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1.
A modelling study of residence time in a macro-tidal estuary 总被引：2，自引：0，他引：2
This paper outlines a numerical modelling study to predict the average residence time of a conservative tracer in a macro-tidal estuary, namely the Mersey Estuary, UK. An integrated hydrodynamic-dispersion model was used to predict the average residence time in the estuary for various tidal level and freshwater discharge conditions. The numerical model was verified against six sets of field measured hydrodynamic data, with the model-predicted water elevations and salinity levels generally agreeing well with the field measurements. The numerical model results show that in the Mersey Estuary both the tidal level and river discharge affect significantly the predicted average residence time. The value of the average residence time is also shown to be closely linked to the intensity of the residual tidal current. This is due to the fact that a large proportion of the Upper and Inner Estuary dries out during low tides, thus a significant amount of the tracer material is transported through the deep channels. An increase in the freshwater discharge causes a considerable increase in the intensity of the residual current along the main channels and thus a reduction in the average residence time. The predicted overall tracer residence time for the whole estuary is relatively short for a relatively large estuary, ranging from less than 1 day to 4 days for various tidal level and freshwater flow combinations. When the tidal range and freshwater discharge are both small, then the local tracer residence time in the upper part of the estuary can be significantly longer than the values predicted for the middle and lower reaches of the estuary. 相似文献
2.
W.R. Geyer 《Estuarine, Coastal and Shelf Science》1997,44(6):713-722
Observations of two small estuaries in Cape Cod, U.S.A. indicate large variations in salinity structure that are forced by variations in along-estuary wind stress. During onshore winds, the estuarine circulation is reduced, and the along-estuary salinity gradient increases as freshwater accumulates. During offshore winds, the surface outflow is enhanced, freshwater is flushed out of the estuary, and the along-estuary salinity gradient becomes weak. Constrictions block the wind-induced flushing, resulting in strong salinity fronts across the constrictions. The residence time of one of the estuaries varies by more than a factor of three in response to variations in wind-induced flushing. The other estuary has little variation of flushing associated with winds, due to a constriction at the mouth that inhibits the wind-induced exchange. The strong influence of winds on the flushing of these estuaries is due in part to their shallow depths, which accentuates the influence of wind stress relative to the effects of the horizontal density gradient. In addition, the residence times of the estuaries are comparable to the time scale of wind forcing, allowing large changes in water properties during wind events. 相似文献
3.
The interannual variation of the behavior of Changjiang freshwater has been investigated using the Princeton Ocean Model (POM).
Five experiments are described in this study. Three basic experiments (Exps. B1, B2 and B3) were performed to examine the
freshwater behavior in response to annual variations of the Changjiang discharge in normal, wet and dry years, respectively.
Thereafter, the freshwater variation was investigated with the model forced by primary-interannual variations of river discharge
with an 8-year period (Exp. I1) and a wind field with a 3.6-year period (Exp. I2). In Exp. B1, the average residence time
of freshwater is roughly estimated to be 681.4 days in the Yellow Sea (YS) and 353.4 days in the combined area of the East
China Sea (ECS) and the Chinese Coast (CC). This difference is attributed to the current pattern in each region and freshwater
exchange among the regions. The interannual variation of freshwater volume in Exp. I1 has a large amplitude and long phase
lag in the YS (38 km3 and 1.6-year against primary-interannual discharge variation), while there are relatively small amplitudes and short phase
lags in the ECS (18 km3 and 0.7-year) and the CC (14 km3 and 0.5-year). It is concluded that the difference in the freshwater behavior results from the difference in the average
residence time in each region. 相似文献
4.
Rolando S. Balotro Atsuhiko Isobe Manabu Shimizu Atsushi Kaneda Takatoshi Takeuchi Hidetaka Takeoka 《Journal of Oceanography》2002,58(6):759-773
An attempt was made to reproduce the circulation pattern in Suo-Nada, Japan during spring and summer season in order to elucidate
the water exchange mechanism in the basin. Two hydrographic surveys at the end of each season were conducted covering the
entire Suo-Nada area. A three-dimensional hydrodynamic Princeton Ocean Model (POM) was used to compute the current resulting
from the observed density and wind field. During spring, a very pronounced counter clockwise gyre is situated near the opening
of the basin. This is replaced by a clockwise circulation which seemed to occupy the whole domain during summer. Within each
season, however, the vertical distribution of current does not show any remarkable differences, indicating the dominance of
horizontal current and a very weak estuarine flow. These observational and numerical results were used to estimate the remnant
function and the corresponding average residence time of permanently dissolved matter (PDM) and transformable matter (TM).
The results revealed a small difference in the average residence times of materials within each season but a large seasonal
variability between spring and summer. Furthermore, calculations based on climatological density fields have indicated a similar
trend of variation between the seasonal values of average residence times.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
R. A. Heath 《新西兰海洋与淡水研究杂志》2013,47(3):429-444
Thirty‐two New Zealand coastal inlets are tentatively classified into seven groups with probable similar circulation patterns, based on ratios of their physical parameters: volume, tidal compartment, entrance width, surface area, length, and average width. Eighteen of these have a predominant tidal flow, shown from their small ratio (ß < 4) of tidal compartment to total volume, and the cross‐sectional areas of their entrances are controlled by the tidal flow: Moutere, Waimea, Aotea, Whanganui, Avon‐Heathcote, Tauranga, Parengarenga, Porirua‐Pauatahanui, Kawhia, Nelson, Rangaunu, Raglan, Whangarei, Bluff, Otago, Hokianga, Manukau, and Whangaruru. The other fourteen range from long narrow sounds with probable strong vertical circulation (e.g., Pelorus Sound) to large bays with strong mean horizontal circulations (e.g., Tasman and Hawke Bays). Examples of residence time calculated in inlets with ß > 4 are given for Tasman Bay, a bay with a mean horizontal circulation, which has a residence time of 1–3 months, and Pelorus Sound, an inlet with a vertically complex circulation, which has a residence time of about 20 d. 相似文献
6.
利用Fluent软件模拟雷诺数为200时不同间距比G/D和直径比d/D情况下的圆柱绕流现象。根据模拟结果分析G/D和d/D对圆柱体的涡脱落形态,大、小柱体的升力,阻力系数和St数的影响,结果表明涡脱落形态随着G/D和d/D的变化呈现不同的形式,在G/D小于临界间距比时呈现单一涡脱落形态,在G/D大于临界间距比时,呈现双旋涡脱落形态;临界间距比随着d/D增大而增大。在临界间距比附近大、小柱体的升力和阻力系数值及St数变化较大,大、小柱体的St数具有相同的变化规律,St随着d/D的增大而减小。 相似文献
7.
Tetsuo Yanagi 《Journal of Oceanography》1987,43(4):244-250
The characteristics of seasonal variations of water temperature, salinity and density in the upper, middle and lower layers in Osaka Bay are described. Osaka Bay is considered to be an estuary, because the weak mixed state appears in spring and summer and the moderate mixed state in autumn and winter. Osaka Bay is divided into three areas, the eastern shallow area that has a large amplitude of seasonal variation of water temperature and low average salinity, the southwestern deep area which has small amplitude of seasonal variation of water temperature and high average salinity, and the northwestern deep area, which has small amplitude of seasonal variation of water temperature and low average salinity. 相似文献
8.
The morphological changes of multiple intertidal bars (ridges) on a macrotidal beach were examined under low-energy wave conditions during a spring-to-spring tidal cycle. The morphological response was coupled to the tidal water level variations and related residence times for swash processes and surf (breaking waves and bores) over the cross-shore profile. Spring tides induced a large spatial variation in water lines and small residence times for distinct processes. Neap tides narrowed the intertidal area and increased the time for certain processes to work on the sediment at one location. The observed morphological changes could be coupled to the stagnation of processes at a certain bar crest position. The action of surf (breaking waves and bores) played the major role in the onshore migration of the intertidal bars and the simultaneous erosion of the seaward flank. Swash action, responsible for the generation and migration of intertidal bars in microtidal settings, was not the dominant process in causing the observed morphological changes. Intertidal ridges on macrotidal beaches cannot be considered swash bars as suggested by most previous investigations into these morphological features. 相似文献
9.
POC fluxes from euphotic zone estimated from 234Th deficiency in winter in the northwestern North Pacific Ocean 总被引：2，自引：0，他引：2
1IntroductionThefluxesofcarbon,nutrients,andassoci-atedelementsinvolvedinthebiogeochemicalcyclesoutoftheeuphoticzoneareimportantinthestudyofglobalCO2 change.Someworkershaveproposedthatatthesteadystatethefluxofparticulateorganiccarbonoutoftheeuphoticzoneequalsthenewproduction(EppleyandPe-terson,1979;Eppley,1989).Generallytwometh-odscanbeemployedtoobtainthefluxdata.Oneistousesedimenttrapsintheupperocean(<200m)orfloatingsedimenttraps.Thoughthesedimenttraptechnologyhasshowntobeuse-fulfortimeser… 相似文献
10.
The occurrence of the small meander of the Kuroshio, generated south of Kyushu and propagating eastward, was examined using
sea level data collected during 1961–1995 along the south coast of Japan. Intra-annual variation of the sea level was expanded
by the frequency domain empirical orthogonal function (FDEOF) modes, and it was found that the second and third modes are
useful for monitoring the generation and propagation of the small meander. The third FDEOF for periods of 10–100 days has
a phase reversal between Hosojima and Tosa-shimizu with significant amplitude west of Kushimoto, and the amplitude of its
time coefficient is large during the non-large-meander (NLM) period and has a significant peak when the small meander exists
southeast of Kyushu. The second FDEOF for periods of 20–80 days has a phase reversal between Kushimoto and Uragami, and the
amplitude of its time coefficient is large when the small meander propagates to the south of Shikoku. The third FDEOF mode
allowed us to conclude that the small meander occurred 42 times from July 1961 to May 1995, most of them (38) occurring during
the NLM periods. The second FDEOF mode permits the conclusion that half of the 38 small meanders reached south of Shikoku.
Of these, five small meanders influenced transitions of the Kuroshio path from the nearshore NLM path; one caused the offshore
NLM path and four brought about the large meander. About one-tenth of the total number of small meanders are related to the
formation of the large meander. 相似文献
11.
基于长序列潮位资料,采用调和分析和MK检验方法分析了澳门水域及附近海域历史潮波特性,并建立大范围二维潮流数学模型,以珠澳人工岛及澳门新城A区等大型工程为研究对象,研究人类活动影响下的澳门及附近海域水动力变化特征。研究表明,澳门站的年平均高、低潮位在2005—2008年间发生突变,与岸线变化强度的增大存在直接关系;随着澳门围填海强度逐渐减弱,浅水影响系数逐渐减小,涨落潮历时差逐渐减小;1986—2019年间澳门水域潮位变化幅度较小,十字门水道附近涨落潮历时比由1.16增加至1.19,澳门水域涨落潮不对称现象由上游向外海逐渐减小。围填海工程导致澳门水道潮量减小,涨落急流速普遍减小,澳门新城A区人工岛及珠澳口岸工程附近产生雍水现象,流速亦呈减小趋势;围填海工程使得澳门岸线由曲折变为平缓,使得澳门水域内余流略微减小。 相似文献
12.
KANG Yanyu LIANG Junrong GAO Yahui LIN Rongcheng GAO Hu XING Xiaoli MA Jie LUO Qiaoqi 《海洋学报(英文版)》2007,26(5):107-115
The growth and interspecies competition of two red tide algal species Thalassiosira pseudonana Hasle et Heimdal and Gymnodinium sp.were studied under different concentration ratios of nitrogen to phosphorus,and the algal batch culture experiments were conducted.The physiological and biochemical indexes were measured periodically,including the maximum comparing growth rate,relative growth rate,average double time and chlorophyll a concentration.The results showed that when the concentration ratio of nitrogen to phosphorus was 16:1,the maximum comparing growth rate,relative growth rate and chlorophyll a concentration of Thalassiosira pseudonana all reached the highest,and average double time was the shortest.This implied that the optimal concentration ratio of nitrogen to phosphorus of Thalassiosira pseudonana is 16:1.When the concentration ratio of nitrogen to phosphorus was 6:1,the maximum comparing growth rate,relative growth rate and the chlorophyll a concentration of Gymnodinium sp.reached the highest,and average double time was the shortest,so the optimal concentration ratio of nitrogen to phosphorus of Gymnodinium sp.is 6:1.From the growth curves as indicated both in the cell density and the chlorophyll a concentration,it is suggested that the influence of concentration ratio of nitrogen to phosphorus on the chlorophyll a concentration and the cell density are almost the same.Different concentration ratios of nitrogen to phosphorus had weak influence on community succession and the competition between the two algae.Gymnodinium sp.may use the phosphorus in vivo for growth,so it is important to pay attention to the concealment of phosphorus,in order to avoid the outbreak of red tide.On the basis of the importance of nitrogen and phosphorus and the ratio of their concentration,the possible outbreak mechanism of red tide of the two algae was also discussed. 相似文献
13.
本文通过对中国沿海25个观测站水位资料的分析,初步探讨了中国沿海1980-2012年增减水的变化特征及与海平面变化的关系。结果表明:（1）中国沿海增减水的季节变化特征明显,相邻站由于受到的气象状况相同,其沿海增减水变化的过程相近,但是变化幅度存在较大差异。从空间分布看,沿海增减水的变化幅度呈现中间大南北小的区域特征,自长江口至广东沿海,增减水的年变化幅度最大,年变幅平均为5.0~7.5 cm;南海周边及北部湾沿海,增减水的年变化幅度次之,年变幅平均为4.0~5.5 cm;自渤海至黄海沿海,增减水的年变化幅度较小,年变幅平均为3.3~3.5 cm。（2）从时间变化看,1980-2012年中国沿海年平均增减水长期基本没有趋势性变化,但明显存在2至5年的周期性变化信号,该信号的震荡幅度为0.1 cm。经过高频滤波后,对沿海月平均增减水序列与Niño3.4指数进行相关性分析,相关系数为-0.5,该相关系数通过了显著性检验,说明中国沿海的增减水变化与ENSO事件呈现负相关关系。（3）中国沿海增减水的长期变化及空间分布特征均与海平面变化不同。1980-2012年,中国沿海海平面的上升速率为2.9 mm/a,而增减水长期基本无趋势性变化;另外,其季节变化与海平面的季节变化从时间和区域上均不存在一致性。（4）但是,短期海平面的变化与增减水有关,并且增减水对短期海平面的贡献根据其具体情况而定,增水幅度大且持续时间长的过程对短期海平面有抬升作用,其贡献率最大可达65%;反之,减水幅度大且持续时间长的过程则对短期海平面有降低的作用。 相似文献
14.
Zuo Qihua Yang Zhengji .
Senior Engieer River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1996,(3)
- The variation of the amplitude of waves with varying incident angles when waves propagate through a typical approach channel is discussed by a numerical calculation method, the result of which shows that the influence of the channel on wave propagation is obvious. When the wave propagation direction is in coincidence with the channel axis, the wave amplitude ratio will decrease with the increase of propagation distance. When the incident angle is 15 - 30 , there appears an area of larger wave amplitude ratio on the side slope facing the waves, but at the another side, the wave amplitude ratio is generally small, indicating that the channel has a shielding effect. When waves propagate across the channel perpendicularly, the wave amplitude ratio can be calculated with the shallow water coefficient. 相似文献
15.
象山港水交换特性研究 总被引：4，自引：0，他引：4
在验证良好的三维斜压潮流数学模型的基础上,以溶 解态的保守性物质为示踪剂,建立对流-扩散型的海湾水交换数值模型,计算了象山港水体半交换时间和平均滞留时间,并研究了斜压动力对湾内外水交换的贡献。研究结果表明,象山港水交换速度的区域性变化较大,水体半交换时间和平均滞留时间由象山港口门向湾顶逐渐增加,口门附近半交换时间在5d以内,平均滞留时间为5~10 d;湾顶水交换速度缓慢,水体半交换时间为30~35 d,平均滞留时间为35~40d。斜压动力对狭湾外段水交换影响较弱,对狭湾内段有较大的影响。 相似文献
16.
近十年来渤海湾围填海工程对渤海湾水交换的影响 总被引：2，自引：0，他引：2
近十年来我国海岸带地区快速城市化,对土地的需求持续高涨,导致沿海地区围海造地现象愈演愈烈,海湾纳潮海域面积持续萎缩,对海湾的水交换带来了较大压力。为此,选取我国海岸带快速城市化的典型区域——渤海湾为例,研究近十年来渤海湾海岸带城市化对渤海湾水交换的影响。基于国际流行的MIKE3水动力模型耦合粒子追踪模块,应用2000年和2010年两个典型年份的渤海湾岸线资料,分别计算了2000年和2010年渤海湾环流系统及其驱动下的水质点运移规律和变化特征。研究将渤海湾划分为8个区块,定量化研究和对比了近十年来由于渤海湾持续围填海导致的海湾水存留时间和不同区块水交换能力的变化。结果表明,随着近十年来渤海湾沿岸快速城市化产生的岸线变化,导致湾内环流涡旋增多,决定湾内水交换的流场结构发生了显著变化,导致各区块的水交换能力和平均水存留时间不仅存在较大差异,而且发生了显著的变化。与2000年相比,2010年天津港、黄骅港和曹妃甸港区海域的平均水存留时间明显增加,水交换率下降,对区域水质的改善十分不利。 相似文献
17.
Air-floating towing beha viors of multi-bucket foundation plat form （MBFP） are investigated with the 1/20-scale model tests and hydrodynamic so ftware MOSES. MOSES numerical model was val idated by test results, and M OSES prototype model of MBFP can eliminate scale effect of model. The influences of towing factors of to wing speed, water depth, freeboard, and w ave direction on air-floating tow ing stability of MBFP were analyzed by model tests and validated MOSES prototype mod el. It is sho wn that the re duction of towing sp eed can effectively d ecrease the to wing force and surge acceleration to improve towing stability. Water depth is another f actor in towing s tability. Obvious shallow water effect will appear in shallow water with sma ll water depth-draft ratio and it w ill disappear gradually and air-floating towing becomes more stable with the increase of water depth. Accelerations of surge, s way and heave are small and they have modest changes when freeboard increases from 0.5 to 2 m. For MBFP, the freeboard is not suggested to be larger than 2 m in following wave. Wave direction has large influence on the towing stability, the surge acceleration and towing force are sensitive to the va riation of wave direction, the surge acceleration and towing force in following wave （0°） and counter wave （180°） are much larger than that in transverse sea （90°and 270°）. 相似文献
18.
The impact of human activities on the flushing properties of a semi-enclosed lagoon: Xiaohai, Hainan, China 总被引：1，自引：0，他引：1
In this study, a Lagrangian particle tracking model driven by hydrodynamic fields was used to investigate the changes of flushing properties in Xiaohai Lagoon resulting from natural evolution and influences of human activities. Comparisons of residence times between 1936 and 2001 indicate that the flushing efficiency of the lagoon has deteriorated greatly during the past seven decades. Over this period, the average residence time of the lagoon has increased from 45 to 71 days, an increase of 59%. The Lagrangian residual velocity has decreased from 1936 to 2001 in the large portions of the lagoon, and the spatial distribution pattern of the residual current has changed significantly. The well-developed horizontal circulations in 1936 disappeared. Instead, the horizontal Lagrangian residual velocity showed uniformly seaward motion with reduced velocity in 2001. Human activities have incurred great impacts on the deterioration of flushing efficiency. The reduction of river inflow imposed the most significant impact, causing an increase of average residence time by 33%. The land reclamation in the lagoon came as the second most significant factor, causing an increase of 15%. Closure of the North Opening had posed minor impact. The model results suggest that restoring the river inflow, as well as the dredging of the tidal channel and the inner lagoon, should be the top proprieties for future water quality management. 相似文献
19.
Data collected in three Californian estuaries indicate that hypersaline conditions exist during the dry summers typical of a Mediterranean climate. The generalised seasonal and longitudinal hydrographic structures are described and explained. It is argued that this seasonal hypersalinity is common and that it represents a major class of estuaries. The observed accumulation of salt indicates surprisingly long residence times in small basins which have free exchange with the ocean. This semi-isolation of the inner basin leads to a large build-up or severe depletion of nutrients, pollutants and plankton in these systems. Of concern are the trends to increase pollutant loading in the same systems that are experiencing an increase in residence times owing to freshwater extraction in the watershed. 相似文献
20.
Two different methods of estimating the water exchange through the Baltic coastal region of Laxemar have been used, consisting of particle trajectories and passive tracers. Water is traced from and to a small discharge region near the coast. The discharge material in this region is treated as zero-dimensional particles or tracers with neutral buoyancy. The real discharge material could be a leakage of radio-nuclides through the sea floor from an underground repository of nuclear waste.Water exchange rates between the discharge region and the model domain are estimated using both forward and backward trajectories as well as passive tracers. The Lagrangian trajectories can account for the time evolution of the water exchange while the tracers give one average age per model grid box. Water exchange times such as residence time, age and transient times have been calculated with trajectories but only the average age (AvA) for tracers. The trajectory calculations provide a more detailed time evolution than the tracers.On the other hand the tracers are integrated “on-line” simultaneously in the sea circulation model with the same time step while the Lagrangian trajectories are integrated “off-line” from the stored model velocities with its inherent temporal resolution, presently 1 h. The sub-grid turbulence is parameterised as the Laplacian diffusion for the passive tracers and with an extra stochastic velocity for trajectories. The importance of the parameterised sub-grid turbulence for the trajectories is estimated to give an extra diffusion of the same order as the Laplacian diffusion by comparing the Lagrangian dispersions with and without parameterisation. The results of the different methods are similar but depend on the chosen diffusivity coefficient with a slightly higher correlation between trajectories and tracers when integrated with a lower diffusivity coefficient. 相似文献