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1.
M. J. Winterbourn 《新西兰海洋与淡水研究杂志》2013,47(3):399-416
Fluxes of allochthonous litter were studied in a 93‐m long section of a small stream flowing through mountain beech forest at Cass in the South Island of New Zealand. Litter entered the stream throughout the year with maximum input from October to March. Mean annual input of beech litter was estimated to be 567 g.m‐2 (dry weight). Down‐stream movement of litter correlated strongly with maximum stream discharge during the collection period. The seasonal distribution and accumulation of litter within the stream was examined using 1‐mm‐mesh colonisation trays. Litter was unevenly distributed over the stream bed, but the average amounts taken from riffles, pools, and among large stones were similar. Litter accumulations were greatest in a pool in summer. The most important factor governing the quantity and transport of litter within the stream was stream flow. 相似文献
2.
Stream channels are narrower in pasture than in forest 总被引：1，自引：0，他引：1
Robert J. Davies‐Colley 《新西兰海洋与淡水研究杂志》2013,47(5):599-608
In the Hakarimata Range, west of Hamilton, New Zealand, second‐order streams appear to be wider in native than in pasture catchments, whereas streams in pine plantations (18 years old) appear to be suffering active stream‐bank erosion. A working hypothesis to explain these observations was that pasture vegetation replacing original forest encroaches on the stream channel, causing it to become narrower. To test the hypothesis, channel widths were measured up stream and down stream of “transitions” from native forest to pasture in 20 streams of different size in marginal ranges of the Waikato Basin. Small streams (catchment area <1 km2, width in forest <2 m) were found to be half the width in pasture reaches as in forest. The degree of channel narrowing decreased as stream size increased and was minimal in large streams (catchment area >30 km2, width in forest >10 m). This narrowing of stream channels implies that native forest clearance in New Zealand has reduced stream channel habitat. A concern regarding riparian planting for stream restoration is that sediment stored in pasture stream banks could be mobilised if grasses are extinguished by shading, resulting in turbid streamwater and sedimentation of fines in the channel. 相似文献
3.
《Marine Policy》2014
It is likely that there will be a substantial increase in the number of tidal stream turbines within the UK over the next decade. However, the ecological impacts upon marine top-predators, including seabirds, remain largely unknown. Although tidal stream turbines could have many direct and indirect impacts upon seabird populations, it is the risk of direct collisions between individuals and moving components that currently causes the most concern. Species such as Auks Alcidae sp., Cormorants Phalacrocorax sp. and Divers Gavia sp. almost certainly face higher risks than others. However, it is likely that they are not equally vulnerable. Part of predicting which are most vulnerable involves the estimation of spatial overlap between their foraging distributions and the location of tidal stream turbines. This paper reviews potential methods and approaches that should help to predict whether a population would: (1) exploit areas suitable for tidal stream turbines, (2) dive near tidal stream turbines within these areas, or (3) dive to depths where moving components are found? Answering these questions in a hierarchical manner (from 1 to 3) could help to predict the extent of spatial overlap for vulnerable populations. These approaches require a fundamental understanding of the mechanistic links between physical conditions, prey characteristics and foraging opportunities. Therefore, multi-disciplinary approaches incorporating methods usually associated with oceanographic and fisheries studies are needed to document physical conditions and prey characteristics over large and small spatial scales. Answering these questions also requires collaborative efforts and a strategic governance approach to collating the wide range of distributional, prey and physical datasets currently being collected. 相似文献
4.
Frank Chew 《Marine Geodesy》2013,36(1):103-116
Western boundary currents, such as the Gulf Stream, are often modeled as flows in near cross‐stream geostrophic balance with paths that are straight or nearly straight. The effect of planetary vorticity advection on the downstream sea‐level slope in these rectilinear flows is re‐examined and found negligible. Instead, the re‐examination reveals a much greater effect of the ageostrophic component of the horizontal divergence in determining the downstream slope. Overlooked in previous studies is the geostrophic component of the horizontal divergence because of a hidden assumption of parallel flow. To avoid this pitfall, we employ a natural coordinate system to follow precisely the downstream direction. Further, we differentiate between weak geostrophic flows with small accelerations and flows in cross‐stream geostrophic balance where downstream acceleration might be appreciable. Two Rossby numbers are employed: a small cross‐stream number (≤0.01) to describe the near cross‐stream balance, and a large downstream number (≤0.1) to describe the large downstream accelerations that are found in western boundary flows. Finally, by means of a scale analysis we show that over the whole range of possible Rossby numbers, the advection effect of planetary vorticity on downstream sea level slope is negligible compared to the effect of the ageostrophic component of the horizontal divergence. Some new data on the nearshore gradient of the Reynolds stress are also included. 相似文献
5.
Observations on Chatham Rise currents 总被引：2，自引：2，他引：0
New Zealand stream ecosystems differ from many of their North American counterparts, on which general stream ecosystem models are based, in several ways. In New Zealand, large particle detritivores (shredders) are poorly represented, and the dominant invertebrates are browsers which feed on fine particulate organic matter and stone‐surface organic layers. In contrast with the river continuum concept of Vannote et al. (Canadian Journal of Fisheries and Aquatic Sciences 37: 130–137, 1980), representation of functional feeding groups shows little change downstream and a temporal continuum of synchronous species replacements is not found. Many common benthic invertebrates are ecologically flexible species with poorly synchronised life histories. These differences appear to be associated with the non‐retentive, climatically unpredictable nature of the stream environment. The idea that stream communities are highly structured entities is questioned, as is the generality of the river continuum concept. 相似文献
6.
E. N. Badyukova 《Oceanology》2010,50(6):953-960
On the basis of geologic-geomorphologic studies, an alternative concept regarding the evolution of the Northern Caspian Sea
Region and the adjacent areas in the boundary of the Pleistocene-Holocene is presented. A supposition is made about the existence
of a large lagoon in the North Caspian Region that the Volga River emptied into forming a delta. Later, water from the lagoon
flowed as a “stratum” stream into the Black Sea through the Manych Strait. A conclusion is reached that the Baer mounds were
formed on the bottom of this stream. 相似文献
7.
The mechanisms of interaction between stream life and habitat are often complex and poorly understood. We explored the response of a freshwater crayfish (Paranephrops planifrons) to the functions of large wood with a view towards possible future use of wood in stream restoration in New Zealand. We compared three sub‐reach types within a native forest stream in the central North Island, New Zealand; complex wood‐rich, simple (straight) woodless, and geomorphically complex woodless. Stable logs embedded across the channel created considerable habitat heterogeneity, particularly diversity of substrate, water depths and velocities, that was associated with a significantly higher abundance and biomass of crayfish compared with a straight woodless reach. Although undercut banks in woodless sub‐reaches also supported abundant crayfish, wood increased the proportion of stream area used as habitat, apparently by providing surrogate edge habitat. Wood appeared to increase stream complexity by retaining streambed substrate and providing microhabitat with stable cover. 相似文献
8.
应用边界拟合坐标系统，解决了闽江河口河道曲折汊道多造成的计算方向与河底走向交角过大的难点；针对闽江河口长宽比相差较大的特点，移植了通常用于河道计算的沿纵向求解大尺度矩阵问题转化为沿横向小尺度矩阵求逆的水流方程求解方法，采用全隐差分格式，使闽江口数模网格步长最小控制在50m左右，时步长达3min，潮位、流场与实测拟合良好。 相似文献
9.
Robert J. Davies‐Colley Mark A. Meleason Raeme M.J. Hall J. Christopher Rutherford 《新西兰海洋与淡水研究杂志》2013,47(3):673-688
Action is increasingly being taken in New Zealand and elsewhere to restore ecological function to streams through planting of riparian zones. We used simulation modelling to explore the relative performance of three strategies to restore the riparian zone of a pastoral stream to native forest by: (1) passive regeneration; (2) planting then abandonment of a Pinus radiata plantation; and (3) active restoration by planting selected native trees. We linked the forest model LINKNZ with a shade and temperature model (sWAIORA), and a wood model (OSU_STREAMWOOD) to simulate recovery trajectories for key forest stream attributes in hypothetical streams (1.3–14.0 m channel width) in the central North Island, New Zealand. Both active restoration strategies outperformed passive regeneration in shade, temperature and stream wood volume for most of the simulation time (800 years). Although the abandoned pine plantation provided greatest shade initially (<100 years), active native planting provided the greatest benefits overall. In general, recovery of stream shade (and temperature) is expected within decades, is accelerated by deliberate planting, and is fastest in small streams in which thermal stress from sunlight exposure is greatest. However, full recovery of stream and riparian function may take centuries, being dependent on large trees providing wood to structure the channel. 相似文献
10.
舟山海域特定水道潮流能估算 总被引：2，自引：0，他引：2
对舟山海域高亭水道5个站位、灌门水道8个站位的连续26 h实测潮流资料进行分析。结果表明:高亭水道和灌门水道均为不规则半日潮,各站总的垂向平均流速在1 m/s以上。介绍了国际上常用的估算潮流能的方法:Farm方法和Flux方法,并用这2种方法分别对高亭水道和灌门水道潮流能进行估算。近似得到高亭水道可开发潮流能功率在4.67~5.31 MW之间,灌门水道可开发潮流能功率在7.92~9.37 MW之间。综合2水道可开发潮流能,换算成1 a的发电量,约占舟山市2005年用电总量的6%~7%。 相似文献
11.
Robert J. Wilcock Graham B. McBride John W. Nagels Grant L. Northcott 《新西兰海洋与淡水研究杂志》2013,47(2):277-288
Abstract The Whangamaire Stream (North Island, New Zealand) has high concentrations of nitrate nitrogen (NO? 3‐N), biochemical oxygen demand (BOD5), and Kjeldahl nitrogen (TKN) as a result of catchment land use practices. The lower reaches of the stream drain intensively farmed land and have dissolved oxygen (DO) levels of 10–50% saturation. The dominant riparian vegetation, Apium nodiflorum, provides a large organic loading by intercepting nutrients in run‐off and then decaying in the stream channel. Water quality and reaeration aspects of the stream were studied in order to explain the observed low DO levels. Measurements of the reaeration coefficient at 20°C, K2 20, using methyl chloride (CH3Cl) as a gas tracer, yielded values of 1.1–3.0 d?1 for the upper part of the study reach and 15.5–16.2 d?1 for the lower reach (overall average 12.5 ± 2.5 d?1). These were in agreement with values inferred from single‐station diurnal curve analysis, which also showed that respiration was dominant in the lower reach where photo‐synthetic activity was inhibited by shade. The relatively large reaeration coefficients ensure that parts of the stream do not become anoxic at night time. Better riparian management and reduced nutrient inputs are likely to improve stream water quality. 相似文献
12.
13.
Owen M. Griffin 《Ocean Engineering》1981,8(2):129-209
Vortex-excited oscillations of marine structures result in reduced fatigue life, large hydrodynamic forces and induced stresses, and sometimes lead to structural damage and to destructive failures. The cold water pipe of an Ocean Thermal Energy Conversion (OTEC) plant is nominally a bluff, flexible cylinder with a large aspect ratio (L/D = length/diameter), and is likely to be susceptible to resonant vortex-excited oscillations. The objective of this paper is to survey recent results pertaining to the vortex-excited oscillations of structures in general and to consider the application of these findings to the design of the OTEC cold water pipe. Practical design calculations are given as examples throughout the various sections of the report.This paper is limited in scope to the problems of vortex shedding from bluff, flexible structures in steady currents and the resulting vortex-excited oscillations. The effects of flow non-uniformities, surface roughness of the cylinder, and inclination to the incident flow are considered in addition to the case of a smooth cylinder in a uniform stream. Emphasis is placed upon design procedures, hydrodynamic coefficients applicable in practice, and the specification of structural response parameters relevant to the OTEC cold water pipe. There are important problems associated with the shedding of vortices from cylinders in waves and from the combined action of waves and currents, but these complex fluid/structure interactions are not considered in this paper. 相似文献
14.
The present paper proposes a numerical model to determine horizontal and vertical components of the hydrodynamic forces on a slender submarine pipeline lying at the sea bed and exposed to non-linear waves plus a current. The new model is an extension of the Wake II type model, originally proposed for sinusoidal waves (Soedigdo et al., 1999) and for combined sinusoidal waves and currents (Sabag et al., 2000), to the case of periodic or random waves, even with a superimposed current. The Wake II type model takes into account the wake effects on the kinematic field and the time variation of drag and lift hydrodynamic coefficients. The proposed extension is based on an evolutional analysis carried out for each half period of the free stream horizontal velocity at the pipeline. An analytical expression of the wake velocity is developed starting from the Navier–Stokes and the boundary layer equations. The time variation of the drag and lift hydrodynamic coefficients is obtained using a Gaussian integration of the start-up function. A reduced scale laboratory investigation in a large wave flume has been conducted in order to calibrate the empirical parameters involved in the proposed model. Different wave and current conditions have been considered and measurements of free stream horizontal velocities and dynamic pressures on a bottom-mounted pipeline have been conducted. The comparison between experimental and numerical hydrodynamic forces shows the accuracy of the new model in evaluating the time variation of peaks and phase shifts of the horizontal and vertical wave and current induced forces. 相似文献
15.
AO Hughes 《新西兰海洋与淡水研究杂志》2016,50(2):277-290
Improvements in riparian management, such as shrub/tree planting and livestock exclusion, are often assumed to result in reduced stream bank erosion and associated catchment sediment yield. Studies that quantify the effectiveness of riparian interventions aimed at reducing bank erosion and river sediment yields are, however, rare. This paper discusses how bank erosion processes can vary throughout catchments (with particular reference to their scale dependence) and hence how the effectiveness of different riparian interventions can be variable. The findings of known published accounts of the effectiveness of riparian management interventions for reducing stream bank erosion in New Zealand are also summarised. Only nine relevant studies were identified and most used qualitative or semi-quantitative analysis methods. Most studies compared stream banks in pasture catchments (with unlimited livestock access) with stream banks where livestock were excluded and riparian shrubs/trees were present. Many studies reported that managed stream banks were in better condition than unmanaged banks. The exclusion of livestock from riparian areas was generally reported as the principal factor in the measured improvements or differences. Only two studies specifically attributed reduced stream bank erosion to the presence of riparian vegetation. The dearth of research identified here highlights the need for further quantitative studies to determine the effectiveness of riparian management measures for reducing bank erosion. 相似文献
16.
Large-eddy simulation of turbulent flow past a circular cylinder at sub- to super-critical Reynolds numbers is performed using a high-fidelity orthogonal curvilinear grid solver. Verification studies investigate the effects of grid resolution, aspect ratio and convection scheme. Monotonic convergence is achieved in grid convergence studies. Validation studies use all available experimental benchmark data. Although the grids are relatively large and fine enough for sufficiently resolved turbulence near the cylinder, the grid uncertainties are large indicating the need for even finer grids. Large aspect ratio is required for sub-critical Reynolds number cases, whereas small aspect ratio is sufficient for critical and super-critical Reynolds number cases. All the experimental trends were predicted with reasonable accuracy, in consideration the large facility bias, age of most of the data, and differences between experimental and computational setup in particular free stream turbulence and roughness. The largest errors were for under prediction of turbulence separation. 相似文献
17.
O. A. Bukin Nguen Suan An A. N. Pavlov S. Yu. Stolyarchuk K. A. Shmirko 《Izvestiya Atmospheric and Oceanic Physics》2011,47(5):610-618
The paper describes a lidar and presents the results of lidar sensing of the vertical ozone distribution (VOD); the lidar measurements are analyzed together with data from a network of meteorological stations situated along the 132° E meridian. VODs over Primorye and Japan in the winter period are compared. An analysis showed that an interrelation exists between the subtropical jet stream and the structures of VOD and tropopause inversion layer. Specifically, the region of the VOD local maximum above the tropopause is in the upper part of the tropopause inversion layer and the width of the maximum depends on the distance from the core of the subtropical jet stream. It is found that the local ozone minimum in the lower stratosphere corresponds to the local minimum of the squared Brunt-Vaisala frequency within this same altitude range in the winter season, when two tropopauses frequently overlap. It is conjectured that the local ozone maximum and tropopause inversion layer may be associated with mixing processes in the layer where stratospheric and tropospheric circulation cells come into contact near the core of the subtropical jet stream. 相似文献
18.
潮流发电水轮机基于动量定理的性能计算方法研究 总被引：2，自引：0，他引：2
以潮流发电水轮机的设计为研究背景,分析和总结了基于动量定理方法的四种流管模型(单盘面-单流管模型、双盘面-单流管模型、单盘面-多流管模型和双盘面-多流管模型)在竖轴变攻角水轮机的水动力性能计算中的应用,特别是能量利用率预报方面的应用。说明基于动量定理的模型在求竖轴变攻角潮流发电水轮机的水动力性能方面,能够预报一些定性特性和总体趋势,为水轮机的设计和计算提供一种初步方法。 相似文献
19.
Aurelia labiata medusae (Scyphozoa) in Roscoe Bay avoid tidal dispersion by vertical migration 总被引：2，自引：0，他引：2
Aurelia labiata reside year around in Roscoe Bay on the west coast of Canada in spite of tides that exchange as much as 10% to 30% of the bay's water twice daily. Large numbers of medusae drift eastward over a gravel bar and out of the bay on ebb tides, only to return on flood tides. Drogues released into the tidal stream at the middle of an ebb tide drifted about 700 m out of the bay and into an adjacent large body of water. With the aid of a viewing box and lift net it was observed that after drifting out of the bay on an ebb tide, medusae remained within 300 m of the bay because they swam into still or counter current water below the turbulent ebb stream. When the tide turned to flood, medusae rose into the still water, became embedded in the nonturbulent flood stream, and drifted back into the bay. Vertical migration appears to enable the dense population of medusae to stay in a single location. This enhances reproductive success by keeping males and females in close proximity and increases survival by keeping the population in a favourable location. 相似文献
20.
A. S. Medvedev 《Izvestiya Atmospheric and Oceanic Physics》2007,43(4):436-441
Diabatic-circulation diagnostics with the use of the distributions of heating rates and potential temperature requires that, in each particular case, a special and ambiguously defined correction to the stream function be introduced to turn a globally averaged vertical velocity to zero at any isobaric level. Up to now, the physical nature of this correction has been little explained and it has been usually written in a form that has not been substantiated to a sufficient extent. In this paper, this correction and its uncertainty are related to the eddy term, which is usually neglected in the concept of diabatic velocities. The decomposition of wave fluxes into advective and diffusion components is not unique. As a result, one can formulate a variational problem of minimizing the diffusion component of the wave flux and, thus, the problem of finding advective velocities, which involve the maximum of eddy-induced advection. A unique solution of this problem is obtained, and the relation of the solution to the “standard” diabatic circulation is studied. It is shown that, in the approximation of quasi-horizontal isentropes, the generalized diabatic stream function is identical with the “standard“ stream function. This result partially justifies the correction that is commonly used in calculations of the diabatic circulation. 相似文献