluded that rainfall simulation experiments with non‐dispersive soils (e.g. non‐saline, non‐sodic) must also be conducted using water with very low electrical conductivity (i.e. less than 30–50 µS cm⁻¹), close to that of distilled water. The use of tap water certainly hampers comparisons and the relative ranking of the hydrological and erosion response of different soils, while parameter values, such as final infiltration rate or time‐to‐ponding, cannot be extrapolated and extended to natural situations. Therefore, the majority of hydrological and erosion models and parameter values measured during rainfall simulations in the past should be used with caution for all types of soils. Copyright © 2001 John Wiley & Sons, Ltd.     

Short-term changes in the magnitude, frequency and temporal distribution of floods in the Eastern Mediterranean region during the last 45 years — Nahal Oren, Mt. Carmel, Israel

Short-term changes in Eastern Mediterranean precipitation affecting flow regime were documented in Nahal Oren, a 35 km² ephemeral stream in Mt. Carmel, a 500 m high mountain ridge located at the NW coast of Israel. The rainy winter of the Mediterranean type climate (Csa) in Mt. Carmel is characterized by average annual rainfall of 550 mm at the coastal plain to 750 mm at the highest elevation while the summer is hot and dry. Stream flow generates after accumulated rainfall of 120–150 mm while “large floods”, defined as flows with peak discharge of > 5 m³ s^− 1 and/or > 150,000 m³ in volume, are generated in response to rainfall of over 100 mm. Hence, large floods in Nahal Oren stream occur not earlier than December. Precipitation and flow data were divided into two sub-periods: 1957–1969 and 1991–2003 and compared to each other. The results indicate a clear increase in the frequency of large floods, their magnitudes and volumes during the second period with no parallel change in the annual precipitation. Similarly, an increase in storm rainfall–runoff ratio from < 5% to > 15% and a decrease in the threshold rainfall for channel flow by 16–25% were documented. These short-term variations in flooding behavior are explained by the clear decrease in the length of the rainy season and by the resulting significant shortening in the duration of the dry-spells. The increase in the number of large rainfall events and the large floods in each hydrological year together with the increasing number of years with no floods indicate strengthening of their uncertainty of behavior.